// SPDX-License-Identifier: GPL-2.0-only
/*
* kernel/sched/core.c
*
* Core kernel CPU scheduler code
*
* Copyright (C) 1991-2002 Linus Torvalds
* Copyright (C) 1998-2024 Ingo Molnar, Red Hat
*/
#include <linux/highmem.h>
#include <linux/hrtimer_api.h>
#include <linux/ktime_api.h>
#include <linux/sched/signal.h>
#include <linux/syscalls_api.h>
#include <linux/debug_locks.h>
#include <linux/prefetch.h>
#include <linux/capability.h>
#include <linux/pgtable_api.h>
#include <linux/wait_bit.h>
#include <linux/jiffies.h>
#include <linux/spinlock_api.h>
#include <linux/cpumask_api.h>
#include <linux/lockdep_api.h>
#include <linux/hardirq.h>
#include <linux/softirq.h>
#include <linux/refcount_api.h>
#include <linux/topology.h>
#include <linux/sched/clock.h>
#include <linux/sched/cond_resched.h>
#include <linux/sched/cputime.h>
#include <linux/sched/debug.h>
#include <linux/sched/hotplug.h>
#include <linux/sched/init.h>
#include <linux/sched/isolation.h>
#include <linux/sched/loadavg.h>
#include <linux/sched/mm.h>
#include <linux/sched/nohz.h>
#include <linux/sched/rseq_api.h>
#include <linux/sched/rt.h>
#include <linux/blkdev.h>
#include <linux/context_tracking.h>
#include <linux/cpuset.h>
#include <linux/delayacct.h>
#include <linux/init_task.h>
#include <linux/interrupt.h>
#include <linux/ioprio.h>
#include <linux/kallsyms.h>
#include <linux/kcov.h>
#include <linux/kprobes.h>
#include <linux/llist_api.h>
#include <linux/mmu_context.h>
#include <linux/mmzone.h>
#include <linux/mutex_api.h>
#include <linux/nmi.h>
#include <linux/nospec.h>
#include <linux/perf_event_api.h>
#include <linux/profile.h>
#include <linux/psi.h>
#include <linux/rcuwait_api.h>
#include <linux/rseq.h>
#include <linux/sched/wake_q.h>
#include <linux/scs.h>
#include <linux/slab.h>
#include <linux/syscalls.h>
#include <linux/vtime.h>
#include <linux/wait_api.h>
#include <linux/workqueue_api.h>
#ifdef CONFIG_PREEMPT_DYNAMIC
# ifdef CONFIG_GENERIC_ENTRY
# include <linux/entry-common.h>
# endif
#endif
#include <uapi/linux/sched/types.h>
#include <asm/irq_regs.h>
#include <asm/switch_to.h>
#include <asm/tlb.h>
#define CREATE_TRACE_POINTS
#include <linux/sched/rseq_api.h>
#include <trace/events/sched.h>
#include <trace/events/ipi.h>
#undef CREATE_TRACE_POINTS
#include "sched.h"
#include "stats.h"
#include "autogroup.h"
#include "pelt.h"
#include "smp.h"
#include "stats.h"
#include "../workqueue_internal.h"
#include "../../io_uring/io-wq.h"
#include "../smpboot.h"
EXPORT_TRACEPOINT_SYMBOL_GPL(ipi_send_cpu);
EXPORT_TRACEPOINT_SYMBOL_GPL(ipi_send_cpumask);
/*
* Export tracepoints that act as a bare tracehook (ie: have no trace event
* associated with them) to allow external modules to probe them.
*/
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_hw_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_cpu_capacity_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_compute_energy_tp);
DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
#ifdef CONFIG_SCHED_DEBUG
/*
* Debugging: various feature bits
*
* If SCHED_DEBUG is disabled, each compilation unit has its own copy of
* sysctl_sched_features, defined in sched.h, to allow constants propagation
* at compile time and compiler optimization based on features default.
*/
#define SCHED_FEAT(name, enabled) \
(1UL << __SCHED_FEAT_##name) * enabled |
const_debug unsigned int sysctl_sched_features =
#include "features.h"
0;
#undef SCHED_FEAT
/*
* Print a warning if need_resched is set for the given duration (if
* LATENCY_WARN is enabled).
*
* If sysctl_resched_latency_warn_once is set, only one warning will be shown
* per boot.
*/
__read_mostly int sysctl_resched_latency_warn_ms = 100;
__read_mostly int sysctl_resched_latency_warn_once = 1;
#endif /* CONFIG_SCHED_DEBUG */
/*
* Number of tasks to iterate in a single balance run.
* Limited because this is done with IRQs disabled.
*/
const_debug unsigned int sysctl_sched_nr_migrate = SCHED_NR_MIGRATE_BREAK;
__read_mostly int scheduler_running;
#ifdef CONFIG_SCHED_CORE
DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
/* kernel prio, less is more */
static inline int __task_prio(const struct task_struct *p)
{
if (p->sched_class == &stop_sched_class) /* trumps deadline */
return -2;
if (p->dl_server)
return -1; /* deadline */
if (rt_or_dl_prio(p->prio))
return p->prio; /* [-1, 99] */
if (p->sched_class == &idle_sched_class)
return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
if (task_on_scx(p))
return MAX_RT_PRIO + MAX_NICE + 1; /* 120, squash ext */
return MAX_RT_PRIO + MAX_NICE; /* 119, squash fair */
}
/*
* l(a,b)
* le(a,b) := !l(b,a)
* g(a,b) := l(b,a)
* ge(a,b) := !l(a,b)
*/
/* real prio, less is less */
static inline bool prio_less(const struct task_struct *a,
const struct task_struct *b, bool in_fi)
{
int pa = __task_prio(a), pb = __task_prio(b);
if (-pa < -pb)
return true;
if (-pb < -pa)
return false;
if (pa == -1) { /* dl_prio() doesn't work because of stop_class above */
const struct sched_dl_entity *a_dl, *b_dl;
a_dl = &a->dl;
/*
* Since,'a' and 'b' can be CFS tasks served by DL server,
* __task_prio() can return -1 (for DL) even for those. In that
* case, get to the dl_server's DL entity.
*/
if (a->dl_server)
a_dl = a->dl_server;
b_dl = &b->dl;
if (b->dl_server)
b_dl = b->dl_server;
return !dl_time_before(a_dl->deadline, b_dl->deadline);
}
if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
return cfs_prio_less(a, b, in_fi);
#ifdef CONFIG_SCHED_CLASS_EXT
if (pa == MAX_RT_PRIO + MAX_NICE + 1) /* ext */
return scx_prio_less(a, b, in_fi);
#endif
return false;
}
static inline bool __sched_core_less(const struct task_struct *a,
const struct task_struct *b)
{
if (a->core_cookie < b->core_cookie)
return true;
if (a->core_cookie > b->core_cookie)
return false;
/* flip prio, so high prio is leftmost */
if (prio_less(b, a, !!task_rq(a)->core->core_forceidle_count))
return true;
return false;
}
#define __node_2_sc(node) rb_entry((node), struct task_struct, core_node)
static inline bool rb_sched_core_less(struct rb_node *a, const struct rb_node *b)
{
return __sched_core_less(__node_2_sc(a), __node_2_sc(b));
}
static inline int rb_sched_core_cmp(const void *key, const struct rb_node *node)
{
const struct task_struct *p = __node_2_sc(node);
unsigned long cookie = (unsigned long)key;
if (cookie < p->core_cookie)
return -1;
if (cookie > p->core_cookie)
return 1;
return 0;
}
void sched_core_enqueue(struct rq *rq, struct task_struct *p)
{
if (p->se.sched_delayed)
return;
rq->core->core_task_seq++;
if (!p->core_cookie)
return;
rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
}
void sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags)
{
if (p->se.sched_delayed)
return;
rq->core->core_task_seq++;
if (sched_core_enqueued(p)) {
rb_erase(&p->core_node, &rq->core_tree);
RB_CLEAR_NODE(&p->core_node);
}
/*
* Migrating the last task off the cpu, with the cpu in forced idle
* state. Reschedule to create an accounting edge for forced idle,
* and re-examine whether the core is still in forced idle state.
*/
if (!(flags & DEQUEUE_SAVE) && rq->nr_running == 1 &&
rq->core->core_forceidle_count && rq->curr == rq->idle)
resched_curr(rq);
}
static int sched_task_is_throttled(struct task_struct *p, int cpu)
{
if (p->sched_class->task_is_throttled)
return p->sched_class->task_is_throttled(p, cpu);
return 0;
}
static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie)
{
struct rb_node *node = &p->core_node;
int cpu = task_cpu(p);
do {
node = rb_next(node);
if (!node)
return NULL;
p = __node_2_sc(node);
if (p->core_cookie != cookie)
return NULL;
} while (sched_task_is_throttled(p, cpu));
return p;
}
/*
* Find left-most (aka, highest priority) and unthrottled task matching @cookie.
* If no suitable task is found, NULL will be returned.
*/
static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
{
struct task_struct *p;
struct rb_node *node;
node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
if (!node)
return NULL;
p = __node_2_sc(node);
if (!sched_task_is_throttled(p, rq->cpu))
return p;
return sched_core_next(p, cookie);
}
/*
* Magic required such that:
*
* raw_spin_rq_lock(rq);
* ...
* raw_spin_rq_unlock(rq);
*
* ends up locking and unlocking the _same_ lock, and all CPUs
* always agree on what rq has what lock.
*
* XXX entirely possible to selectively enable cores, don't bother for now.
*/
static DEFINE_MUTEX(sched_core_mutex);
static atomic_t sched_core_count;
static struct cpumask sched_core_mask;
static void sched_core_lock(int cpu, unsigned long *flags)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
int t, i = 0;
local_irq_save(*flags);
for_each_cpu(t, smt_mask)
raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
}
static void sched_core_unlock(int cpu, unsigned long *flags)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
int t;
for_each_cpu(t, smt_mask)
raw_spin_unlock(&cpu_rq(t)->__lock);
local_irq_restore(*flags);
}
static void __sched_core_flip(bool enabled)
{
unsigned long flags;
int cpu, t;
cpus_read_lock();
/*
* Toggle the online cores, one by one.
*/
cpumask_copy(&sched_core_mask, cpu_online_mask);
for_each_cpu(cpu, &sched_core_mask) {
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
sched_core_lock(cpu, &flags);
for_each_cpu(t, smt_mask)
cpu_rq(t)->core_enabled = enabled;
cpu_rq(cpu)->core->core_forceidle_start = 0;
sched_core_unlock(cpu, &flags);
cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask);
}
/*
* Toggle the offline CPUs.
*/
for_each_cpu_andnot(cpu, cpu_possible_mask, cpu_online_mask)
cpu_rq(cpu)->core_enabled = enabled;
cpus_read_unlock();
}
static void sched_core_assert_empty(void)
{
int cpu;
for_each_possible_cpu(cpu)
WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
}
static void __sched_core_enable(void)
{
static_branch_enable(&__sched_core_enabled);
/*
* Ensure all previous instances of raw_spin_rq_*lock() have finished
* and future ones will observe !sched_core_disabled().
*/
synchronize_rcu();
__sched_core_flip(true);
sched_core_assert_empty();
}
static void __sched_core_disable(void)
{
sched_core_assert_empty();
__sched_core_flip(false);
static_branch_disable(&__sched_core_enabled);
}
void sched_core_get(void)
{
if (atomic_inc_not_zero(&sched_core_count))
return;
mutex_lock(&sched_core_mutex);
if (!atomic_read(&sched_core_count))
__sched_core_enable();
smp_mb__before_atomic();
atomic_inc(&sched_core_count);
mutex_unlock(&sched_core_mutex);
}
static void __sched_core_put(struct work_struct *work)
{
if (atomic_dec_and_mutex_lock(&sched_core_count, &sched_core_mutex)) {
__sched_core_disable();
mutex_unlock(&sched_core_mutex);
}
}
void sched_core_put(void)
{
static DECLARE_WORK(_work, __sched_core_put);
/*
* "There can be only one"
*
* Either this is the last one, or we don't actually need to do any
* 'work'. If it is the last *again*, we rely on
* WORK_STRUCT_PENDING_BIT.
*/
if (!atomic_add_unless(&sched_core_count, -1, 1))
schedule_work(&_work);
}
#else /* !CONFIG_SCHED_CORE */
static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
static inline void
sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
#endif /* CONFIG_SCHED_CORE */
/*
* Serialization rules:
*
* Lock order:
*
* p->pi_lock
* rq->lock
* hrtimer_cpu_base->lock (hrtimer_start() for bandwidth controls)
*
* rq1->lock
* rq2->lock where: rq1 < rq2
*
* Regular state:
*
* Normal scheduling state is serialized by rq->lock. __schedule() takes the
* local CPU's rq->lock, it optionally removes the task from the runqueue and
* always looks at the local rq data structures to find the most eligible task
* to run next.
*
* Task enqueue is also under rq->lock, possibly taken from another CPU.
* Wakeups from another LLC domain might use an IPI to transfer the enqueue to
* the local CPU to avoid bouncing the runqueue state around [ see
* ttwu_queue_wakelist() ]
*
* Task wakeup, specifically wakeups that involve migration, are horribly
* complicated to avoid having to take two rq->locks.
*
* Special state:
*
* System-calls and anything external will use task_rq_lock() which acquires
* both p->pi_lock and rq->lock. As a consequence the state they change is
* stable while holding either lock:
*
* - sched_setaffinity()/
* set_cpus_allowed_ptr(): p->cpus_ptr, p->nr_cpus_allowed
* - set_user_nice(): p->se.load, p->*prio
* - __sched_setscheduler(): p->sched_class, p->policy, p->*prio,
* p->se.load, p->rt_priority,
* p->dl.dl_{runtime, deadline, period, flags, bw, density}
* - sched_setnuma(): p->numa_preferred_nid
* - sched_move_task(): p->sched_task_group
* - uclamp_update_active() p->uclamp*
*
* p->state <- TASK_*:
*
* is changed locklessly using set_current_state(), __set_current_state() or
* set_special_state(), see their respective comments, or by
* try_to_wake_up(). This latter uses p->pi_lock to serialize against
* concurrent self.
*
* p->on_rq <- { 0, 1 = TASK_ON_RQ_QUEUED, 2 = TASK_ON_RQ_MIGRATING }:
*
* is set by activate_task() and cleared by deactivate_task(), under
* rq->lock. Non-zero indicates the task is runnable, the special
* ON_RQ_MIGRATING state is used for migration without holding both
* rq->locks. It indicates task_cpu() is not stable, see task_rq_lock().
*
* p->on_cpu <- { 0, 1 }:
*
* is set by prepare_task() and cleared by finish_task() such that it will be
* set before p is scheduled-in and cleared after p is scheduled-out, both
* under rq->lock. Non-zero indicates the task is running on its CPU.
*
* [ The astute reader will observe that it is possible for two tasks on one
* CPU to have ->on_cpu = 1 at the same time. ]
*
* task_cpu(p): is changed by set_task_cpu(), the rules are:
*
* - Don't call set_task_cpu() on a blocked task:
*
* We don't care what CPU we're not running on, this simplifies hotplug,
* the CPU assignment of blocked tasks isn't required to be valid.
*
* - for try_to_wake_up(), called under p->pi_lock:
*
* This allows try_to_wake_up() to only take one rq->lock, see its comment.
*
* - for migration called under rq->lock:
* [ see task_on_rq_migrating() in task_rq_lock() ]
*
* o move_queued_task()
* o detach_task()
*
* - for migration called under double_rq_lock():
*
* o __migrate_swap_task()
* o push_rt_task() / pull_rt_task()
* o push_dl_task() / pull_dl_task()
* o dl_task_offline_migration()
*
*/
void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
{
raw_spinlock_t *lock;
/* Matches synchronize_rcu() in __sched_core_enable() */
preempt_disable();
if (sched_core_disabled()) {
raw_spin_lock_nested(&rq->__lock, subclass);
/* preempt_count *MUST* be > 1 */
preempt_enable_no_resched();
return;
}
for (;;) {
lock = __rq_lockp(rq);
raw_spin_lock_nested(lock, subclass);
if (likely(lock == __rq_lockp(rq))) {
/* preempt_count *MUST* be > 1 */
preempt_enable_no_resched();
return;
}
raw_spin_unlock(lock);
}
}
bool raw_spin_rq_trylock(struct rq *rq)
{
raw_spinlock_t *lock;
bool ret;
/* Matches synchronize_rcu() in __sched_core_enable() */
preempt_disable();
if (sched_core_disabled()) {
ret = raw_spin_trylock(&rq->__lock);
preempt_enable();
return ret;
}
for (;;) {
lock = __rq_lockp(rq);
ret = raw_spin_trylock(lock);
if (!ret || (likely(lock == __rq_lockp(rq)))) {
preempt_enable();
return ret;
}
raw_spin_unlock(lock);
}
}
void raw_spin_rq_unlock(struct rq *rq)
{
raw_spin_unlock(rq_lockp(rq));
}
#ifdef CONFIG_SMP
/*
* double_rq_lock - safely lock two runqueues
*/
void double_rq_lock(struct rq *rq1, struct rq *rq2)
{
lockdep_assert_irqs_disabled();
if (rq_order_less(rq2, rq1))
swap(rq1, rq2);
raw_spin_rq_lock(rq1);
if (__rq_lockp(rq1) != __rq_lockp(rq2))
raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
double_rq_clock_clear_update(rq1, rq2);
}
#endif
/*
* __task_rq_lock - lock the rq @p resides on.
*/
struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
__acquires(rq->lock)
{
struct rq *rq;
lockdep_assert_held(&p->pi_lock);
for (;;) {
rq = task_rq(p);
raw_spin_rq_lock(rq);
if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
rq_pin_lock(rq, rf);
return rq;
}
raw_spin_rq_unlock(rq);
while (unlikely(task_on_rq_migrating(p)))
cpu_relax();
}
}
/*
* task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
*/
struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
__acquires(p->pi_lock)
__acquires(rq->lock)
{
struct rq *rq;
for (;;) {
raw_spin_lock_irqsave(&p->pi_lock, rf->flags);
rq = task_rq(p);
raw_spin_rq_lock(rq);
/*
* move_queued_task() task_rq_lock()
*
* ACQUIRE (rq->lock)
* [S] ->on_rq = MIGRATING [L] rq = task_rq()
* WMB (__set_task_cpu()) ACQUIRE (rq->lock);
* [S] ->cpu = new_cpu [L] task_rq()
* [L] ->on_rq
* RELEASE (rq->lock)
*
* If we observe the old CPU in task_rq_lock(), the acquire of
* the old rq->lock will fully serialize against the stores.
*
* If we observe the new CPU in task_rq_lock(), the address
* dependency headed by '[L] rq = task_rq()' and the acquire
* will pair with the WMB to ensure we then also see migrating.
*/
if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
rq_pin_lock(rq, rf);
return rq;
}
raw_spin_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);
while (unlikely(task_on_rq_migrating(p)))
cpu_relax();
}
}
/*
* RQ-clock updating methods:
*/
static void update_rq_clock_task(struct rq *rq, s64 delta)
{
/*
* In theory, the compile should just see 0 here, and optimize out the call
* to sched_rt_avg_update. But I don't trust it...
*/
s64 __maybe_unused steal = 0, irq_delta = 0;
#ifdef CONFIG_IRQ_TIME_ACCOUNTING
irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;
/*
* Since irq_time is only updated on {soft,}irq_exit, we might run into
* this case when a previous update_rq_clock() happened inside a
* {soft,}IRQ region.
*
* When this happens, we stop ->clock_task and only update the
* prev_irq_time stamp to account for the part that fit, so that a next
* update will consume the rest. This ensures ->clock_task is
* monotonic.
*
* It does however cause some slight miss-attribution of {soft,}IRQ
* time, a more accurate solution would be to update the irq_time using
* the current rq->clock timestamp, except that would require using
* atomic ops.
*/
if (irq_delta > delta)
irq_delta = delta;
rq->prev_irq_time += irq_delta;
delta -= irq_delta;
delayacct_irq(rq->curr, irq_delta);
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
if (static_key_false((¶virt_steal_rq_enabled))) {
steal = paravirt_steal_clock(cpu_of(rq));
steal -= rq->prev_steal_time_rq;
if (unlikely(steal > delta))
steal = delta;
rq->prev_steal_time_rq += steal;
delta -= steal;
}
#endif
rq->clock_task += delta;
#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
update_irq_load_avg(rq, irq_delta + steal);
#endif
update_rq_clock_pelt(rq, delta);
}
void update_rq_clock(struct rq *rq)
{
s64 delta;
lockdep_assert_rq_held(rq);
if (rq->clock_update_flags & RQCF_ACT_SKIP)
return;
#ifdef CONFIG_SCHED_DEBUG
if (sched_feat(WARN_DOUBLE_CLOCK))
SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
rq->clock_update_flags |= RQCF_UPDATED;
#endif
delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
if (delta < 0)
return;
rq->clock += delta;
update_rq_clock_task(rq, delta);
}
#ifdef CONFIG_SCHED_HRTICK
/*
* Use HR-timers to deliver accurate preemption points.
*/
static void hrtick_clear(struct rq *rq)
{
if (hrtimer_active(&rq->hrtick_timer))
hrtimer_cancel(&rq->hrtick_timer);
}
/*
* High-resolution timer tick.
* Runs from hardirq context with interrupts disabled.
*/
static enum hrtimer_restart hrtick(struct hrtimer *timer)
{
struct rq *rq = container_of(timer, struct rq, hrtick_timer);
struct rq_flags rf;
WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
rq_lock(rq, &rf);
update_rq_clock(rq);
rq->curr->sched_class->task_tick(rq, rq->curr, 1);
rq_unlock(rq, &rf);
return HRTIMER_NORESTART;
}
#ifdef CONFIG_SMP
static void __hrtick_restart(struct rq *rq)
{
struct hrtimer *timer = &rq->hrtick_timer;
ktime_t time = rq->hrtick_time;
hrtimer_start(timer, time, HRTIMER_MODE_ABS_PINNED_HARD);
}
/*
* called from hardirq (IPI) context
*/
static void __hrtick_start(void *arg)
{
struct rq *rq = arg;
struct rq_flags rf;
rq_lock(rq, &rf);
__hrtick_restart(rq);
rq_unlock(rq, &rf);
}
/*
* Called to set the hrtick timer state.
*
* called with rq->lock held and IRQs disabled
*/
void hrtick_start(struct rq *rq, u64 delay)
{
struct hrtimer *timer = &rq->hrtick_timer;
s64 delta;
/*
* Don't schedule slices shorter than 10000ns, that just
* doesn't make sense and can cause timer DoS.
*/
delta = max_t(s64, delay, 10000LL);
rq->hrtick_time = ktime_add_ns(timer->base->get_time(), delta);
if (rq == this_rq())
__hrtick_restart(rq);
else
smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
}
#else
/*
* Called to set the hrtick timer state.
*
* called with rq->lock held and IRQs disabled
*/
void hrtick_start(struct rq *rq, u64 delay)
{
/*
* Don't schedule slices shorter than 10000ns, that just
* doesn't make sense. Rely on vruntime for fairness.
*/
delay = max_t(u64, delay, 10000LL);
hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
HRTIMER_MODE_REL_PINNED_HARD);
}
#endif /* CONFIG_SMP */
static void hrtick_rq_init(struct rq *rq)
{
#ifdef CONFIG_SMP
INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
#endif
hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
rq->hrtick_timer.function = hrtick;
}
#else /* CONFIG_SCHED_HRTICK */
static inline void hrtick_clear(struct rq *rq)
{
}
static inline void hrtick_rq_init(struct rq *rq)
{
}
#endif /* CONFIG_SCHED_HRTICK */
/*
* try_cmpxchg based fetch_or() macro so it works for different integer types:
*/
#define fetch_or(ptr, mask) \
({ \
typeof(ptr) _ptr = (ptr); \
typeof(mask) _mask = (mask); \
typeof(*_ptr) _val = *_ptr; \
\
do { \
} while (!try_cmpxchg(_ptr, &_val, _val | _mask)); \
_val; \
})
#if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
/*
* Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
* this avoids any races wrt polling state changes and thereby avoids
* spurious IPIs.
*/
static inline bool set_nr_and_not_polling(struct task_struct *p)
{
struct thread_info *ti = task_thread_info(p);
return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
}
/*
* Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
*
* If this returns true, then the idle task promises to call
* sched_ttwu_pending() and reschedule soon.
*/
static bool set_nr_if_polling(struct task_struct *p)
{
struct thread_info *ti = task_thread_info(p);
typeof(ti->flags) val = READ_ONCE(ti->flags);
do {
if (!(val & _TIF_POLLING_NRFLAG))
return false;
if (val & _TIF_NEED_RESCHED)
return true;
} while (!try_cmpxchg(&ti->flags, &val, val | _TIF_NEED_RESCHED));
return true;
}
#else
static inline bool set_nr_and_not_polling(struct task_struct *p)
{
set_tsk_need_resched(p);
return true;
}
#ifdef CONFIG_SMP
static inline bool set_nr_if_polling(struct task_struct *p)
{
return false;
}
#endif
#endif
static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
struct wake_q_node *node = &task->wake_q;
/*
* Atomically grab the task, if ->wake_q is !nil already it means
* it's already queued (either by us or someone else) and will get the
* wakeup due to that.
*
* In order to ensure that a pending wakeup will observe our pending
* state, even in the failed case, an explicit smp_mb() must be used.
*/
smp_mb__before_atomic();
if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
return false;
/*
* The head is context local, there can be no concurrency.
*/
*head->lastp = node;
head->lastp = &node->next;
return true;
}
/**
* wake_q_add() - queue a wakeup for 'later' waking.
* @head: the wake_q_head to add @task to
* @task: the task to queue for 'later' wakeup
*
* Queue a task for later wakeup, most likely by the wake_up_q() call in the
* same context, _HOWEVER_ this is not guaranteed, the wakeup can come
* instantly.
*
* This function must be used as-if it were wake_up_process(); IOW the task
* must be ready to be woken at this location.
*/
void wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
if (__wake_q_add(head, task))
get_task_struct(task);
}
/**
* wake_q_add_safe() - safely queue a wakeup for 'later' waking.
* @head: the wake_q_head to add @task to
* @task: the task to queue for 'later' wakeup
*
* Queue a task for later wakeup, most likely by the wake_up_q() call in the
* same context, _HOWEVER_ this is not guaranteed, the wakeup can come
* instantly.
*
* This function must be used as-if it were wake_up_process(); IOW the task
* must be ready to be woken at this location.
*
* This function is essentially a task-safe equivalent to wake_q_add(). Callers
* that already hold reference to @task can call the 'safe' version and trust
* wake_q to do the right thing depending whether or not the @task is already
* queued for wakeup.
*/
void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
{
if (!__wake_q_add(head, task))
put_task_struct(task);
}
void wake_up_q(struct wake_q_head *head)
{
struct wake_q_node *node = head->first;
while (node != WAKE_Q_TAIL) {
struct task_struct *task;
task = container_of(node, struct task_struct, wake_q);
/* Task can safely be re-inserted now: */
node = node->next;
task->wake_q.next = NULL;
/*
* wake_up_process() executes a full barrier, which pairs with
* the queueing in wake_q_add() so as not to miss wakeups.
*/
wake_up_process(task);
put_task_struct(task);
}
}
/*
* resched_curr - mark rq's current task 'to be rescheduled now'.
*
* On UP this means the setting of the need_resched flag, on SMP it
* might also involve a cross-CPU call to trigger the scheduler on
* the target CPU.
*/
void resched_curr(struct rq *rq)
{
struct task_struct *curr = rq->curr;
int cpu;
lockdep_assert_rq_held(rq);
if (test_tsk_need_resched(curr))
return;
cpu = cpu_of(rq);
if (cpu == smp_processor_id()) {
set_tsk_need_resched(curr);
set_preempt_need_resched();
return;
}
if (set_nr_and_not_polling(curr))
smp_send_reschedule(cpu);
else
trace_sched_wake_idle_without_ipi(cpu);
}
void resched_cpu(int cpu)
{
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
raw_spin_rq_lock_irqsave(rq, flags);
if (cpu_online(cpu) || cpu == smp_processor_id())
resched_curr(rq);
raw_spin_rq_unlock_irqrestore(rq, flags);
}
#ifdef CONFIG_SMP
#ifdef CONFIG_NO_HZ_COMMON
/*
* In the semi idle case, use the nearest busy CPU for migrating timers
* from an idle CPU. This is good for power-savings.
*
* We don't do similar optimization for completely idle system, as
* selecting an idle CPU will add more delays to the timers than intended
* (as that CPU's timer base may not be up to date wrt jiffies etc).
*/
int get_nohz_timer_target(void)
{
int i, cpu = smp_processor_id(), default_cpu = -1;
struct sched_domain *sd;
const struct cpumask *hk_mask;
if (housekeeping_cpu(cpu, HK_TYPE_TIMER)) {
if (!idle_cpu(cpu))
return cpu;
default_cpu = cpu;
}
hk_mask = housekeeping_cpumask(HK_TYPE_TIMER);
guard(rcu)();
for_each_domain(cpu, sd) {
for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
if (cpu == i)
continue;
if (!idle_cpu(i))
return i;
}
}
if (default_cpu == -1)
default_cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
return default_cpu;
}
/*
* When add_timer_on() enqueues a timer into the timer wheel of an
* idle CPU then this timer might expire before the next timer event
* which is scheduled to wake up that CPU. In case of a completely
* idle system the next event might even be infinite time into the
* future. wake_up_idle_cpu() ensures that the CPU is woken up and
* leaves the inner idle loop so the newly added timer is taken into
* account when the CPU goes back to idle and evaluates the timer
* wheel for the next timer event.
*/
static void wake_up_idle_cpu(int cpu)
{
struct rq *rq = cpu_rq(cpu);
if (cpu == smp_processor_id())
return;
/*
* Set TIF_NEED_RESCHED and send an IPI if in the non-polling
* part of the idle loop. This forces an exit from the idle loop
* and a round trip to schedule(). Now this could be optimized
* because a simple new idle loop iteration is enough to
* re-evaluate the next tick. Provided some re-ordering of tick
* nohz functions that would need to follow TIF_NR_POLLING
* clearing:
*
* - On most architectures, a simple fetch_or on ti::flags with a
* "0" value would be enough to know if an IPI needs to be sent.
*
* - x86 needs to perform a last need_resched() check between
* monitor and mwait which doesn't take timers into account.
* There a dedicated TIF_TIMER flag would be required to
* fetch_or here and be checked along with TIF_NEED_RESCHED
* before mwait().
*
* However, remote timer enqueue is not such a frequent event
* and testing of the above solutions didn't appear to report
* much benefits.
*/
if (set_nr_and_not_polling(rq->idle))
smp_send_reschedule(cpu);
else
trace_sched_wake_idle_without_ipi(cpu);
}
static bool wake_up_full_nohz_cpu(int cpu)
{
/*
* We just need the target to call irq_exit() and re-evaluate
* the next tick. The nohz full kick at least implies that.
* If needed we can still optimize that later with an
* empty IRQ.
*/
if (cpu_is_offline(cpu))
return true; /* Don't try to wake offline CPUs. */
if (tick_nohz_full_cpu(cpu)) {
if (cpu != smp_processor_id() ||
tick_nohz_tick_stopped())
tick_nohz_full_kick_cpu(cpu);
return true;
}
return false;
}
/*
* Wake up the specified CPU. If the CPU is going offline, it is the
* caller's responsibility to deal with the lost wakeup, for example,
* by hooking into the CPU_DEAD notifier like timers and hrtimers do.
*/
void wake_up_nohz_cpu(int cpu)
{
if (!wake_up_full_nohz_cpu(cpu))
wake_up_idle_cpu(cpu);
}
static void nohz_csd_func(void *info)
{
struct rq *rq = info;
int cpu = cpu_of(rq);
unsigned int flags;
/*
* Release the rq::nohz_csd.
*/
flags = atomic_fetch_andnot(NOHZ_KICK_MASK | NOHZ_NEWILB_KICK, nohz_flags(cpu));
WARN_ON(!(flags & NOHZ_KICK_MASK));
rq->idle_balance = idle_cpu(cpu);
if (rq->idle_balance && !need_resched()) {
rq->nohz_idle_balance = flags;
raise_softirq_irqoff(SCHED_SOFTIRQ);
}
}
#endif /* CONFIG_NO_HZ_COMMON */
#ifdef CONFIG_NO_HZ_FULL
static inline bool __need_bw_check(struct rq *rq, struct task_struct *p)
{
if (rq->nr_running != 1)
return false;
if (p->sched_class != &fair_sched_class)
return false;
if (!task_on_rq_queued(p))
return false;
return true;
}
bool sched_can_stop_tick(struct rq *rq)
{
int fifo_nr_running;
/* Deadline tasks, even if single, need the tick */
if (rq->dl.dl_nr_running)
return false;
/*
* If there are more than one RR tasks, we need the tick to affect the
* actual RR behaviour.
*/
if (rq->rt.rr_nr_running) {
if (rq->rt.rr_nr_running == 1)
return true;
else
return false;
}
/*
* If there's no RR tasks, but FIFO tasks, we can skip the tick, no
* forced preemption between FIFO tasks.
*/
fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
if (fifo_nr_running)
return true;
/*
* If there are no DL,RR/FIFO tasks, there must only be CFS or SCX tasks
* left. For CFS, if there's more than one we need the tick for
* involuntary preemption. For SCX, ask.
*/
if (scx_enabled() && !scx_can_stop_tick(rq))
return false;
if (rq->cfs.nr_running > 1)
return false;
/*
* If there is one task and it has CFS runtime bandwidth constraints
* and it's on the cpu now we don't want to stop the tick.
* This check prevents clearing the bit if a newly enqueued task here is
* dequeued by migrating while the constrained task continues to run.
* E.g. going from 2->1 without going through pick_next_task().
*/
if (__need_bw_check(rq, rq->curr)) {
if (cfs_task_bw_constrained(rq->curr))
return false;
}
return true;
}
#endif /* CONFIG_NO_HZ_FULL */
#endif /* CONFIG_SMP */
#if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
(defined(CONFIG_SMP) || defined(CONFIG_CFS_BANDWIDTH)))
/*
* Iterate task_group tree rooted at *from, calling @down when first entering a
* node and @up when leaving it for the final time.
*
* Caller must hold rcu_lock or sufficient equivalent.
*/
int walk_tg_tree_from(struct task_group *from,
tg_visitor down, tg_visitor up, void *data)
{
struct task_group *parent, *child;
int ret;
parent = from;
down:
ret = (*down)(parent, data);
if (ret)
goto out;
list_for_each_entry_rcu(child, &parent->children, siblings) {
parent = child;
goto down;
up:
continue;
}
ret = (*up)(parent, data);
if (ret || parent == from)
goto out;
child = parent;
parent = parent->parent;
if (parent)
goto up;
out:
return ret;
}
int tg_nop(struct task_group *tg, void *data)
{
return 0;
}
#endif
void set_load_weight(struct task_struct *p, bool update_load)
{
int prio = p->static_prio - MAX_RT_PRIO;
struct load_weight lw;
if (task_has_idle_policy(p)) {
lw.weight = scale_load(WEIGHT_IDLEPRIO);
lw.inv_weight = WMULT_IDLEPRIO;
} else {
lw.weight = scale_load(sched_prio_to_weight[prio]);
lw.inv_weight = sched_prio_to_wmult[prio];
}
/*
* SCHED_OTHER tasks have to update their load when changing their
* weight
*/
if (update_load && p->sched_class->reweight_task)
p->sched_class->reweight_task(task_rq(p), p, &lw);
else
p->se.load = lw;
}
#ifdef CONFIG_UCLAMP_TASK
/*
* Serializes updates of utilization clamp values
*
* The (slow-path) user-space triggers utilization clamp value updates which
* can require updates on (fast-path) scheduler's data structures used to
* support enqueue/dequeue operations.
* While the per-CPU rq lock protects fast-path update operations, user-space
* requests are serialized using a mutex to reduce the risk of conflicting
* updates or API abuses.
*/
static DEFINE_MUTEX(uclamp_mutex);
/* Max allowed minimum utilization */
static unsigned int __maybe_unused sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
/* Max allowed maximum utilization */
static unsigned int __maybe_unused sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
/*
* By default RT tasks run at the maximum performance point/capacity of the
* system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
* SCHED_CAPACITY_SCALE.
*
* This knob allows admins to change the default behavior when uclamp is being
* used. In battery powered devices, particularly, running at the maximum
* capacity and frequency will increase energy consumption and shorten the
* battery life.
*
* This knob only affects RT tasks that their uclamp_se->user_defined == false.
*
* This knob will not override the system default sched_util_clamp_min defined
* above.
*/
unsigned int sysctl_sched_uclamp_util_min_rt_default = SCHED_CAPACITY_SCALE;
/* All clamps are required to be less or equal than these values */
static struct uclamp_se uclamp_default[UCLAMP_CNT];
/*
* This static key is used to reduce the uclamp overhead in the fast path. It
* primarily disables the call to uclamp_rq_{inc, dec}() in
* enqueue/dequeue_task().
*
* This allows users to continue to enable uclamp in their kernel config with
* minimum uclamp overhead in the fast path.
*
* As soon as userspace modifies any of the uclamp knobs, the static key is
* enabled, since we have an actual users that make use of uclamp
* functionality.
*
* The knobs that would enable this static key are:
*
* * A task modifying its uclamp value with sched_setattr().
* * An admin modifying the sysctl_sched_uclamp_{min, max} via procfs.
* * An admin modifying the cgroup cpu.uclamp.{min, max}
*/
DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
static inline unsigned int
uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
unsigned int clamp_value)
{
/*
* Avoid blocked utilization pushing up the frequency when we go
* idle (which drops the max-clamp) by retaining the last known
* max-clamp.
*/
if (clamp_id == UCLAMP_MAX) {
rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
return clamp_value;
}
return uclamp_none(UCLAMP_MIN);
}
static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
unsigned int clamp_value)
{
/* Reset max-clamp retention only on idle exit */
if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
return;
uclamp_rq_set(rq, clamp_id, clamp_value);
}
static inline
unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
unsigned int clamp_value)
{
struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
int bucket_id = UCLAMP_BUCKETS - 1;
/*
* Since both min and max clamps are max aggregated, find the
* top most bucket with tasks in.
*/
for ( ; bucket_id >= 0; bucket_id--) {
if (!bucket[bucket_id].tasks)
continue;
return bucket[bucket_id].value;
}
/* No tasks -- default clamp values */
return uclamp_idle_value(rq, clamp_id, clamp_value);
}
static void __uclamp_update_util_min_rt_default(struct task_struct *p)
{
unsigned int default_util_min;
struct uclamp_se *uc_se;
lockdep_assert_held(&p->pi_lock);
uc_se = &p->uclamp_req[UCLAMP_MIN];
/* Only sync if user didn't override the default */
if (uc_se->user_defined)
return;
default_util_min = sysctl_sched_uclamp_util_min_rt_default;
uclamp_se_set(uc_se, default_util_min, false);
}
static void uclamp_update_util_min_rt_default(struct task_struct *p)
{
if (!rt_task(p))
return;
/* Protect updates to p->uclamp_* */
guard(task_rq_lock)(p);
__uclamp_update_util_min_rt_default(p);
}
static inline struct uclamp_se
uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
{
/* Copy by value as we could modify it */
struct uclamp_se uc_req = p->uclamp_req[clamp_id];
#ifdef CONFIG_UCLAMP_TASK_GROUP
unsigned int tg_min, tg_max, value;
/*
* Tasks in autogroups or root task group will be
* restricted by system defaults.
*/
if (task_group_is_autogroup(task_group(p)))
return uc_req;
if (task_group(p) == &root_task_group)
return uc_req;
tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
value = uc_req.value;
value = clamp(value, tg_min, tg_max);
uclamp_se_set(&uc_req, value, false);
#endif
return uc_req;
}
/*
* The effective clamp bucket index of a task depends on, by increasing
* priority:
* - the task specific clamp value, when explicitly requested from userspace
* - the task group effective clamp value, for tasks not either in the root
* group or in an autogroup
* - the system default clamp value, defined by the sysadmin
*/
static inline struct uclamp_se
uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
{
struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
struct uclamp_se uc_max = uclamp_default[clamp_id];
/* System default restrictions always apply */
if (unlikely(uc_req.value > uc_max.value))
return uc_max;
return uc_req;
}
unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
{
struct uclamp_se uc_eff;
/* Task currently refcounted: use back-annotated (effective) value */
if (p->uclamp[clamp_id].active)
return (unsigned long)p->uclamp[clamp_id].value;
uc_eff = uclamp_eff_get(p, clamp_id);
return (unsigned long)uc_eff.value;
}
/*
* When a task is enqueued on a rq, the clamp bucket currently defined by the
* task's uclamp::bucket_id is refcounted on that rq. This also immediately
* updates the rq's clamp value if required.
*
* Tasks can have a task-specific value requested from user-space, track
* within each bucket the maximum value for tasks refcounted in it.
* This "local max aggregation" allows to track the exact "requested" value
* for each bucket when all its RUNNABLE tasks require the same clamp.
*/
static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
enum uclamp_id clamp_id)
{
struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
struct uclamp_se *uc_se = &p->uclamp[clamp_id];
struct uclamp_bucket *bucket;
lockdep_assert_rq_held(rq);
/* Update task effective clamp */
p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);
bucket = &uc_rq->bucket[uc_se->bucket_id];
bucket->tasks++;
uc_se->active = true;
uclamp_idle_reset(rq, clamp_id, uc_se->value);
/*
* Local max aggregation: rq buckets always track the max
* "requested" clamp value of its RUNNABLE tasks.
*/
if (bucket->tasks == 1 || uc_se->value > bucket->value)
bucket->value = uc_se->value;
if (uc_se->value > uclamp_rq_get(rq, clamp_id))
uclamp_rq_set(rq, clamp_id, uc_se->value);
}
/*
* When a task is dequeued from a rq, the clamp bucket refcounted by the task
* is released. If this is the last task reference counting the rq's max
* active clamp value, then the rq's clamp value is updated.
*
* Both refcounted tasks and rq's cached clamp values are expected to be
* always valid. If it's detected they are not, as defensive programming,
* enforce the expected state and warn.
*/
static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
enum uclamp_id clamp_id)
{
struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
struct uclamp_se *uc_se = &p->uclamp[clamp_id];
struct uclamp_bucket *bucket;
unsigned int bkt_clamp;
unsigned int rq_clamp;
lockdep_assert_rq_held(rq);
/*
* If sched_uclamp_used was enabled after task @p was enqueued,
* we could end up with unbalanced call to uclamp_rq_dec_id().
*
* In this case the uc_se->active flag should be false since no uclamp
* accounting was performed at enqueue time and we can just return
* here.
*
* Need to be careful of the following enqueue/dequeue ordering
* problem too
*
* enqueue(taskA)
* // sched_uclamp_used gets enabled
* enqueue(taskB)
* dequeue(taskA)
* // Must not decrement bucket->tasks here
* dequeue(taskB)
*
* where we could end up with stale data in uc_se and
* bucket[uc_se->bucket_id].
*
* The following check here eliminates the possibility of such race.
*/
if (unlikely(!uc_se->active))
return;
bucket = &uc_rq->bucket[uc_se->bucket_id];
SCHED_WARN_ON(!bucket->tasks);
if (likely(bucket->tasks))
bucket->tasks--;
uc_se->active = false;
/*
* Keep "local max aggregation" simple and accept to (possibly)
* overboost some RUNNABLE tasks in the same bucket.
* The rq clamp bucket value is reset to its base value whenever
* there are no more RUNNABLE tasks refcounting it.
*/
if (likely(bucket->tasks))
return;
rq_clamp = uclamp_rq_get(rq, clamp_id);
/*
* Defensive programming: this should never happen. If it happens,
* e.g. due to future modification, warn and fix up the expected value.
*/
SCHED_WARN_ON(bucket->value > rq_clamp);
if (bucket->value >= rq_clamp) {
bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
uclamp_rq_set(rq, clamp_id, bkt_clamp);
}
}
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
{
enum uclamp_id clamp_id;
/*
* Avoid any overhead until uclamp is actually used by the userspace.
*
* The condition is constructed such that a NOP is generated when
* sched_uclamp_used is disabled.
*/
if (!static_branch_unlikely(&sched_uclamp_used))
return;
if (unlikely(!p->sched_class->uclamp_enabled))
return;
if (p->se.sched_delayed)
return;
for_each_clamp_id(clamp_id)
uclamp_rq_inc_id(rq, p, clamp_id);
/* Reset clamp idle holding when there is one RUNNABLE task */
if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}
static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
{
enum uclamp_id clamp_id;
/*
* Avoid any overhead until uclamp is actually used by the userspace.
*
* The condition is constructed such that a NOP is generated when
* sched_uclamp_used is disabled.
*/
if (!static_branch_unlikely(&sched_uclamp_used))
return;
if (unlikely(!p->sched_class->uclamp_enabled))
return;
if (p->se.sched_delayed)
return;
for_each_clamp_id(clamp_id)
uclamp_rq_dec_id(rq, p, clamp_id);
}
static inline void uclamp_rq_reinc_id(struct rq *rq, struct task_struct *p,
enum uclamp_id clamp_id)
{
if (!p->uclamp[clamp_id].active)
return;
uclamp_rq_dec_id(rq, p, clamp_id);
uclamp_rq_inc_id(rq, p, clamp_id);
/*
* Make sure to clear the idle flag if we've transiently reached 0
* active tasks on rq.
*/
if (clamp_id == UCLAMP_MAX && (rq->uclamp_flags & UCLAMP_FLAG_IDLE))
rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}
static inline void
uclamp_update_active(struct task_struct *p)
{
enum uclamp_id clamp_id;
struct rq_flags rf;
struct rq *rq;
/*
* Lock the task and the rq where the task is (or was) queued.
*
* We might lock the (previous) rq of a !RUNNABLE task, but that's the
* price to pay to safely serialize util_{min,max} updates with
* enqueues, dequeues and migration operations.
* This is the same locking schema used by __set_cpus_allowed_ptr().
*/
rq = task_rq_lock(p, &rf);
/*
* Setting the clamp bucket is serialized by task_rq_lock().
* If the task is not yet RUNNABLE and its task_struct is not
* affecting a valid clamp bucket, the next time it's enqueued,
* it will already see the updated clamp bucket value.
*/
for_each_clamp_id(clamp_id)
uclamp_rq_reinc_id(rq, p, clamp_id);
task_rq_unlock(rq, p, &rf);
}
#ifdef CONFIG_UCLAMP_TASK_GROUP
static inline void
uclamp_update_active_tasks(struct cgroup_subsys_state *css)
{
struct css_task_iter it;
struct task_struct *p;
css_task_iter_start(css, 0, &it);
while ((p = css_task_iter_next(&it)))
uclamp_update_active(p);
css_task_iter_end(&it);
}
static void cpu_util_update_eff(struct cgroup_subsys_state *css);
#endif
#ifdef CONFIG_SYSCTL
#ifdef CONFIG_UCLAMP_TASK_GROUP
static void uclamp_update_root_tg(void)
{
struct task_group *tg = &root_task_group;
uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
sysctl_sched_uclamp_util_min, false);
uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
sysctl_sched_uclamp_util_max, false);
guard(rcu)();
cpu_util_update_eff(&root_task_group.css);
}
#else
static void uclamp_update_root_tg(void) { }
#endif
static void uclamp_sync_util_min_rt_default(void)
{
struct task_struct *g, *p;
/*
* copy_process() sysctl_uclamp
* uclamp_min_rt = X;
* write_lock(&tasklist_lock) read_lock(&tasklist_lock)
* // link thread smp_mb__after_spinlock()
* write_unlock(&tasklist_lock) read_unlock(&tasklist_lock);
* sched_post_fork() for_each_process_thread()
* __uclamp_sync_rt() __uclamp_sync_rt()
*
* Ensures that either sched_post_fork() will observe the new
* uclamp_min_rt or for_each_process_thread() will observe the new
* task.
*/
read_lock(&tasklist_lock);
smp_mb__after_spinlock();
read_unlock(&tasklist_lock);
guard(rcu)();
for_each_process_thread(g, p)
uclamp_update_util_min_rt_default(p);
}
static int sysctl_sched_uclamp_handler(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
bool update_root_tg = false;
int old_min, old_max, old_min_rt;
int result;
guard(mutex)(&uclamp_mutex);
old_min = sysctl_sched_uclamp_util_min;
old_max = sysctl_sched_uclamp_util_max;
old_min_rt = sysctl_sched_uclamp_util_min_rt_default;
result = proc_dointvec(table, write, buffer, lenp, ppos);
if (result)
goto undo;
if (!write)
return 0;
if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE ||
sysctl_sched_uclamp_util_min_rt_default > SCHED_CAPACITY_SCALE) {
result = -EINVAL;
goto undo;
}
if (old_min != sysctl_sched_uclamp_util_min) {
uclamp_se_set(&uclamp_default[UCLAMP_MIN],
sysctl_sched_uclamp_util_min, false);
update_root_tg = true;
}
if (old_max != sysctl_sched_uclamp_util_max) {
uclamp_se_set(&uclamp_default[UCLAMP_MAX],
sysctl_sched_uclamp_util_max, false);
update_root_tg = true;
}
if (update_root_tg) {
static_branch_enable(&sched_uclamp_used);
uclamp_update_root_tg();
}
if (old_min_rt != sysctl_sched_uclamp_util_min_rt_default) {
static_branch_enable(&sched_uclamp_used);
uclamp_sync_util_min_rt_default();
}
/*
* We update all RUNNABLE tasks only when task groups are in use.
* Otherwise, keep it simple and do just a lazy update at each next
* task enqueue time.
*/
return 0;
undo:
sysctl_sched_uclamp_util_min = old_min;
sysctl_sched_uclamp_util_max = old_max;
sysctl_sched_uclamp_util_min_rt_default = old_min_rt;
return result;
}
#endif
static void uclamp_fork(struct task_struct *p)
{
enum uclamp_id clamp_id;
/*
* We don't need to hold task_rq_lock() when updating p->uclamp_* here
* as the task is still at its early fork stages.
*/
for_each_clamp_id(clamp_id)
p->uclamp[clamp_id].active = false;
if (likely(!p->sched_reset_on_fork))
return;
for_each_clamp_id(clamp_id) {
uclamp_se_set(&p->uclamp_req[clamp_id],
uclamp_none(clamp_id), false);
}
}
static void uclamp_post_fork(struct task_struct *p)
{
uclamp_update_util_min_rt_default(p);
}
static void __init init_uclamp_rq(struct rq *rq)
{
enum uclamp_id clamp_id;
struct uclamp_rq *uc_rq = rq->uclamp;
for_each_clamp_id(clamp_id) {
uc_rq[clamp_id] = (struct uclamp_rq) {
.value = uclamp_none(clamp_id)
};
}
rq->uclamp_flags = UCLAMP_FLAG_IDLE;
}
static void __init init_uclamp(void)
{
struct uclamp_se uc_max = {};
enum uclamp_id clamp_id;
int cpu;
for_each_possible_cpu(cpu)
init_uclamp_rq(cpu_rq(cpu));
for_each_clamp_id(clamp_id) {
uclamp_se_set(&init_task.uclamp_req[clamp_id],
uclamp_none(clamp_id), false);
}
/* System defaults allow max clamp values for both indexes */
uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
for_each_clamp_id(clamp_id) {
uclamp_default[clamp_id] = uc_max;
#ifdef CONFIG_UCLAMP_TASK_GROUP
root_task_group.uclamp_req[clamp_id] = uc_max;
root_task_group.uclamp[clamp_id] = uc_max;
#endif
}
}
#else /* !CONFIG_UCLAMP_TASK */
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
static inline void uclamp_fork(struct task_struct *p) { }
static inline void uclamp_post_fork(struct task_struct *p) { }
static inline void init_uclamp(void) { }
#endif /* CONFIG_UCLAMP_TASK */
bool sched_task_on_rq(struct task_struct *p)
{
return task_on_rq_queued(p);
}
unsigned long get_wchan(struct task_struct *p)
{
unsigned long ip = 0;
unsigned int state;
if (!p || p == current)
return 0;
/* Only get wchan if task is blocked and we can keep it that way. */
raw_spin_lock_irq(&p->pi_lock);
state = READ_ONCE(p->__state);
smp_rmb(); /* see try_to_wake_up() */
if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq)
ip = __get_wchan(p);
raw_spin_unlock_irq(&p->pi_lock);
return ip;
}
void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
if (!(flags & ENQUEUE_NOCLOCK))
update_rq_clock(rq);
if (!(flags & ENQUEUE_RESTORE)) {
sched_info_enqueue(rq, p);
psi_enqueue(p, (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED));
}
p->sched_class->enqueue_task(rq, p, flags);
/*
* Must be after ->enqueue_task() because ENQUEUE_DELAYED can clear
* ->sched_delayed.
*/
uclamp_rq_inc(rq, p);
if (sched_core_enabled(rq))
sched_core_enqueue(rq, p);
}
/*
* Must only return false when DEQUEUE_SLEEP.
*/
inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
if (sched_core_enabled(rq))
sched_core_dequeue(rq, p, flags);
if (!(flags & DEQUEUE_NOCLOCK))
update_rq_clock(rq);
if (!(flags & DEQUEUE_SAVE)) {
sched_info_dequeue(rq, p);
psi_dequeue(p, flags & DEQUEUE_SLEEP);
}
/*
* Must be before ->dequeue_task() because ->dequeue_task() can 'fail'
* and mark the task ->sched_delayed.
*/
uclamp_rq_dec(rq, p);
return p->sched_class->dequeue_task(rq, p, flags);
}
void activate_task(struct rq *rq, struct task_struct *p, int flags)
{
if (task_on_rq_migrating(p))
flags |= ENQUEUE_MIGRATED;
if (flags & ENQUEUE_MIGRATED)
sched_mm_cid_migrate_to(rq, p);
enqueue_task(rq, p, flags);
WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
ASSERT_EXCLUSIVE_WRITER(p->on_rq);
}
void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
SCHED_WARN_ON(flags & DEQUEUE_SLEEP);
WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
ASSERT_EXCLUSIVE_WRITER(p->on_rq);
/*
* Code explicitly relies on TASK_ON_RQ_MIGRATING begin set *before*
* dequeue_task() and cleared *after* enqueue_task().
*/
dequeue_task(rq, p, flags);
}
static void block_task(struct rq *rq, struct task_struct *p, int flags)
{
if (dequeue_task(rq, p, DEQUEUE_SLEEP | flags))
__block_task(rq, p);
}
/**
* task_curr - is this task currently executing on a CPU?
* @p: the task in question.
*
* Return: 1 if the task is currently executing. 0 otherwise.
*/
inline int task_curr(const struct task_struct *p)
{
return cpu_curr(task_cpu(p)) == p;
}
/*
* ->switching_to() is called with the pi_lock and rq_lock held and must not
* mess with locking.
*/
void check_class_changing(struct rq *rq, struct task_struct *p,
const struct sched_class *prev_class)
{
if (prev_class != p->sched_class && p->sched_class->switching_to)
p->sched_class->switching_to(rq, p);
}
/*
* switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
* use the balance_callback list if you want balancing.
*
* this means any call to check_class_changed() must be followed by a call to
* balance_callback().
*/
void check_class_changed(struct rq *rq, struct task_struct *p,
const struct sched_class *prev_class,
int oldprio)
{
if (prev_class != p->sched_class) {
if (prev_class->switched_from)
prev_class->switched_from(rq, p);
p->sched_class->switched_to(rq, p);
} else if (oldprio != p->prio || dl_task(p))
p->sched_class->prio_changed(rq, p, oldprio);
}
void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags)
{
if (p->sched_class == rq->curr->sched_class)
rq->curr->sched_class->wakeup_preempt(rq, p, flags);
else if (sched_class_above(p->sched_class, rq->curr->sched_class))
resched_curr(rq);
/*
* A queue event has occurred, and we're going to schedule. In
* this case, we can save a useless back to back clock update.
*/
if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
rq_clock_skip_update(rq);
}
static __always_inline
int __task_state_match(struct task_struct *p, unsigned int state)
{
if (READ_ONCE(p->__state) & state)
return 1;
if (READ_ONCE(p->saved_state) & state)
return -1;
return 0;
}
static __always_inline
int task_state_match(struct task_struct *p, unsigned int state)
{
/*
* Serialize against current_save_and_set_rtlock_wait_state(),
* current_restore_rtlock_saved_state(), and __refrigerator().
*/
guard(raw_spinlock_irq)(&p->pi_lock);
return __task_state_match(p, state);
}
/*
* wait_task_inactive - wait for a thread to unschedule.
*
* Wait for the thread to block in any of the states set in @match_state.
* If it changes, i.e. @p might have woken up, then return zero. When we
* succeed in waiting for @p to be off its CPU, we return a positive number
* (its total switch count). If a second call a short while later returns the
* same number, the caller can be sure that @p has remained unscheduled the
* whole time.
*
* The caller must ensure that the task *will* unschedule sometime soon,
* else this function might spin for a *long* time. This function can't
* be called with interrupts off, or it may introduce deadlock with
* smp_call_function() if an IPI is sent by the same process we are
* waiting to become inactive.
*/
unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
{
int running, queued, match;
struct rq_flags rf;
unsigned long ncsw;
struct rq *rq;
for (;;) {
/*
* We do the initial early heuristics without holding
* any task-queue locks at all. We'll only try to get
* the runqueue lock when things look like they will
* work out!
*/
rq = task_rq(p);
/*
* If the task is actively running on another CPU
* still, just relax and busy-wait without holding
* any locks.
*
* NOTE! Since we don't hold any locks, it's not
* even sure that "rq" stays as the right runqueue!
* But we don't care, since "task_on_cpu()" will
* return false if the runqueue has changed and p
* is actually now running somewhere else!
*/
while (task_on_cpu(rq, p)) {
if (!task_state_match(p, match_state))
return 0;
cpu_relax();
}
/*
* Ok, time to look more closely! We need the rq
* lock now, to be *sure*. If we're wrong, we'll
* just go back and repeat.
*/
rq = task_rq_lock(p, &rf);
trace_sched_wait_task(p);
running = task_on_cpu(rq, p);
queued = task_on_rq_queued(p);
ncsw = 0;
if ((match = __task_state_match(p, match_state))) {
/*
* When matching on p->saved_state, consider this task
* still queued so it will wait.
*/
if (match < 0)
queued = 1;
ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
}
task_rq_unlock(rq, p, &rf);
/*
* If it changed from the expected state, bail out now.
*/
if (unlikely(!ncsw))
break;
/*
* Was it really running after all now that we
* checked with the proper locks actually held?
*
* Oops. Go back and try again..
*/
if (unlikely(running)) {
cpu_relax();
continue;
}
/*
* It's not enough that it's not actively running,
* it must be off the runqueue _entirely_, and not
* preempted!
*
* So if it was still runnable (but just not actively
* running right now), it's preempted, and we should
* yield - it could be a while.
*/
if (unlikely(queued)) {
ktime_t to = NSEC_PER_SEC / HZ;
set_current_state(TASK_UNINTERRUPTIBLE);
schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
continue;
}
/*
* Ahh, all good. It wasn't running, and it wasn't
* runnable, which means that it will never become
* running in the future either. We're all done!
*/
break;
}
return ncsw;
}
#ifdef CONFIG_SMP
static void
__do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx);
static void migrate_disable_switch(struct rq *rq, struct task_struct *p)
{
struct affinity_context ac = {
.new_mask = cpumask_of(rq->cpu),
.flags = SCA_MIGRATE_DISABLE,
};
if (likely(!p->migration_disabled))
return;
if (p->cpus_ptr != &p->cpus_mask)
return;
/*
* Violates locking rules! See comment in __do_set_cpus_allowed().
*/
__do_set_cpus_allowed(p, &ac);
}
void migrate_disable(void)
{
struct task_struct *p = current;
if (p->migration_disabled) {
#ifdef CONFIG_DEBUG_PREEMPT
/*
*Warn about overflow half-way through the range.
*/
WARN_ON_ONCE((s16)p->migration_disabled < 0);
#endif
p->migration_disabled++;
return;
}
guard(preempt)();
this_rq()->nr_pinned++;
p->migration_disabled = 1;
}
EXPORT_SYMBOL_GPL(migrate_disable);
void migrate_enable(void)
{
struct task_struct *p = current;
struct affinity_context ac = {
.new_mask = &p->cpus_mask,
.flags = SCA_MIGRATE_ENABLE,
};
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Check both overflow from migrate_disable() and superfluous
* migrate_enable().
*/
if (WARN_ON_ONCE((s16)p->migration_disabled <= 0))
return;
#endif
if (p->migration_disabled > 1) {
p->migration_disabled--;
return;
}
/*
* Ensure stop_task runs either before or after this, and that
* __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().
*/
guard(preempt)();
if (p->cpus_ptr != &p->cpus_mask)
__set_cpus_allowed_ptr(p, &ac);
/*
* Mustn't clear migration_disabled() until cpus_ptr points back at the
* regular cpus_mask, otherwise things that race (eg.
* select_fallback_rq) get confused.
*/
barrier();
p->migration_disabled = 0;
this_rq()->nr_pinned--;
}
EXPORT_SYMBOL_GPL(migrate_enable);
static inline bool rq_has_pinned_tasks(struct rq *rq)
{
return rq->nr_pinned;
}
/*
* Per-CPU kthreads are allowed to run on !active && online CPUs, see
* __set_cpus_allowed_ptr() and select_fallback_rq().
*/
static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
{
/* When not in the task's cpumask, no point in looking further. */
if (!task_allowed_on_cpu(p, cpu))
return false;
/* migrate_disabled() must be allowed to finish. */
if (is_migration_disabled(p))
return cpu_online(cpu);
/* Non kernel threads are not allowed during either online or offline. */
if (!(p->flags & PF_KTHREAD))
return cpu_active(cpu);
/* KTHREAD_IS_PER_CPU is always allowed. */
if (kthread_is_per_cpu(p))
return cpu_online(cpu);
/* Regular kernel threads don't get to stay during offline. */
if (cpu_dying(cpu))
return false;
/* But are allowed during online. */
return cpu_online(cpu);
}
/*
* This is how migration works:
*
* 1) we invoke migration_cpu_stop() on the target CPU using
* stop_one_cpu().
* 2) stopper starts to run (implicitly forcing the migrated thread
* off the CPU)
* 3) it checks whether the migrated task is still in the wrong runqueue.
* 4) if it's in the wrong runqueue then the migration thread removes
* it and puts it into the right queue.
* 5) stopper completes and stop_one_cpu() returns and the migration
* is done.
*/
/*
* move_queued_task - move a queued task to new rq.
*
* Returns (locked) new rq. Old rq's lock is released.
*/
static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
struct task_struct *p, int new_cpu)
{
lockdep_assert_rq_held(rq);
deactivate_task(rq, p, DEQUEUE_NOCLOCK);
set_task_cpu(p, new_cpu);
rq_unlock(rq, rf);
rq = cpu_rq(new_cpu);
rq_lock(rq, rf);
WARN_ON_ONCE(task_cpu(p) != new_cpu);
activate_task(rq, p, 0);
wakeup_preempt(rq, p, 0);
return rq;
}
struct migration_arg {
struct task_struct *task;
int dest_cpu;
struct set_affinity_pending *pending;
};
/*
* @refs: number of wait_for_completion()
* @stop_pending: is @stop_work in use
*/
struct set_affinity_pending {
refcount_t refs;
unsigned int stop_pending;
struct completion done;
struct cpu_stop_work stop_work;
struct migration_arg arg;
};
/*
* Move (not current) task off this CPU, onto the destination CPU. We're doing
* this because either it can't run here any more (set_cpus_allowed()
* away from this CPU, or CPU going down), or because we're
* attempting to rebalance this task on exec (sched_exec).
*
* So we race with normal scheduler movements, but that's OK, as long
* as the task is no longer on this CPU.
*/
static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
struct task_struct *p, int dest_cpu)
{
/* Affinity changed (again). */
if (!is_cpu_allowed(p, dest_cpu))
return rq;
rq = move_queued_task(rq, rf, p, dest_cpu);
return rq;
}
/*
* migration_cpu_stop - this will be executed by a high-prio stopper thread
* and performs thread migration by bumping thread off CPU then
* 'pushing' onto another runqueue.
*/
static int migration_cpu_stop(void *data)
{
struct migration_arg *arg = data;
struct set_affinity_pending *pending = arg->pending;
struct task_struct *p = arg->task;
struct rq *rq = this_rq();
bool complete = false;
struct rq_flags rf;
/*
* The original target CPU might have gone down and we might
* be on another CPU but it doesn't matter.
*/
local_irq_save(rf.flags);
/*
* We need to explicitly wake pending tasks before running
* __migrate_task() such that we will not miss enforcing cpus_ptr
* during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
*/
flush_smp_call_function_queue();
raw_spin_lock(&p->pi_lock);
rq_lock(rq, &rf);
/*
* If we were passed a pending, then ->stop_pending was set, thus
* p->migration_pending must have remained stable.
*/
WARN_ON_ONCE(pending && pending != p->migration_pending);
/*
* If task_rq(p) != rq, it cannot be migrated here, because we're
* holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
* we're holding p->pi_lock.
*/
if (task_rq(p) == rq) {
if (is_migration_disabled(p))
goto out;
if (pending) {
p->migration_pending = NULL;
complete = true;
if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
goto out;
}
if (task_on_rq_queued(p)) {
update_rq_clock(rq);
rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
} else {
p->wake_cpu = arg->dest_cpu;
}
/*
* XXX __migrate_task() can fail, at which point we might end
* up running on a dodgy CPU, AFAICT this can only happen
* during CPU hotplug, at which point we'll get pushed out
* anyway, so it's probably not a big deal.
*/
} else if (pending) {
/*
* This happens when we get migrated between migrate_enable()'s
* preempt_enable() and scheduling the stopper task. At that
* point we're a regular task again and not current anymore.
*
* A !PREEMPT kernel has a giant hole here, which makes it far
* more likely.
*/
/*
* The task moved before the stopper got to run. We're holding
* ->pi_lock, so the allowed mask is stable - if it got
* somewhere allowed, we're done.
*/
if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
p->migration_pending = NULL;
complete = true;
goto out;
}
/*
* When migrate_enable() hits a rq mis-match we can't reliably
* determine is_migration_disabled() and so have to chase after
* it.
*/
WARN_ON_ONCE(!pending->stop_pending);
preempt_disable();
task_rq_unlock(rq, p, &rf);
stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
&pending->arg, &pending->stop_work);
preempt_enable();
return 0;
}
out:
if (pending)
pending->stop_pending = false;
task_rq_unlock(rq, p, &rf);
if (complete)
complete_all(&pending->done);
return 0;
}
int push_cpu_stop(void *arg)
{
struct rq *lowest_rq = NULL, *rq = this_rq();
struct task_struct *p = arg;
raw_spin_lock_irq(&p->pi_lock);
raw_spin_rq_lock(rq);
if (task_rq(p) != rq)
goto out_unlock;
if (is_migration_disabled(p)) {
p->migration_flags |= MDF_PUSH;
goto out_unlock;
}
p->migration_flags &= ~MDF_PUSH;
if (p->sched_class->find_lock_rq)
lowest_rq = p->sched_class->find_lock_rq(p, rq);
if (!lowest_rq)
goto out_unlock;
// XXX validate p is still the highest prio task
if (task_rq(p) == rq) {
deactivate_task(rq, p, 0);
set_task_cpu(p, lowest_rq->cpu);
activate_task(lowest_rq, p, 0);
resched_curr(lowest_rq);
}
double_unlock_balance(rq, lowest_rq);
out_unlock:
rq->push_busy = false;
raw_spin_rq_unlock(rq);
raw_spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
return 0;
}
/*
* sched_class::set_cpus_allowed must do the below, but is not required to
* actually call this function.
*/
void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx)
{
if (ctx->flags & (SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) {
p->cpus_ptr = ctx->new_mask;
return;
}
cpumask_copy(&p->cpus_mask, ctx->new_mask);
p->nr_cpus_allowed = cpumask_weight(ctx->new_mask);
/*
* Swap in a new user_cpus_ptr if SCA_USER flag set
*/
if (ctx->flags & SCA_USER)
swap(p->user_cpus_ptr, ctx->user_mask);
}
static void
__do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
{
struct rq *rq = task_rq(p);
bool queued, running;
/*
* This here violates the locking rules for affinity, since we're only
* supposed to change these variables while holding both rq->lock and
* p->pi_lock.
*
* HOWEVER, it magically works, because ttwu() is the only code that
* accesses these variables under p->pi_lock and only does so after
* smp_cond_load_acquire(&p->on_cpu, !VAL), and we're in __schedule()
* before finish_task().
*
* XXX do further audits, this smells like something putrid.
*/
if (ctx->flags & SCA_MIGRATE_DISABLE)
SCHED_WARN_ON(!p->on_cpu);
else
lockdep_assert_held(&p->pi_lock);
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued) {
/*
* Because __kthread_bind() calls this on blocked tasks without
* holding rq->lock.
*/
lockdep_assert_rq_held(rq);
dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
}
if (running)
put_prev_task(rq, p);
p->sched_class->set_cpus_allowed(p, ctx);
if (queued)
enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
if (running)
set_next_task(rq, p);
}
/*
* Used for kthread_bind() and select_fallback_rq(), in both cases the user
* affinity (if any) should be destroyed too.
*/
void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
struct affinity_context ac = {
.new_mask = new_mask,
.user_mask = NULL,
.flags = SCA_USER, /* clear the user requested mask */
};
union cpumask_rcuhead {
cpumask_t cpumask;
struct rcu_head rcu;
};
__do_set_cpus_allowed(p, &ac);
/*
* Because this is called with p->pi_lock held, it is not possible
* to use kfree() here (when PREEMPT_RT=y), therefore punt to using
* kfree_rcu().
*/
kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu);
}
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
int node)
{
cpumask_t *user_mask;
unsigned long flags;
/*
* Always clear dst->user_cpus_ptr first as their user_cpus_ptr's
* may differ by now due to racing.
*/
dst->user_cpus_ptr = NULL;
/*
* This check is racy and losing the race is a valid situation.
* It is not worth the extra overhead of taking the pi_lock on
* every fork/clone.
*/
if (data_race(!src->user_cpus_ptr))
return 0;
user_mask = alloc_user_cpus_ptr(node);
if (!user_mask)
return -ENOMEM;
/*
* Use pi_lock to protect content of user_cpus_ptr
*
* Though unlikely, user_cpus_ptr can be reset to NULL by a concurrent
* do_set_cpus_allowed().
*/
raw_spin_lock_irqsave(&src->pi_lock, flags);
if (src->user_cpus_ptr) {
swap(dst->user_cpus_ptr, user_mask);
cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
}
raw_spin_unlock_irqrestore(&src->pi_lock, flags);
if (unlikely(user_mask))
kfree(user_mask);
return 0;
}
static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
{
struct cpumask *user_mask = NULL;
swap(p->user_cpus_ptr, user_mask);
return user_mask;
}
void release_user_cpus_ptr(struct task_struct *p)
{
kfree(clear_user_cpus_ptr(p));
}
/*
* This function is wildly self concurrent; here be dragons.
*
*
* When given a valid mask, __set_cpus_allowed_ptr() must block until the
* designated task is enqueued on an allowed CPU. If that task is currently
* running, we have to kick it out using the CPU stopper.
*
* Migrate-Disable comes along and tramples all over our nice sandcastle.
* Consider:
*
* Initial conditions: P0->cpus_mask = [0, 1]
*
* P0@CPU0 P1
*
* migrate_disable();
* <preempted>
* set_cpus_allowed_ptr(P0, [1]);
*
* P1 *cannot* return from this set_cpus_allowed_ptr() call until P0 executes
* its outermost migrate_enable() (i.e. it exits its Migrate-Disable region).
* This means we need the following scheme:
*
* P0@CPU0 P1
*
* migrate_disable();
* <preempted>
* set_cpus_allowed_ptr(P0, [1]);
* <blocks>
* <resumes>
* migrate_enable();
* __set_cpus_allowed_ptr();
* <wakes local stopper>
* `--> <woken on migration completion>
*
* Now the fun stuff: there may be several P1-like tasks, i.e. multiple
* concurrent set_cpus_allowed_ptr(P0, [*]) calls. CPU affinity changes of any
* task p are serialized by p->pi_lock, which we can leverage: the one that
* should come into effect at the end of the Migrate-Disable region is the last
* one. This means we only need to track a single cpumask (i.e. p->cpus_mask),
* but we still need to properly signal those waiting tasks at the appropriate
* moment.
*
* This is implemented using struct set_affinity_pending. The first
* __set_cpus_allowed_ptr() caller within a given Migrate-Disable region will
* setup an instance of that struct and install it on the targeted task_struct.
* Any and all further callers will reuse that instance. Those then wait for
* a completion signaled at the tail of the CPU stopper callback (1), triggered
* on the end of the Migrate-Disable region (i.e. outermost migrate_enable()).
*
*
* (1) In the cases covered above. There is one more where the completion is
* signaled within affine_move_task() itself: when a subsequent affinity request
* occurs after the stopper bailed out due to the targeted task still being
* Migrate-Disable. Consider:
*
* Initial conditions: P0->cpus_mask = [0, 1]
*
* CPU0 P1 P2
* <P0>
* migrate_disable();
* <preempted>
* set_cpus_allowed_ptr(P0, [1]);
* <blocks>
* <migration/0>
* migration_cpu_stop()
* is_migration_disabled()
* <bails>
* set_cpus_allowed_ptr(P0, [0, 1]);
* <signal completion>
* <awakes>
*
* Note that the above is safe vs a concurrent migrate_enable(), as any
* pending affinity completion is preceded by an uninstallation of
* p->migration_pending done with p->pi_lock held.
*/
static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flags *rf,
int dest_cpu, unsigned int flags)
__releases(rq->lock)
__releases(p->pi_lock)
{
struct set_affinity_pending my_pending = { }, *pending = NULL;
bool stop_pending, complete = false;
/* Can the task run on the task's current CPU? If so, we're done */
if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
struct task_struct *push_task = NULL;
if ((flags & SCA_MIGRATE_ENABLE) &&
(p->migration_flags & MDF_PUSH) && !rq->push_busy) {
rq->push_busy = true;
push_task = get_task_struct(p);
}
/*
* If there are pending waiters, but no pending stop_work,
* then complete now.
*/
pending = p->migration_pending;
if (pending && !pending->stop_pending) {
p->migration_pending = NULL;
complete = true;
}
preempt_disable();
task_rq_unlock(rq, p, rf);
if (push_task) {
stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
p, &rq->push_work);
}
preempt_enable();
if (complete)
complete_all(&pending->done);
return 0;
}
if (!(flags & SCA_MIGRATE_ENABLE)) {
/* serialized by p->pi_lock */
if (!p->migration_pending) {
/* Install the request */
refcount_set(&my_pending.refs, 1);
init_completion(&my_pending.done);
my_pending.arg = (struct migration_arg) {
.task = p,
.dest_cpu = dest_cpu,
.pending = &my_pending,
};
p->migration_pending = &my_pending;
} else {
pending = p->migration_pending;
refcount_inc(&pending->refs);
/*
* Affinity has changed, but we've already installed a
* pending. migration_cpu_stop() *must* see this, else
* we risk a completion of the pending despite having a
* task on a disallowed CPU.
*
* Serialized by p->pi_lock, so this is safe.
*/
pending->arg.dest_cpu = dest_cpu;
}
}
pending = p->migration_pending;
/*
* - !MIGRATE_ENABLE:
* we'll have installed a pending if there wasn't one already.
*
* - MIGRATE_ENABLE:
* we're here because the current CPU isn't matching anymore,
* the only way that can happen is because of a concurrent
* set_cpus_allowed_ptr() call, which should then still be
* pending completion.
*
* Either way, we really should have a @pending here.
*/
if (WARN_ON_ONCE(!pending)) {
task_rq_unlock(rq, p, rf);
return -EINVAL;
}
if (task_on_cpu(rq, p) || READ_ONCE(p->__state) == TASK_WAKING) {
/*
* MIGRATE_ENABLE gets here because 'p == current', but for
* anything else we cannot do is_migration_disabled(), punt
* and have the stopper function handle it all race-free.
*/
stop_pending = pending->stop_pending;
if (!stop_pending)
pending->stop_pending = true;
if (flags & SCA_MIGRATE_ENABLE)
p->migration_flags &= ~MDF_PUSH;
preempt_disable();
task_rq_unlock(rq, p, rf);
if (!stop_pending) {
stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
&pending->arg, &pending->stop_work);
}
preempt_enable();
if (flags & SCA_MIGRATE_ENABLE)
return 0;
} else {
if (!is_migration_disabled(p)) {
if (task_on_rq_queued(p))
rq = move_queued_task(rq, rf, p, dest_cpu);
if (!pending->stop_pending) {
p->migration_pending = NULL;
complete = true;
}
}
task_rq_unlock(rq, p, rf);
if (complete)
complete_all(&pending->done);
}
wait_for_completion(&pending->done);
if (refcount_dec_and_test(&pending->refs))
wake_up_var(&pending->refs); /* No UaF, just an address */
/*
* Block the original owner of &pending until all subsequent callers
* have seen the completion and decremented the refcount
*/
wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));
/* ARGH */
WARN_ON_ONCE(my_pending.stop_pending);
return 0;
}
/*
* Called with both p->pi_lock and rq->lock held; drops both before returning.
*/
static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
struct affinity_context *ctx,
struct rq *rq,
struct rq_flags *rf)
__releases(rq->lock)
__releases(p->pi_lock)
{
const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
const struct cpumask *cpu_valid_mask = cpu_active_mask;
bool kthread = p->flags & PF_KTHREAD;
unsigned int dest_cpu;
int ret = 0;
update_rq_clock(rq);
if (kthread || is_migration_disabled(p)) {
/*
* Kernel threads are allowed on online && !active CPUs,
* however, during cpu-hot-unplug, even these might get pushed
* away if not KTHREAD_IS_PER_CPU.
*
* Specifically, migration_disabled() tasks must not fail the
* cpumask_any_and_distribute() pick below, esp. so on
* SCA_MIGRATE_ENABLE, otherwise we'll not call
* set_cpus_allowed_common() and actually reset p->cpus_ptr.
*/
cpu_valid_mask = cpu_online_mask;
}
if (!kthread && !cpumask_subset(ctx->new_mask, cpu_allowed_mask)) {
ret = -EINVAL;
goto out;
}
/*
* Must re-check here, to close a race against __kthread_bind(),
* sched_setaffinity() is not guaranteed to observe the flag.
*/
if ((ctx->flags & SCA_CHECK) && (p->flags & PF_NO_SETAFFINITY)) {
ret = -EINVAL;
goto out;
}
if (!(ctx->flags & SCA_MIGRATE_ENABLE)) {
if (cpumask_equal(&p->cpus_mask, ctx->new_mask)) {
if (ctx->flags & SCA_USER)
swap(p->user_cpus_ptr, ctx->user_mask);
goto out;
}
if (WARN_ON_ONCE(p == current &&
is_migration_disabled(p) &&
!cpumask_test_cpu(task_cpu(p), ctx->new_mask))) {
ret = -EBUSY;
goto out;
}
}
/*
* Picking a ~random cpu helps in cases where we are changing affinity
* for groups of tasks (ie. cpuset), so that load balancing is not
* immediately required to distribute the tasks within their new mask.
*/
dest_cpu = cpumask_any_and_distribute(cpu_valid_mask, ctx->new_mask);
if (dest_cpu >= nr_cpu_ids) {
ret = -EINVAL;
goto out;
}
__do_set_cpus_allowed(p, ctx);
return affine_move_task(rq, p, rf, dest_cpu, ctx->flags);
out:
task_rq_unlock(rq, p, rf);
return ret;
}
/*
* Change a given task's CPU affinity. Migrate the thread to a
* proper CPU and schedule it away if the CPU it's executing on
* is removed from the allowed bitmask.
*
* NOTE: the caller must have a valid reference to the task, the
* task must not exit() & deallocate itself prematurely. The
* call is not atomic; no spinlocks may be held.
*/
int __set_cpus_allowed_ptr(struct task_struct *p, struct affinity_context *ctx)
{
struct rq_flags rf;
struct rq *rq;
rq = task_rq_lock(p, &rf);
/*
* Masking should be skipped if SCA_USER or any of the SCA_MIGRATE_*
* flags are set.
*/
if (p->user_cpus_ptr &&
!(ctx->flags & (SCA_USER | SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) &&
cpumask_and(rq->scratch_mask, ctx->new_mask, p->user_cpus_ptr))
ctx->new_mask = rq->scratch_mask;
return __set_cpus_allowed_ptr_locked(p, ctx, rq, &rf);
}
int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
struct affinity_context ac = {
.new_mask = new_mask,
.flags = 0,
};
return __set_cpus_allowed_ptr(p, &ac);
}
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
/*
* Change a given task's CPU affinity to the intersection of its current
* affinity mask and @subset_mask, writing the resulting mask to @new_mask.
* If user_cpus_ptr is defined, use it as the basis for restricting CPU
* affinity or use cpu_online_mask instead.
*
* If the resulting mask is empty, leave the affinity unchanged and return
* -EINVAL.
*/
static int restrict_cpus_allowed_ptr(struct task_struct *p,
struct cpumask *new_mask,
const struct cpumask *subset_mask)
{
struct affinity_context ac = {
.new_mask = new_mask,
.flags = 0,
};
struct rq_flags rf;
struct rq *rq;
int err;
rq = task_rq_lock(p, &rf);
/*
* Forcefully restricting the affinity of a deadline task is
* likely to cause problems, so fail and noisily override the
* mask entirely.
*/
if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
err = -EPERM;
goto err_unlock;
}
if (!cpumask_and(new_mask, task_user_cpus(p), subset_mask)) {
err = -EINVAL;
goto err_unlock;
}
return __set_cpus_allowed_ptr_locked(p, &ac, rq, &rf);
err_unlock:
task_rq_unlock(rq, p, &rf);
return err;
}
/*
* Restrict the CPU affinity of task @p so that it is a subset of
* task_cpu_possible_mask() and point @p->user_cpus_ptr to a copy of the
* old affinity mask. If the resulting mask is empty, we warn and walk
* up the cpuset hierarchy until we find a suitable mask.
*/
void force_compatible_cpus_allowed_ptr(struct task_struct *p)
{
cpumask_var_t new_mask;
const struct cpumask *override_mask = task_cpu_possible_mask(p);
alloc_cpumask_var(&new_mask, GFP_KERNEL);
/*
* __migrate_task() can fail silently in the face of concurrent
* offlining of the chosen destination CPU, so take the hotplug
* lock to ensure that the migration succeeds.
*/
cpus_read_lock();
if (!cpumask_available(new_mask))
goto out_set_mask;
if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
goto out_free_mask;
/*
* We failed to find a valid subset of the affinity mask for the
* task, so override it based on its cpuset hierarchy.
*/
cpuset_cpus_allowed(p, new_mask);
override_mask = new_mask;
out_set_mask:
if (printk_ratelimit()) {
printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
task_pid_nr(p), p->comm,
cpumask_pr_args(override_mask));
}
WARN_ON(set_cpus_allowed_ptr(p, override_mask));
out_free_mask:
cpus_read_unlock();
free_cpumask_var(new_mask);
}
/*
* Restore the affinity of a task @p which was previously restricted by a
* call to force_compatible_cpus_allowed_ptr().
*
* It is the caller's responsibility to serialise this with any calls to
* force_compatible_cpus_allowed_ptr(@p).
*/
void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
{
struct affinity_context ac = {
.new_mask = task_user_cpus(p),
.flags = 0,
};
int ret;
/*
* Try to restore the old affinity mask with __sched_setaffinity().
* Cpuset masking will be done there too.
*/
ret = __sched_setaffinity(p, &ac);
WARN_ON_ONCE(ret);
}
void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
#ifdef CONFIG_SCHED_DEBUG
unsigned int state = READ_ONCE(p->__state);
/*
* We should never call set_task_cpu() on a blocked task,
* ttwu() will sort out the placement.
*/
WARN_ON_ONCE(state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq);
/*
* Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
* because schedstat_wait_{start,end} rebase migrating task's wait_start
* time relying on p->on_rq.
*/
WARN_ON_ONCE(state == TASK_RUNNING &&
p->sched_class == &fair_sched_class &&
(p->on_rq && !task_on_rq_migrating(p)));
#ifdef CONFIG_LOCKDEP
/*
* The caller should hold either p->pi_lock or rq->lock, when changing
* a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
*
* sched_move_task() holds both and thus holding either pins the cgroup,
* see task_group().
*
* Furthermore, all task_rq users should acquire both locks, see
* task_rq_lock().
*/
WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
lockdep_is_held(__rq_lockp(task_rq(p)))));
#endif
/*
* Clearly, migrating tasks to offline CPUs is a fairly daft thing.
*/
WARN_ON_ONCE(!cpu_online(new_cpu));
WARN_ON_ONCE(is_migration_disabled(p));
#endif
trace_sched_migrate_task(p, new_cpu);
if (task_cpu(p) != new_cpu) {
if (p->sched_class->migrate_task_rq)
p->sched_class->migrate_task_rq(p, new_cpu);
p->se.nr_migrations++;
rseq_migrate(p);
sched_mm_cid_migrate_from(p);
perf_event_task_migrate(p);
}
__set_task_cpu(p, new_cpu);
}
#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
if (task_on_rq_queued(p)) {
struct rq *src_rq, *dst_rq;
struct rq_flags srf, drf;
src_rq = task_rq(p);
dst_rq = cpu_rq(cpu);
rq_pin_lock(src_rq, &srf);
rq_pin_lock(dst_rq, &drf);
deactivate_task(src_rq, p, 0);
set_task_cpu(p, cpu);
activate_task(dst_rq, p, 0);
wakeup_preempt(dst_rq, p, 0);
rq_unpin_lock(dst_rq, &drf);
rq_unpin_lock(src_rq, &srf);
} else {
/*
* Task isn't running anymore; make it appear like we migrated
* it before it went to sleep. This means on wakeup we make the
* previous CPU our target instead of where it really is.
*/
p->wake_cpu = cpu;
}
}
struct migration_swap_arg {
struct task_struct *src_task, *dst_task;
int src_cpu, dst_cpu;
};
static int migrate_swap_stop(void *data)
{
struct migration_swap_arg *arg = data;
struct rq *src_rq, *dst_rq;
if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
return -EAGAIN;
src_rq = cpu_rq(arg->src_cpu);
dst_rq = cpu_rq(arg->dst_cpu);
guard(double_raw_spinlock)(&arg->src_task->pi_lock, &arg->dst_task->pi_lock);
guard(double_rq_lock)(src_rq, dst_rq);
if (task_cpu(arg->dst_task) != arg->dst_cpu)
return -EAGAIN;
if (task_cpu(arg->src_task) != arg->src_cpu)
return -EAGAIN;
if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
return -EAGAIN;
if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
return -EAGAIN;
__migrate_swap_task(arg->src_task, arg->dst_cpu);
__migrate_swap_task(arg->dst_task, arg->src_cpu);
return 0;
}
/*
* Cross migrate two tasks
*/
int migrate_swap(struct task_struct *cur, struct task_struct *p,
int target_cpu, int curr_cpu)
{
struct migration_swap_arg arg;
int ret = -EINVAL;
arg = (struct migration_swap_arg){
.src_task = cur,
.src_cpu = curr_cpu,
.dst_task = p,
.dst_cpu = target_cpu,
};
if (arg.src_cpu == arg.dst_cpu)
goto out;
/*
* These three tests are all lockless; this is OK since all of them
* will be re-checked with proper locks held further down the line.
*/
if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
goto out;
if (!cpumask_test_cpu(arg.dst_cpu, arg.src_task->cpus_ptr))
goto out;
if (!cpumask_test_cpu(arg.src_cpu, arg.dst_task->cpus_ptr))
goto out;
trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);
out:
return ret;
}
#endif /* CONFIG_NUMA_BALANCING */
/***
* kick_process - kick a running thread to enter/exit the kernel
* @p: the to-be-kicked thread
*
* Cause a process which is running on another CPU to enter
* kernel-mode, without any delay. (to get signals handled.)
*
* NOTE: this function doesn't have to take the runqueue lock,
* because all it wants to ensure is that the remote task enters
* the kernel. If the IPI races and the task has been migrated
* to another CPU then no harm is done and the purpose has been
* achieved as well.
*/
void kick_process(struct task_struct *p)
{
guard(preempt)();
int cpu = task_cpu(p);
if ((cpu != smp_processor_id()) && task_curr(p))
smp_send_reschedule(cpu);
}
EXPORT_SYMBOL_GPL(kick_process);
/*
* ->cpus_ptr is protected by both rq->lock and p->pi_lock
*
* A few notes on cpu_active vs cpu_online:
*
* - cpu_active must be a subset of cpu_online
*
* - on CPU-up we allow per-CPU kthreads on the online && !active CPU,
* see __set_cpus_allowed_ptr(). At this point the newly online
* CPU isn't yet part of the sched domains, and balancing will not
* see it.
*
* - on CPU-down we clear cpu_active() to mask the sched domains and
* avoid the load balancer to place new tasks on the to be removed
* CPU. Existing tasks will remain running there and will be taken
* off.
*
* This means that fallback selection must not select !active CPUs.
* And can assume that any active CPU must be online. Conversely
* select_task_rq() below may allow selection of !active CPUs in order
* to satisfy the above rules.
*/
static int select_fallback_rq(int cpu, struct task_struct *p)
{
int nid = cpu_to_node(cpu);
const struct cpumask *nodemask = NULL;
enum { cpuset, possible, fail } state = cpuset;
int dest_cpu;
/*
* If the node that the CPU is on has been offlined, cpu_to_node()
* will return -1. There is no CPU on the node, and we should
* select the CPU on the other node.
*/
if (nid != -1) {
nodemask = cpumask_of_node(nid);
/* Look for allowed, online CPU in same node. */
for_each_cpu(dest_cpu, nodemask) {
if (is_cpu_allowed(p, dest_cpu))
return dest_cpu;
}
}
for (;;) {
/* Any allowed, online CPU? */
for_each_cpu(dest_cpu, p->cpus_ptr) {
if (!is_cpu_allowed(p, dest_cpu))
continue;
goto out;
}
/* No more Mr. Nice Guy. */
switch (state) {
case cpuset:
if (cpuset_cpus_allowed_fallback(p)) {
state = possible;
break;
}
fallthrough;
case possible:
/*
* XXX When called from select_task_rq() we only
* hold p->pi_lock and again violate locking order.
*
* More yuck to audit.
*/
do_set_cpus_allowed(p, task_cpu_possible_mask(p));
state = fail;
break;
case fail:
BUG();
break;
}
}
out:
if (state != cpuset) {
/*
* Don't tell them about moving exiting tasks or
* kernel threads (both mm NULL), since they never
* leave kernel.
*/
if (p->mm && printk_ratelimit()) {
printk_deferred("process %d (%s) no longer affine to cpu%d\n",
task_pid_nr(p), p->comm, cpu);
}
}
return dest_cpu;
}
/*
* The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable.
*/
static inline
int select_task_rq(struct task_struct *p, int cpu, int wake_flags)
{
lockdep_assert_held(&p->pi_lock);
if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))
cpu = p->sched_class->select_task_rq(p, cpu, wake_flags);
else
cpu = cpumask_any(p->cpus_ptr);
/*
* In order not to call set_task_cpu() on a blocking task we need
* to rely on ttwu() to place the task on a valid ->cpus_ptr
* CPU.
*
* Since this is common to all placement strategies, this lives here.
*
* [ this allows ->select_task() to simply return task_cpu(p) and
* not worry about this generic constraint ]
*/
if (unlikely(!is_cpu_allowed(p, cpu)))
cpu = select_fallback_rq(task_cpu(p), p);
return cpu;
}
void sched_set_stop_task(int cpu, struct task_struct *stop)
{
static struct lock_class_key stop_pi_lock;
struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
struct task_struct *old_stop = cpu_rq(cpu)->stop;
if (stop) {
/*
* Make it appear like a SCHED_FIFO task, its something
* userspace knows about and won't get confused about.
*
* Also, it will make PI more or less work without too
* much confusion -- but then, stop work should not
* rely on PI working anyway.
*/
sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m);
stop->sched_class = &stop_sched_class;
/*
* The PI code calls rt_mutex_setprio() with ->pi_lock held to
* adjust the effective priority of a task. As a result,
* rt_mutex_setprio() can trigger (RT) balancing operations,
* which can then trigger wakeups of the stop thread to push
* around the current task.
*
* The stop task itself will never be part of the PI-chain, it
* never blocks, therefore that ->pi_lock recursion is safe.
* Tell lockdep about this by placing the stop->pi_lock in its
* own class.
*/
lockdep_set_class(&stop->pi_lock, &stop_pi_lock);
}
cpu_rq(cpu)->stop = stop;
if (old_stop) {
/*
* Reset it back to a normal scheduling class so that
* it can die in pieces.
*/
old_stop->sched_class = &rt_sched_class;
}
}
#else /* CONFIG_SMP */
static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { }
static inline bool rq_has_pinned_tasks(struct rq *rq)
{
return false;
}
#endif /* !CONFIG_SMP */
static void
ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
{
struct rq *rq;
if (!schedstat_enabled())
return;
rq = this_rq();
#ifdef CONFIG_SMP
if (cpu == rq->cpu) {
__schedstat_inc(rq->ttwu_local);
__schedstat_inc(p->stats.nr_wakeups_local);
} else {
struct sched_domain *sd;
__schedstat_inc(p->stats.nr_wakeups_remote);
guard(rcu)();
for_each_domain(rq->cpu, sd) {
if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
__schedstat_inc(sd->ttwu_wake_remote);
break;
}
}
}
if (wake_flags & WF_MIGRATED)
__schedstat_inc(p->stats.nr_wakeups_migrate);
#endif /* CONFIG_SMP */
__schedstat_inc(rq->ttwu_count);
__schedstat_inc(p->stats.nr_wakeups);
if (wake_flags & WF_SYNC)
__schedstat_inc(p->stats.nr_wakeups_sync);
}
/*
* Mark the task runnable.
*/
static inline void ttwu_do_wakeup(struct task_struct *p)
{
WRITE_ONCE(p->__state, TASK_RUNNING);
trace_sched_wakeup(p);
}
static void
ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
struct rq_flags *rf)
{
int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;
lockdep_assert_rq_held(rq);
if (p->sched_contributes_to_load)
rq->nr_uninterruptible--;
#ifdef CONFIG_SMP
if (wake_flags & WF_MIGRATED)
en_flags |= ENQUEUE_MIGRATED;
else
#endif
if (p->in_iowait) {
delayacct_blkio_end(p);
atomic_dec(&task_rq(p)->nr_iowait);
}
activate_task(rq, p, en_flags);
wakeup_preempt(rq, p, wake_flags);
ttwu_do_wakeup(p);
#ifdef CONFIG_SMP
if (p->sched_class->task_woken) {
/*
* Our task @p is fully woken up and running; so it's safe to
* drop the rq->lock, hereafter rq is only used for statistics.
*/
rq_unpin_lock(rq, rf);
p->sched_class->task_woken(rq, p);
rq_repin_lock(rq, rf);
}
if (rq->idle_stamp) {
u64 delta = rq_clock(rq) - rq->idle_stamp;
u64 max = 2*rq->max_idle_balance_cost;
update_avg(&rq->avg_idle, delta);
if (rq->avg_idle > max)
rq->avg_idle = max;
rq->idle_stamp = 0;
}
#endif
}
/*
* Consider @p being inside a wait loop:
*
* for (;;) {
* set_current_state(TASK_UNINTERRUPTIBLE);
*
* if (CONDITION)
* break;
*
* schedule();
* }
* __set_current_state(TASK_RUNNING);
*
* between set_current_state() and schedule(). In this case @p is still
* runnable, so all that needs doing is change p->state back to TASK_RUNNING in
* an atomic manner.
*
* By taking task_rq(p)->lock we serialize against schedule(), if @p->on_rq
* then schedule() must still happen and p->state can be changed to
* TASK_RUNNING. Otherwise we lost the race, schedule() has happened, and we
* need to do a full wakeup with enqueue.
*
* Returns: %true when the wakeup is done,
* %false otherwise.
*/
static int ttwu_runnable(struct task_struct *p, int wake_flags)
{
struct rq_flags rf;
struct rq *rq;
int ret = 0;
rq = __task_rq_lock(p, &rf);
if (task_on_rq_queued(p)) {
update_rq_clock(rq);
if (p->se.sched_delayed)
enqueue_task(rq, p, ENQUEUE_NOCLOCK | ENQUEUE_DELAYED);
if (!task_on_cpu(rq, p)) {
/*
* When on_rq && !on_cpu the task is preempted, see if
* it should preempt the task that is current now.
*/
wakeup_preempt(rq, p, wake_flags);
}
ttwu_do_wakeup(p);
ret = 1;
}
__task_rq_unlock(rq, &rf);
return ret;
}
#ifdef CONFIG_SMP
void sched_ttwu_pending(void *arg)
{
struct llist_node *llist = arg;
struct rq *rq = this_rq();
struct task_struct *p, *t;
struct rq_flags rf;
if (!llist)
return;
rq_lock_irqsave(rq, &rf);
update_rq_clock(rq);
llist_for_each_entry_safe(p, t, llist, wake_entry.llist) {
if (WARN_ON_ONCE(p->on_cpu))
smp_cond_load_acquire(&p->on_cpu, !VAL);
if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
set_task_cpu(p, cpu_of(rq));
ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
}
/*
* Must be after enqueueing at least once task such that
* idle_cpu() does not observe a false-negative -- if it does,
* it is possible for select_idle_siblings() to stack a number
* of tasks on this CPU during that window.
*
* It is OK to clear ttwu_pending when another task pending.
* We will receive IPI after local IRQ enabled and then enqueue it.
* Since now nr_running > 0, idle_cpu() will always get correct result.
*/
WRITE_ONCE(rq->ttwu_pending, 0);
rq_unlock_irqrestore(rq, &rf);
}
/*
* Prepare the scene for sending an IPI for a remote smp_call
*
* Returns true if the caller can proceed with sending the IPI.
* Returns false otherwise.
*/
bool call_function_single_prep_ipi(int cpu)
{
if (set_nr_if_polling(cpu_rq(cpu)->idle)) {
trace_sched_wake_idle_without_ipi(cpu);
return false;
}
return true;
}
/*
* Queue a task on the target CPUs wake_list and wake the CPU via IPI if
* necessary. The wakee CPU on receipt of the IPI will queue the task
* via sched_ttwu_wakeup() for activation so the wakee incurs the cost
* of the wakeup instead of the waker.
*/
static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
struct rq *rq = cpu_rq(cpu);
p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
WRITE_ONCE(rq->ttwu_pending, 1);
__smp_call_single_queue(cpu, &p->wake_entry.llist);
}
void wake_up_if_idle(int cpu)
{
struct rq *rq = cpu_rq(cpu);
guard(rcu)();
if (is_idle_task(rcu_dereference(rq->curr))) {
guard(rq_lock_irqsave)(rq);
if (is_idle_task(rq->curr))
resched_curr(rq);
}
}
bool cpus_equal_capacity(int this_cpu, int that_cpu)
{
if (!sched_asym_cpucap_active())
return true;
if (this_cpu == that_cpu)
return true;
return arch_scale_cpu_capacity(this_cpu) == arch_scale_cpu_capacity(that_cpu);
}
bool cpus_share_cache(int this_cpu, int that_cpu)
{
if (this_cpu == that_cpu)
return true;
return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
}
/*
* Whether CPUs are share cache resources, which means LLC on non-cluster
* machines and LLC tag or L2 on machines with clusters.
*/
bool cpus_share_resources(int this_cpu, int that_cpu)
{
if (this_cpu == that_cpu)
return true;
return per_cpu(sd_share_id, this_cpu) == per_cpu(sd_share_id, that_cpu);
}
static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
{
/*
* The BPF scheduler may depend on select_task_rq() being invoked during
* wakeups. In addition, @p may end up executing on a different CPU
* regardless of what happens in the wakeup path making the ttwu_queue
* optimization less meaningful. Skip if on SCX.
*/
if (task_on_scx(p))
return false;
/*
* Do not complicate things with the async wake_list while the CPU is
* in hotplug state.
*/
if (!cpu_active(cpu))
return false;
/* Ensure the task will still be allowed to run on the CPU. */
if (!cpumask_test_cpu(cpu, p->cpus_ptr))
return false;
/*
* If the CPU does not share cache, then queue the task on the
* remote rqs wakelist to avoid accessing remote data.
*/
if (!cpus_share_cache(smp_processor_id(), cpu))
return true;
if (cpu == smp_processor_id())
return false;
/*
* If the wakee cpu is idle, or the task is descheduling and the
* only running task on the CPU, then use the wakelist to offload
* the task activation to the idle (or soon-to-be-idle) CPU as
* the current CPU is likely busy. nr_running is checked to
* avoid unnecessary task stacking.
*
* Note that we can only get here with (wakee) p->on_rq=0,
* p->on_cpu can be whatever, we've done the dequeue, so
* the wakee has been accounted out of ->nr_running.
*/
if (!cpu_rq(cpu)->nr_running)
return true;
return false;
}
static bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
if (sched_feat(TTWU_QUEUE) && ttwu_queue_cond(p, cpu)) {
sched_clock_cpu(cpu); /* Sync clocks across CPUs */
__ttwu_queue_wakelist(p, cpu, wake_flags);
return true;
}
return false;
}
#else /* !CONFIG_SMP */
static inline bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
return false;
}
#endif /* CONFIG_SMP */
static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
{
struct rq *rq = cpu_rq(cpu);
struct rq_flags rf;
if (ttwu_queue_wakelist(p, cpu, wake_flags))
return;
rq_lock(rq, &rf);
update_rq_clock(rq);
ttwu_do_activate(rq, p, wake_flags, &rf);
rq_unlock(rq, &rf);
}
/*
* Invoked from try_to_wake_up() to check whether the task can be woken up.
*
* The caller holds p::pi_lock if p != current or has preemption
* disabled when p == current.
*
* The rules of saved_state:
*
* The related locking code always holds p::pi_lock when updating
* p::saved_state, which means the code is fully serialized in both cases.
*
* For PREEMPT_RT, the lock wait and lock wakeups happen via TASK_RTLOCK_WAIT.
* No other bits set. This allows to distinguish all wakeup scenarios.
*
* For FREEZER, the wakeup happens via TASK_FROZEN. No other bits set. This
* allows us to prevent early wakeup of tasks before they can be run on
* asymmetric ISA architectures (eg ARMv9).
*/
static __always_inline
bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
{
int match;
if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) {
WARN_ON_ONCE((state & TASK_RTLOCK_WAIT) &&
state != TASK_RTLOCK_WAIT);
}
*success = !!(match = __task_state_match(p, state));
/*
* Saved state preserves the task state across blocking on
* an RT lock or TASK_FREEZABLE tasks. If the state matches,
* set p::saved_state to TASK_RUNNING, but do not wake the task
* because it waits for a lock wakeup or __thaw_task(). Also
* indicate success because from the regular waker's point of
* view this has succeeded.
*
* After acquiring the lock the task will restore p::__state
* from p::saved_state which ensures that the regular
* wakeup is not lost. The restore will also set
* p::saved_state to TASK_RUNNING so any further tests will
* not result in false positives vs. @success
*/
if (match < 0)
p->saved_state = TASK_RUNNING;
return match > 0;
}
/*
* Notes on Program-Order guarantees on SMP systems.
*
* MIGRATION
*
* The basic program-order guarantee on SMP systems is that when a task [t]
* migrates, all its activity on its old CPU [c0] happens-before any subsequent
* execution on its new CPU [c1].
*
* For migration (of runnable tasks) this is provided by the following means:
*
* A) UNLOCK of the rq(c0)->lock scheduling out task t
* B) migration for t is required to synchronize *both* rq(c0)->lock and
* rq(c1)->lock (if not at the same time, then in that order).
* C) LOCK of the rq(c1)->lock scheduling in task
*
* Release/acquire chaining guarantees that B happens after A and C after B.
* Note: the CPU doing B need not be c0 or c1
*
* Example:
*
* CPU0 CPU1 CPU2
*
* LOCK rq(0)->lock
* sched-out X
* sched-in Y
* UNLOCK rq(0)->lock
*
* LOCK rq(0)->lock // orders against CPU0
* dequeue X
* UNLOCK rq(0)->lock
*
* LOCK rq(1)->lock
* enqueue X
* UNLOCK rq(1)->lock
*
* LOCK rq(1)->lock // orders against CPU2
* sched-out Z
* sched-in X
* UNLOCK rq(1)->lock
*
*
* BLOCKING -- aka. SLEEP + WAKEUP
*
* For blocking we (obviously) need to provide the same guarantee as for
* migration. However the means are completely different as there is no lock
* chain to provide order. Instead we do:
*
* 1) smp_store_release(X->on_cpu, 0) -- finish_task()
* 2) smp_cond_load_acquire(!X->on_cpu) -- try_to_wake_up()
*
* Example:
*
* CPU0 (schedule) CPU1 (try_to_wake_up) CPU2 (schedule)
*
* LOCK rq(0)->lock LOCK X->pi_lock
* dequeue X
* sched-out X
* smp_store_release(X->on_cpu, 0);
*
* smp_cond_load_acquire(&X->on_cpu, !VAL);
* X->state = WAKING
* set_task_cpu(X,2)
*
* LOCK rq(2)->lock
* enqueue X
* X->state = RUNNING
* UNLOCK rq(2)->lock
*
* LOCK rq(2)->lock // orders against CPU1
* sched-out Z
* sched-in X
* UNLOCK rq(2)->lock
*
* UNLOCK X->pi_lock
* UNLOCK rq(0)->lock
*
*
* However, for wakeups there is a second guarantee we must provide, namely we
* must ensure that CONDITION=1 done by the caller can not be reordered with
* accesses to the task state; see try_to_wake_up() and set_current_state().
*/
/**
* try_to_wake_up - wake up a thread
* @p: the thread to be awakened
* @state: the mask of task states that can be woken
* @wake_flags: wake modifier flags (WF_*)
*
* Conceptually does:
*
* If (@state & @p->state) @p->state = TASK_RUNNING.
*
* If the task was not queued/runnable, also place it back on a runqueue.
*
* This function is atomic against schedule() which would dequeue the task.
*
* It issues a full memory barrier before accessing @p->state, see the comment
* with set_current_state().
*
* Uses p->pi_lock to serialize against concurrent wake-ups.
*
* Relies on p->pi_lock stabilizing:
* - p->sched_class
* - p->cpus_ptr
* - p->sched_task_group
* in order to do migration, see its use of select_task_rq()/set_task_cpu().
*
* Tries really hard to only take one task_rq(p)->lock for performance.
* Takes rq->lock in:
* - ttwu_runnable() -- old rq, unavoidable, see comment there;
* - ttwu_queue() -- new rq, for enqueue of the task;
* - psi_ttwu_dequeue() -- much sadness :-( accounting will kill us.
*
* As a consequence we race really badly with just about everything. See the
* many memory barriers and their comments for details.
*
* Return: %true if @p->state changes (an actual wakeup was done),
* %false otherwise.
*/
int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
{
guard(preempt)();
int cpu, success = 0;
if (p == current) {
/*
* We're waking current, this means 'p->on_rq' and 'task_cpu(p)
* == smp_processor_id()'. Together this means we can special
* case the whole 'p->on_rq && ttwu_runnable()' case below
* without taking any locks.
*
* Specifically, given current runs ttwu() we must be before
* schedule()'s block_task(), as such this must not observe
* sched_delayed.
*
* In particular:
* - we rely on Program-Order guarantees for all the ordering,
* - we're serialized against set_special_state() by virtue of
* it disabling IRQs (this allows not taking ->pi_lock).
*/
SCHED_WARN_ON(p->se.sched_delayed);
if (!ttwu_state_match(p, state, &success))
goto out;
trace_sched_waking(p);
ttwu_do_wakeup(p);
goto out;
}
/*
* If we are going to wake up a thread waiting for CONDITION we
* need to ensure that CONDITION=1 done by the caller can not be
* reordered with p->state check below. This pairs with smp_store_mb()
* in set_current_state() that the waiting thread does.
*/
scoped_guard (raw_spinlock_irqsave, &p->pi_lock) {
smp_mb__after_spinlock();
if (!ttwu_state_match(p, state, &success))
break;
trace_sched_waking(p);
/*
* Ensure we load p->on_rq _after_ p->state, otherwise it would
* be possible to, falsely, observe p->on_rq == 0 and get stuck
* in smp_cond_load_acquire() below.
*
* sched_ttwu_pending() try_to_wake_up()
* STORE p->on_rq = 1 LOAD p->state
* UNLOCK rq->lock
*
* __schedule() (switch to task 'p')
* LOCK rq->lock smp_rmb();
* smp_mb__after_spinlock();
* UNLOCK rq->lock
*
* [task p]
* STORE p->state = UNINTERRUPTIBLE LOAD p->on_rq
*
* Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
* __schedule(). See the comment for smp_mb__after_spinlock().
*
* A similar smp_rmb() lives in __task_needs_rq_lock().
*/
smp_rmb();
if (READ_ONCE(p->on_rq) && ttwu_runnable(p, wake_flags))
break;
#ifdef CONFIG_SMP
/*
* Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
* possible to, falsely, observe p->on_cpu == 0.
*
* One must be running (->on_cpu == 1) in order to remove oneself
* from the runqueue.
*
* __schedule() (switch to task 'p') try_to_wake_up()
* STORE p->on_cpu = 1 LOAD p->on_rq
* UNLOCK rq->lock
*
* __schedule() (put 'p' to sleep)
* LOCK rq->lock smp_rmb();
* smp_mb__after_spinlock();
* STORE p->on_rq = 0 LOAD p->on_cpu
*
* Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
* __schedule(). See the comment for smp_mb__after_spinlock().
*
* Form a control-dep-acquire with p->on_rq == 0 above, to ensure
* schedule()'s deactivate_task() has 'happened' and p will no longer
* care about it's own p->state. See the comment in __schedule().
*/
smp_acquire__after_ctrl_dep();
/*
* We're doing the wakeup (@success == 1), they did a dequeue (p->on_rq
* == 0), which means we need to do an enqueue, change p->state to
* TASK_WAKING such that we can unlock p->pi_lock before doing the
* enqueue, such as ttwu_queue_wakelist().
*/
WRITE_ONCE(p->__state, TASK_WAKING);
/*
* If the owning (remote) CPU is still in the middle of schedule() with
* this task as prev, considering queueing p on the remote CPUs wake_list
* which potentially sends an IPI instead of spinning on p->on_cpu to
* let the waker make forward progress. This is safe because IRQs are
* disabled and the IPI will deliver after on_cpu is cleared.
*
* Ensure we load task_cpu(p) after p->on_cpu:
*
* set_task_cpu(p, cpu);
* STORE p->cpu = @cpu
* __schedule() (switch to task 'p')
* LOCK rq->lock
* smp_mb__after_spin_lock() smp_cond_load_acquire(&p->on_cpu)
* STORE p->on_cpu = 1 LOAD p->cpu
*
* to ensure we observe the correct CPU on which the task is currently
* scheduling.
*/
if (smp_load_acquire(&p->on_cpu) &&
ttwu_queue_wakelist(p, task_cpu(p), wake_flags))
break;
/*
* If the owning (remote) CPU is still in the middle of schedule() with
* this task as prev, wait until it's done referencing the task.
*
* Pairs with the smp_store_release() in finish_task().
*
* This ensures that tasks getting woken will be fully ordered against
* their previous state and preserve Program Order.
*/
smp_cond_load_acquire(&p->on_cpu, !VAL);
cpu = select_task_rq(p, p->wake_cpu, wake_flags | WF_TTWU);
if (task_cpu(p) != cpu) {
if (p->in_iowait) {
delayacct_blkio_end(p);
atomic_dec(&task_rq(p)->nr_iowait);
}
wake_flags |= WF_MIGRATED;
psi_ttwu_dequeue(p);
set_task_cpu(p, cpu);
}
#else
cpu = task_cpu(p);
#endif /* CONFIG_SMP */
ttwu_queue(p, cpu, wake_flags);
}
out:
if (success)
ttwu_stat(p, task_cpu(p), wake_flags);
return success;
}
static bool __task_needs_rq_lock(struct task_struct *p)
{
unsigned int state = READ_ONCE(p->__state);
/*
* Since pi->lock blocks try_to_wake_up(), we don't need rq->lock when
* the task is blocked. Make sure to check @state since ttwu() can drop
* locks at the end, see ttwu_queue_wakelist().
*/
if (state == TASK_RUNNING || state == TASK_WAKING)
return true;
/*
* Ensure we load p->on_rq after p->__state, otherwise it would be
* possible to, falsely, observe p->on_rq == 0.
*
* See try_to_wake_up() for a longer comment.
*/
smp_rmb();
if (p->on_rq)
return true;
#ifdef CONFIG_SMP
/*
* Ensure the task has finished __schedule() and will not be referenced
* anymore. Again, see try_to_wake_up() for a longer comment.
*/
smp_rmb();
smp_cond_load_acquire(&p->on_cpu, !VAL);
#endif
return false;
}
/**
* task_call_func - Invoke a function on task in fixed state
* @p: Process for which the function is to be invoked, can be @current.
* @func: Function to invoke.
* @arg: Argument to function.
*
* Fix the task in it's current state by avoiding wakeups and or rq operations
* and call @func(@arg) on it. This function can use ->on_rq and task_curr()
* to work out what the state is, if required. Given that @func can be invoked
* with a runqueue lock held, it had better be quite lightweight.
*
* Returns:
* Whatever @func returns
*/
int task_call_func(struct task_struct *p, task_call_f func, void *arg)
{
struct rq *rq = NULL;
struct rq_flags rf;
int ret;
raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
if (__task_needs_rq_lock(p))
rq = __task_rq_lock(p, &rf);
/*
* At this point the task is pinned; either:
* - blocked and we're holding off wakeups (pi->lock)
* - woken, and we're holding off enqueue (rq->lock)
* - queued, and we're holding off schedule (rq->lock)
* - running, and we're holding off de-schedule (rq->lock)
*
* The called function (@func) can use: task_curr(), p->on_rq and
* p->__state to differentiate between these states.
*/
ret = func(p, arg);
if (rq)
rq_unlock(rq, &rf);
raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
return ret;
}
/**
* cpu_curr_snapshot - Return a snapshot of the currently running task
* @cpu: The CPU on which to snapshot the task.
*
* Returns the task_struct pointer of the task "currently" running on
* the specified CPU.
*
* If the specified CPU was offline, the return value is whatever it
* is, perhaps a pointer to the task_struct structure of that CPU's idle
* task, but there is no guarantee. Callers wishing a useful return
* value must take some action to ensure that the specified CPU remains
* online throughout.
*
* This function executes full memory barriers before and after fetching
* the pointer, which permits the caller to confine this function's fetch
* with respect to the caller's accesses to other shared variables.
*/
struct task_struct *cpu_curr_snapshot(int cpu)
{
struct rq *rq = cpu_rq(cpu);
struct task_struct *t;
struct rq_flags rf;
rq_lock_irqsave(rq, &rf);
smp_mb__after_spinlock(); /* Pairing determined by caller's synchronization design. */
t = rcu_dereference(cpu_curr(cpu));
rq_unlock_irqrestore(rq, &rf);
smp_mb(); /* Pairing determined by caller's synchronization design. */
return t;
}
/**
* wake_up_process - Wake up a specific process
* @p: The process to be woken up.
*
* Attempt to wake up the nominated process and move it to the set of runnable
* processes.
*
* Return: 1 if the process was woken up, 0 if it was already running.
*
* This function executes a full memory barrier before accessing the task state.
*/
int wake_up_process(struct task_struct *p)
{
return try_to_wake_up(p, TASK_NORMAL, 0);
}
EXPORT_SYMBOL(wake_up_process);
int wake_up_state(struct task_struct *p, unsigned int state)
{
return try_to_wake_up(p, state, 0);
}
/*
* Perform scheduler related setup for a newly forked process p.
* p is forked by current.
*
* __sched_fork() is basic setup used by init_idle() too:
*/
static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
{
p->on_rq = 0;
p->se.on_rq = 0;
p->se.exec_start = 0;
p->se.sum_exec_runtime = 0;
p->se.prev_sum_exec_runtime = 0;
p->se.nr_migrations = 0;
p->se.vruntime = 0;
p->se.vlag = 0;
INIT_LIST_HEAD(&p->se.group_node);
/* A delayed task cannot be in clone(). */
SCHED_WARN_ON(p->se.sched_delayed);
#ifdef CONFIG_FAIR_GROUP_SCHED
p->se.cfs_rq = NULL;
#endif
#ifdef CONFIG_SCHEDSTATS
/* Even if schedstat is disabled, there should not be garbage */
memset(&p->stats, 0, sizeof(p->stats));
#endif
init_dl_entity(&p->dl);
INIT_LIST_HEAD(&p->rt.run_list);
p->rt.timeout = 0;
p->rt.time_slice = sched_rr_timeslice;
p->rt.on_rq = 0;
p->rt.on_list = 0;
#ifdef CONFIG_SCHED_CLASS_EXT
init_scx_entity(&p->scx);
#endif
#ifdef CONFIG_PREEMPT_NOTIFIERS
INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif
#ifdef CONFIG_COMPACTION
p->capture_control = NULL;
#endif
init_numa_balancing(clone_flags, p);
#ifdef CONFIG_SMP
p->wake_entry.u_flags = CSD_TYPE_TTWU;
p->migration_pending = NULL;
#endif
init_sched_mm_cid(p);
}
DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
#ifdef CONFIG_NUMA_BALANCING
int sysctl_numa_balancing_mode;
static void __set_numabalancing_state(bool enabled)
{
if (enabled)
static_branch_enable(&sched_numa_balancing);
else
static_branch_disable(&sched_numa_balancing);
}
void set_numabalancing_state(bool enabled)
{
if (enabled)
sysctl_numa_balancing_mode = NUMA_BALANCING_NORMAL;
else
sysctl_numa_balancing_mode = NUMA_BALANCING_DISABLED;
__set_numabalancing_state(enabled);
}
#ifdef CONFIG_PROC_SYSCTL
static void reset_memory_tiering(void)
{
struct pglist_data *pgdat;
for_each_online_pgdat(pgdat) {
pgdat->nbp_threshold = 0;
pgdat->nbp_th_nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
pgdat->nbp_th_start = jiffies_to_msecs(jiffies);
}
}
static int sysctl_numa_balancing(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
struct ctl_table t;
int err;
int state = sysctl_numa_balancing_mode;
if (write && !capable(CAP_SYS_ADMIN))
return -EPERM;
t = *table;
t.data = &state;
err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
if (err < 0)
return err;
if (write) {
if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
(state & NUMA_BALANCING_MEMORY_TIERING))
reset_memory_tiering();
sysctl_numa_balancing_mode = state;
__set_numabalancing_state(state);
}
return err;
}
#endif
#endif
#ifdef CONFIG_SCHEDSTATS
DEFINE_STATIC_KEY_FALSE(sched_schedstats);
static void set_schedstats(bool enabled)
{
if (enabled)
static_branch_enable(&sched_schedstats);
else
static_branch_disable(&sched_schedstats);
}
void force_schedstat_enabled(void)
{
if (!schedstat_enabled()) {
pr_info("kernel profiling enabled schedstats, disable via kernel.sched_schedstats.\n");
static_branch_enable(&sched_schedstats);
}
}
static int __init setup_schedstats(char *str)
{
int ret = 0;
if (!str)
goto out;
if (!strcmp(str, "enable")) {
set_schedstats(true);
ret = 1;
} else if (!strcmp(str, "disable")) {
set_schedstats(false);
ret = 1;
}
out:
if (!ret)
pr_warn("Unable to parse schedstats=\n");
return ret;
}
__setup("schedstats=", setup_schedstats);
#ifdef CONFIG_PROC_SYSCTL
static int sysctl_schedstats(const struct ctl_table *table, int write, void *buffer,
size_t *lenp, loff_t *ppos)
{
struct ctl_table t;
int err;
int state = static_branch_likely(&sched_schedstats);
if (write && !capable(CAP_SYS_ADMIN))
return -EPERM;
t = *table;
t.data = &state;
err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
if (err < 0)
return err;
if (write)
set_schedstats(state);
return err;
}
#endif /* CONFIG_PROC_SYSCTL */
#endif /* CONFIG_SCHEDSTATS */
#ifdef CONFIG_SYSCTL
static struct ctl_table sched_core_sysctls[] = {
#ifdef CONFIG_SCHEDSTATS
{
.procname = "sched_schedstats",
.data = NULL,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = sysctl_schedstats,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
#endif /* CONFIG_SCHEDSTATS */
#ifdef CONFIG_UCLAMP_TASK
{
.procname = "sched_util_clamp_min",
.data = &sysctl_sched_uclamp_util_min,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = sysctl_sched_uclamp_handler,
},
{
.procname = "sched_util_clamp_max",
.data = &sysctl_sched_uclamp_util_max,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = sysctl_sched_uclamp_handler,
},
{
.procname = "sched_util_clamp_min_rt_default",
.data = &sysctl_sched_uclamp_util_min_rt_default,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = sysctl_sched_uclamp_handler,
},
#endif /* CONFIG_UCLAMP_TASK */
#ifdef CONFIG_NUMA_BALANCING
{
.procname = "numa_balancing",
.data = NULL, /* filled in by handler */
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = sysctl_numa_balancing,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_FOUR,
},
#endif /* CONFIG_NUMA_BALANCING */
};
static int __init sched_core_sysctl_init(void)
{
register_sysctl_init("kernel", sched_core_sysctls);
return 0;
}
late_initcall(sched_core_sysctl_init);
#endif /* CONFIG_SYSCTL */
/*
* fork()/clone()-time setup:
*/
int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
__sched_fork(clone_flags, p);
/*
* We mark the process as NEW here. This guarantees that
* nobody will actually run it, and a signal or other external
* event cannot wake it up and insert it on the runqueue either.
*/
p->__state = TASK_NEW;
/*
* Make sure we do not leak PI boosting priority to the child.
*/
p->prio = current->normal_prio;
uclamp_fork(p);
/*
* Revert to default priority/policy on fork if requested.
*/
if (unlikely(p->sched_reset_on_fork)) {
if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
p->policy = SCHED_NORMAL;
p->static_prio = NICE_TO_PRIO(0);
p->rt_priority = 0;
} else if (PRIO_TO_NICE(p->static_prio) < 0)
p->static_prio = NICE_TO_PRIO(0);
p->prio = p->normal_prio = p->static_prio;
set_load_weight(p, false);
p->se.custom_slice = 0;
p->se.slice = sysctl_sched_base_slice;
/*
* We don't need the reset flag anymore after the fork. It has
* fulfilled its duty:
*/
p->sched_reset_on_fork = 0;
}
if (dl_prio(p->prio))
return -EAGAIN;
scx_pre_fork(p);
if (rt_prio(p->prio)) {
p->sched_class = &rt_sched_class;
#ifdef CONFIG_SCHED_CLASS_EXT
} else if (task_should_scx(p)) {
p->sched_class = &ext_sched_class;
#endif
} else {
p->sched_class = &fair_sched_class;
}
init_entity_runnable_average(&p->se);
#ifdef CONFIG_SCHED_INFO
if (likely(sched_info_on()))
memset(&p->sched_info, 0, sizeof(p->sched_info));
#endif
#if defined(CONFIG_SMP)
p->on_cpu = 0;
#endif
init_task_preempt_count(p);
#ifdef CONFIG_SMP
plist_node_init(&p->pushable_tasks, MAX_PRIO);
RB_CLEAR_NODE(&p->pushable_dl_tasks);
#endif
return 0;
}
int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
{
unsigned long flags;
/*
* Because we're not yet on the pid-hash, p->pi_lock isn't strictly
* required yet, but lockdep gets upset if rules are violated.
*/
raw_spin_lock_irqsave(&p->pi_lock, flags);
#ifdef CONFIG_CGROUP_SCHED
if (1) {
struct task_group *tg;
tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
struct task_group, css);
tg = autogroup_task_group(p, tg);
p->sched_task_group = tg;
}
#endif
rseq_migrate(p);
/*
* We're setting the CPU for the first time, we don't migrate,
* so use __set_task_cpu().
*/
__set_task_cpu(p, smp_processor_id());
if (p->sched_class->task_fork)
p->sched_class->task_fork(p);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
return scx_fork(p);
}
void sched_cancel_fork(struct task_struct *p)
{
scx_cancel_fork(p);
}
void sched_post_fork(struct task_struct *p)
{
uclamp_post_fork(p);
scx_post_fork(p);
}
unsigned long to_ratio(u64 period, u64 runtime)
{
if (runtime == RUNTIME_INF)
return BW_UNIT;
/*
* Doing this here saves a lot of checks in all
* the calling paths, and returning zero seems
* safe for them anyway.
*/
if (period == 0)
return 0;
return div64_u64(runtime << BW_SHIFT, period);
}
/*
* wake_up_new_task - wake up a newly created task for the first time.
*
* This function will do some initial scheduler statistics housekeeping
* that must be done for every newly created context, then puts the task
* on the runqueue and wakes it.
*/
void wake_up_new_task(struct task_struct *p)
{
struct rq_flags rf;
struct rq *rq;
raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
WRITE_ONCE(p->__state, TASK_RUNNING);
#ifdef CONFIG_SMP
/*
* Fork balancing, do it here and not earlier because:
* - cpus_ptr can change in the fork path
* - any previously selected CPU might disappear through hotplug
*
* Use __set_task_cpu() to avoid calling sched_class::migrate_task_rq,
* as we're not fully set-up yet.
*/
p->recent_used_cpu = task_cpu(p);
rseq_migrate(p);
__set_task_cpu(p, select_task_rq(p, task_cpu(p), WF_FORK));
#endif
rq = __task_rq_lock(p, &rf);
update_rq_clock(rq);
post_init_entity_util_avg(p);
activate_task(rq, p, ENQUEUE_NOCLOCK | ENQUEUE_INITIAL);
trace_sched_wakeup_new(p);
wakeup_preempt(rq, p, WF_FORK);
#ifdef CONFIG_SMP
if (p->sched_class->task_woken) {
/*
* Nothing relies on rq->lock after this, so it's fine to
* drop it.
*/
rq_unpin_lock(rq, &rf);
p->sched_class->task_woken(rq, p);
rq_repin_lock(rq, &rf);
}
#endif
task_rq_unlock(rq, p, &rf);
}
#ifdef CONFIG_PREEMPT_NOTIFIERS
static DEFINE_STATIC_KEY_FALSE(preempt_notifier_key);
void preempt_notifier_inc(void)
{
static_branch_inc(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_inc);
void preempt_notifier_dec(void)
{
static_branch_dec(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_dec);
/**
* preempt_notifier_register - tell me when current is being preempted & rescheduled
* @notifier: notifier struct to register
*/
void preempt_notifier_register(struct preempt_notifier *notifier)
{
if (!static_branch_unlikely(&preempt_notifier_key))
WARN(1, "registering preempt_notifier while notifiers disabled\n");
hlist_add_head(¬ifier->link, ¤t->preempt_notifiers);
}
EXPORT_SYMBOL_GPL(preempt_notifier_register);
/**
* preempt_notifier_unregister - no longer interested in preemption notifications
* @notifier: notifier struct to unregister
*
* This is *not* safe to call from within a preemption notifier.
*/
void preempt_notifier_unregister(struct preempt_notifier *notifier)
{
hlist_del(¬ifier->link);
}
EXPORT_SYMBOL_GPL(preempt_notifier_unregister);
static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
struct preempt_notifier *notifier;
hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
notifier->ops->sched_in(notifier, raw_smp_processor_id());
}
static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
if (static_branch_unlikely(&preempt_notifier_key))
__fire_sched_in_preempt_notifiers(curr);
}
static void
__fire_sched_out_preempt_notifiers(struct task_struct *curr,
struct task_struct *next)
{
struct preempt_notifier *notifier;
hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
notifier->ops->sched_out(notifier, next);
}
static __always_inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
struct task_struct *next)
{
if (static_branch_unlikely(&preempt_notifier_key))
__fire_sched_out_preempt_notifiers(curr, next);
}
#else /* !CONFIG_PREEMPT_NOTIFIERS */
static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
}
static inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
struct task_struct *next)
{
}
#endif /* CONFIG_PREEMPT_NOTIFIERS */
static inline void prepare_task(struct task_struct *next)
{
#ifdef CONFIG_SMP
/*
* Claim the task as running, we do this before switching to it
* such that any running task will have this set.
*
* See the smp_load_acquire(&p->on_cpu) case in ttwu() and
* its ordering comment.
*/
WRITE_ONCE(next->on_cpu, 1);
#endif
}
static inline void finish_task(struct task_struct *prev)
{
#ifdef CONFIG_SMP
/*
* This must be the very last reference to @prev from this CPU. After
* p->on_cpu is cleared, the task can be moved to a different CPU. We
* must ensure this doesn't happen until the switch is completely
* finished.
*
* In particular, the load of prev->state in finish_task_switch() must
* happen before this.
*
* Pairs with the smp_cond_load_acquire() in try_to_wake_up().
*/
smp_store_release(&prev->on_cpu, 0);
#endif
}
#ifdef CONFIG_SMP
static void do_balance_callbacks(struct rq *rq, struct balance_callback *head)
{
void (*func)(struct rq *rq);
struct balance_callback *next;
lockdep_assert_rq_held(rq);
while (head) {
func = (void (*)(struct rq *))head->func;
next = head->next;
head->next = NULL;
head = next;
func(rq);
}
}
static void balance_push(struct rq *rq);
/*
* balance_push_callback is a right abuse of the callback interface and plays
* by significantly different rules.
*
* Where the normal balance_callback's purpose is to be ran in the same context
* that queued it (only later, when it's safe to drop rq->lock again),
* balance_push_callback is specifically targeted at __schedule().
*
* This abuse is tolerated because it places all the unlikely/odd cases behind
* a single test, namely: rq->balance_callback == NULL.
*/
struct balance_callback balance_push_callback = {
.next = NULL,
.func = balance_push,
};
static inline struct balance_callback *
__splice_balance_callbacks(struct rq *rq, bool split)
{
struct balance_callback *head = rq->balance_callback;
if (likely(!head))
return NULL;
lockdep_assert_rq_held(rq);
/*
* Must not take balance_push_callback off the list when
* splice_balance_callbacks() and balance_callbacks() are not
* in the same rq->lock section.
*
* In that case it would be possible for __schedule() to interleave
* and observe the list empty.
*/
if (split && head == &balance_push_callback)
head = NULL;
else
rq->balance_callback = NULL;
return head;
}
struct balance_callback *splice_balance_callbacks(struct rq *rq)
{
return __splice_balance_callbacks(rq, true);
}
static void __balance_callbacks(struct rq *rq)
{
do_balance_callbacks(rq, __splice_balance_callbacks(rq, false));
}
void balance_callbacks(struct rq *rq, struct balance_callback *head)
{
unsigned long flags;
if (unlikely(head)) {
raw_spin_rq_lock_irqsave(rq, flags);
do_balance_callbacks(rq, head);
raw_spin_rq_unlock_irqrestore(rq, flags);
}
}
#else
static inline void __balance_callbacks(struct rq *rq)
{
}
#endif
static inline void
prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
{
/*
* Since the runqueue lock will be released by the next
* task (which is an invalid locking op but in the case
* of the scheduler it's an obvious special-case), so we
* do an early lockdep release here:
*/
rq_unpin_lock(rq, rf);
spin_release(&__rq_lockp(rq)->dep_map, _THIS_IP_);
#ifdef CONFIG_DEBUG_SPINLOCK
/* this is a valid case when another task releases the spinlock */
rq_lockp(rq)->owner = next;
#endif
}
static inline void finish_lock_switch(struct rq *rq)
{
/*
* If we are tracking spinlock dependencies then we have to
* fix up the runqueue lock - which gets 'carried over' from
* prev into current:
*/
spin_acquire(&__rq_lockp(rq)->dep_map, 0, 0, _THIS_IP_);
__balance_callbacks(rq);
raw_spin_rq_unlock_irq(rq);
}
/*
* NOP if the arch has not defined these:
*/
#ifndef prepare_arch_switch
# define prepare_arch_switch(next) do { } while (0)
#endif
#ifndef finish_arch_post_lock_switch
# define finish_arch_post_lock_switch() do { } while (0)
#endif
static inline void kmap_local_sched_out(void)
{
#ifdef CONFIG_KMAP_LOCAL
if (unlikely(current->kmap_ctrl.idx))
__kmap_local_sched_out();
#endif
}
static inline void kmap_local_sched_in(void)
{
#ifdef CONFIG_KMAP_LOCAL
if (unlikely(current->kmap_ctrl.idx))
__kmap_local_sched_in();
#endif
}
/**
* prepare_task_switch - prepare to switch tasks
* @rq: the runqueue preparing to switch
* @prev: the current task that is being switched out
* @next: the task we are going to switch to.
*
* This is called with the rq lock held and interrupts off. It must
* be paired with a subsequent finish_task_switch after the context
* switch.
*
* prepare_task_switch sets up locking and calls architecture specific
* hooks.
*/
static inline void
prepare_task_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next)
{
kcov_prepare_switch(prev);
sched_info_switch(rq, prev, next);
perf_event_task_sched_out(prev, next);
rseq_preempt(prev);
fire_sched_out_preempt_notifiers(prev, next);
kmap_local_sched_out();
prepare_task(next);
prepare_arch_switch(next);
}
/**
* finish_task_switch - clean up after a task-switch
* @prev: the thread we just switched away from.
*
* finish_task_switch must be called after the context switch, paired
* with a prepare_task_switch call before the context switch.
* finish_task_switch will reconcile locking set up by prepare_task_switch,
* and do any other architecture-specific cleanup actions.
*
* Note that we may have delayed dropping an mm in context_switch(). If
* so, we finish that here outside of the runqueue lock. (Doing it
* with the lock held can cause deadlocks; see schedule() for
* details.)
*
* The context switch have flipped the stack from under us and restored the
* local variables which were saved when this task called schedule() in the
* past. 'prev == current' is still correct but we need to recalculate this_rq
* because prev may have moved to another CPU.
*/
static struct rq *finish_task_switch(struct task_struct *prev)
__releases(rq->lock)
{
struct rq *rq = this_rq();
struct mm_struct *mm = rq->prev_mm;
unsigned int prev_state;
/*
* The previous task will have left us with a preempt_count of 2
* because it left us after:
*
* schedule()
* preempt_disable(); // 1
* __schedule()
* raw_spin_lock_irq(&rq->lock) // 2
*
* Also, see FORK_PREEMPT_COUNT.
*/
if (WARN_ONCE(preempt_count() != 2*PREEMPT_DISABLE_OFFSET,
"corrupted preempt_count: %s/%d/0x%x\n",
current->comm, current->pid, preempt_count()))
preempt_count_set(FORK_PREEMPT_COUNT);
rq->prev_mm = NULL;
/*
* A task struct has one reference for the use as "current".
* If a task dies, then it sets TASK_DEAD in tsk->state and calls
* schedule one last time. The schedule call will never return, and
* the scheduled task must drop that reference.
*
* We must observe prev->state before clearing prev->on_cpu (in
* finish_task), otherwise a concurrent wakeup can get prev
* running on another CPU and we could rave with its RUNNING -> DEAD
* transition, resulting in a double drop.
*/
prev_state = READ_ONCE(prev->__state);
vtime_task_switch(prev);
perf_event_task_sched_in(prev, current);
finish_task(prev);
tick_nohz_task_switch();
finish_lock_switch(rq);
finish_arch_post_lock_switch();
kcov_finish_switch(current);
/*
* kmap_local_sched_out() is invoked with rq::lock held and
* interrupts disabled. There is no requirement for that, but the
* sched out code does not have an interrupt enabled section.
* Restoring the maps on sched in does not require interrupts being
* disabled either.
*/
kmap_local_sched_in();
fire_sched_in_preempt_notifiers(current);
/*
* When switching through a kernel thread, the loop in
* membarrier_{private,global}_expedited() may have observed that
* kernel thread and not issued an IPI. It is therefore possible to
* schedule between user->kernel->user threads without passing though
* switch_mm(). Membarrier requires a barrier after storing to
* rq->curr, before returning to userspace, so provide them here:
*
* - a full memory barrier for {PRIVATE,GLOBAL}_EXPEDITED, implicitly
* provided by mmdrop_lazy_tlb(),
* - a sync_core for SYNC_CORE.
*/
if (mm) {
membarrier_mm_sync_core_before_usermode(mm);
mmdrop_lazy_tlb_sched(mm);
}
if (unlikely(prev_state == TASK_DEAD)) {
if (prev->sched_class->task_dead)
prev->sched_class->task_dead(prev);
/* Task is done with its stack. */
put_task_stack(prev);
put_task_struct_rcu_user(prev);
}
return rq;
}
/**
* schedule_tail - first thing a freshly forked thread must call.
* @prev: the thread we just switched away from.
*/
asmlinkage __visible void schedule_tail(struct task_struct *prev)
__releases(rq->lock)
{
/*
* New tasks start with FORK_PREEMPT_COUNT, see there and
* finish_task_switch() for details.
*
* finish_task_switch() will drop rq->lock() and lower preempt_count
* and the preempt_enable() will end up enabling preemption (on
* PREEMPT_COUNT kernels).
*/
finish_task_switch(prev);
preempt_enable();
if (current->set_child_tid)
put_user(task_pid_vnr(current), current->set_child_tid);
calculate_sigpending();
}
/*
* context_switch - switch to the new MM and the new thread's register state.
*/
static __always_inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next, struct rq_flags *rf)
{
prepare_task_switch(rq, prev, next);
/*
* For paravirt, this is coupled with an exit in switch_to to
* combine the page table reload and the switch backend into
* one hypercall.
*/
arch_start_context_switch(prev);
/*
* kernel -> kernel lazy + transfer active
* user -> kernel lazy + mmgrab_lazy_tlb() active
*
* kernel -> user switch + mmdrop_lazy_tlb() active
* user -> user switch
*
* switch_mm_cid() needs to be updated if the barriers provided
* by context_switch() are modified.
*/
if (!next->mm) { // to kernel
enter_lazy_tlb(prev->active_mm, next);
next->active_mm = prev->active_mm;
if (prev->mm) // from user
mmgrab_lazy_tlb(prev->active_mm);
else
prev->active_mm = NULL;
} else { // to user
membarrier_switch_mm(rq, prev->active_mm, next->mm);
/*
* sys_membarrier() requires an smp_mb() between setting
* rq->curr / membarrier_switch_mm() and returning to userspace.
*
* The below provides this either through switch_mm(), or in
* case 'prev->active_mm == next->mm' through
* finish_task_switch()'s mmdrop().
*/
switch_mm_irqs_off(prev->active_mm, next->mm, next);
lru_gen_use_mm(next->mm);
if (!prev->mm) { // from kernel
/* will mmdrop_lazy_tlb() in finish_task_switch(). */
rq->prev_mm = prev->active_mm;
prev->active_mm = NULL;
}
}
/* switch_mm_cid() requires the memory barriers above. */
switch_mm_cid(rq, prev, next);
prepare_lock_switch(rq, next, rf);
/* Here we just switch the register state and the stack. */
switch_to(prev, next, prev);
barrier();
return finish_task_switch(prev);
}
/*
* nr_running and nr_context_switches:
*
* externally visible scheduler statistics: current number of runnable
* threads, total number of context switches performed since bootup.
*/
unsigned int nr_running(void)
{
unsigned int i, sum = 0;
for_each_online_cpu(i)
sum += cpu_rq(i)->nr_running;
return sum;
}
/*
* Check if only the current task is running on the CPU.
*
* Caution: this function does not check that the caller has disabled
* preemption, thus the result might have a time-of-check-to-time-of-use
* race. The caller is responsible to use it correctly, for example:
*
* - from a non-preemptible section (of course)
*
* - from a thread that is bound to a single CPU
*
* - in a loop with very short iterations (e.g. a polling loop)
*/
bool single_task_running(void)
{
return raw_rq()->nr_running == 1;
}
EXPORT_SYMBOL(single_task_running);
unsigned long long nr_context_switches_cpu(int cpu)
{
return cpu_rq(cpu)->nr_switches;
}
unsigned long long nr_context_switches(void)
{
int i;
unsigned long long sum = 0;
for_each_possible_cpu(i)
sum += cpu_rq(i)->nr_switches;
return sum;
}
/*
* Consumers of these two interfaces, like for example the cpuidle menu
* governor, are using nonsensical data. Preferring shallow idle state selection
* for a CPU that has IO-wait which might not even end up running the task when
* it does become runnable.
*/
unsigned int nr_iowait_cpu(int cpu)
{
return atomic_read(&cpu_rq(cpu)->nr_iowait);
}
/*
* IO-wait accounting, and how it's mostly bollocks (on SMP).
*
* The idea behind IO-wait account is to account the idle time that we could
* have spend running if it were not for IO. That is, if we were to improve the
* storage performance, we'd have a proportional reduction in IO-wait time.
*
* This all works nicely on UP, where, when a task blocks on IO, we account
* idle time as IO-wait, because if the storage were faster, it could've been
* running and we'd not be idle.
*
* This has been extended to SMP, by doing the same for each CPU. This however
* is broken.
*
* Imagine for instance the case where two tasks block on one CPU, only the one
* CPU will have IO-wait accounted, while the other has regular idle. Even
* though, if the storage were faster, both could've ran at the same time,
* utilising both CPUs.
*
* This means, that when looking globally, the current IO-wait accounting on
* SMP is a lower bound, by reason of under accounting.
*
* Worse, since the numbers are provided per CPU, they are sometimes
* interpreted per CPU, and that is nonsensical. A blocked task isn't strictly
* associated with any one particular CPU, it can wake to another CPU than it
* blocked on. This means the per CPU IO-wait number is meaningless.
*
* Task CPU affinities can make all that even more 'interesting'.
*/
unsigned int nr_iowait(void)
{
unsigned int i, sum = 0;
for_each_possible_cpu(i)
sum += nr_iowait_cpu(i);
return sum;
}
#ifdef CONFIG_SMP
/*
* sched_exec - execve() is a valuable balancing opportunity, because at
* this point the task has the smallest effective memory and cache footprint.
*/
void sched_exec(void)
{
struct task_struct *p = current;
struct migration_arg arg;
int dest_cpu;
scoped_guard (raw_spinlock_irqsave, &p->pi_lock) {
dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), WF_EXEC);
if (dest_cpu == smp_processor_id())
return;
if (unlikely(!cpu_active(dest_cpu)))
return;
arg = (struct migration_arg){ p, dest_cpu };
}
stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
}
#endif
DEFINE_PER_CPU(struct kernel_stat, kstat);
DEFINE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
EXPORT_PER_CPU_SYMBOL(kstat);
EXPORT_PER_CPU_SYMBOL(kernel_cpustat);
/*
* The function fair_sched_class.update_curr accesses the struct curr
* and its field curr->exec_start; when called from task_sched_runtime(),
* we observe a high rate of cache misses in practice.
* Prefetching this data results in improved performance.
*/
static inline void prefetch_curr_exec_start(struct task_struct *p)
{
#ifdef CONFIG_FAIR_GROUP_SCHED
struct sched_entity *curr = p->se.cfs_rq->curr;
#else
struct sched_entity *curr = task_rq(p)->cfs.curr;
#endif
prefetch(curr);
prefetch(&curr->exec_start);
}
/*
* Return accounted runtime for the task.
* In case the task is currently running, return the runtime plus current's
* pending runtime that have not been accounted yet.
*/
unsigned long long task_sched_runtime(struct task_struct *p)
{
struct rq_flags rf;
struct rq *rq;
u64 ns;
#if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
/*
* 64-bit doesn't need locks to atomically read a 64-bit value.
* So we have a optimization chance when the task's delta_exec is 0.
* Reading ->on_cpu is racy, but this is OK.
*
* If we race with it leaving CPU, we'll take a lock. So we're correct.
* If we race with it entering CPU, unaccounted time is 0. This is
* indistinguishable from the read occurring a few cycles earlier.
* If we see ->on_cpu without ->on_rq, the task is leaving, and has
* been accounted, so we're correct here as well.
*/
if (!p->on_cpu || !task_on_rq_queued(p))
return p->se.sum_exec_runtime;
#endif
rq = task_rq_lock(p, &rf);
/*
* Must be ->curr _and_ ->on_rq. If dequeued, we would
* project cycles that may never be accounted to this
* thread, breaking clock_gettime().
*/
if (task_current(rq, p) && task_on_rq_queued(p)) {
prefetch_curr_exec_start(p);
update_rq_clock(rq);
p->sched_class->update_curr(rq);
}
ns = p->se.sum_exec_runtime;
task_rq_unlock(rq, p, &rf);
return ns;
}
#ifdef CONFIG_SCHED_DEBUG
static u64 cpu_resched_latency(struct rq *rq)
{
int latency_warn_ms = READ_ONCE(sysctl_resched_latency_warn_ms);
u64 resched_latency, now = rq_clock(rq);
static bool warned_once;
if (sysctl_resched_latency_warn_once && warned_once)
return 0;
if (!need_resched() || !latency_warn_ms)
return 0;
if (system_state == SYSTEM_BOOTING)
return 0;
if (!rq->last_seen_need_resched_ns) {
rq->last_seen_need_resched_ns = now;
rq->ticks_without_resched = 0;
return 0;
}
rq->ticks_without_resched++;
resched_latency = now - rq->last_seen_need_resched_ns;
if (resched_latency <= latency_warn_ms * NSEC_PER_MSEC)
return 0;
warned_once = true;
return resched_latency;
}
static int __init setup_resched_latency_warn_ms(char *str)
{
long val;
if ((kstrtol(str, 0, &val))) {
pr_warn("Unable to set resched_latency_warn_ms\n");
return 1;
}
sysctl_resched_latency_warn_ms = val;
return 1;
}
__setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms);
#else
static inline u64 cpu_resched_latency(struct rq *rq) { return 0; }
#endif /* CONFIG_SCHED_DEBUG */
/*
* This function gets called by the timer code, with HZ frequency.
* We call it with interrupts disabled.
*/
void sched_tick(void)
{
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
struct task_struct *curr;
struct rq_flags rf;
unsigned long hw_pressure;
u64 resched_latency;
if (housekeeping_cpu(cpu, HK_TYPE_TICK))
arch_scale_freq_tick();
sched_clock_tick();
rq_lock(rq, &rf);
curr = rq->curr;
psi_account_irqtime(rq, curr, NULL);
update_rq_clock(rq);
hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure);
curr->sched_class->task_tick(rq, curr, 0);
if (sched_feat(LATENCY_WARN))
resched_latency = cpu_resched_latency(rq);
calc_global_load_tick(rq);
sched_core_tick(rq);
task_tick_mm_cid(rq, curr);
scx_tick(rq);
rq_unlock(rq, &rf);
if (sched_feat(LATENCY_WARN) && resched_latency)
resched_latency_warn(cpu, resched_latency);
perf_event_task_tick();
if (curr->flags & PF_WQ_WORKER)
wq_worker_tick(curr);
#ifdef CONFIG_SMP
if (!scx_switched_all()) {
rq->idle_balance = idle_cpu(cpu);
sched_balance_trigger(rq);
}
#endif
}
#ifdef CONFIG_NO_HZ_FULL
struct tick_work {
int cpu;
atomic_t state;
struct delayed_work work;
};
/* Values for ->state, see diagram below. */
#define TICK_SCHED_REMOTE_OFFLINE 0
#define TICK_SCHED_REMOTE_OFFLINING 1
#define TICK_SCHED_REMOTE_RUNNING 2
/*
* State diagram for ->state:
*
*
* TICK_SCHED_REMOTE_OFFLINE
* | ^
* | |
* | | sched_tick_remote()
* | |
* | |
* +--TICK_SCHED_REMOTE_OFFLINING
* | ^
* | |
* sched_tick_start() | | sched_tick_stop()
* | |
* V |
* TICK_SCHED_REMOTE_RUNNING
*
*
* Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
* and sched_tick_start() are happy to leave the state in RUNNING.
*/
static struct tick_work __percpu *tick_work_cpu;
static void sched_tick_remote(struct work_struct *work)
{
struct delayed_work *dwork = to_delayed_work(work);
struct tick_work *twork = container_of(dwork, struct tick_work, work);
int cpu = twork->cpu;
struct rq *rq = cpu_rq(cpu);
int os;
/*
* Handle the tick only if it appears the remote CPU is running in full
* dynticks mode. The check is racy by nature, but missing a tick or
* having one too much is no big deal because the scheduler tick updates
* statistics and checks timeslices in a time-independent way, regardless
* of when exactly it is running.
*/
if (tick_nohz_tick_stopped_cpu(cpu)) {
guard(rq_lock_irq)(rq);
struct task_struct *curr = rq->curr;
if (cpu_online(cpu)) {
update_rq_clock(rq);
if (!is_idle_task(curr)) {
/*
* Make sure the next tick runs within a
* reasonable amount of time.
*/
u64 delta = rq_clock_task(rq) - curr->se.exec_start;
WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
}
curr->sched_class->task_tick(rq, curr, 0);
calc_load_nohz_remote(rq);
}
}
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough
* to keep scheduler internal stats reasonably up to date. But
* first update state to reflect hotplug activity if required.
*/
os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
if (os == TICK_SCHED_REMOTE_RUNNING)
queue_delayed_work(system_unbound_wq, dwork, HZ);
}
static void sched_tick_start(int cpu)
{
int os;
struct tick_work *twork;
if (housekeeping_cpu(cpu, HK_TYPE_TICK))
return;
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
if (os == TICK_SCHED_REMOTE_OFFLINE) {
twork->cpu = cpu;
INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
queue_delayed_work(system_unbound_wq, &twork->work, HZ);
}
}
#ifdef CONFIG_HOTPLUG_CPU
static void sched_tick_stop(int cpu)
{
struct tick_work *twork;
int os;
if (housekeeping_cpu(cpu, HK_TYPE_TICK))
return;
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
/* There cannot be competing actions, but don't rely on stop-machine. */
os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
/* Don't cancel, as this would mess up the state machine. */
}
#endif /* CONFIG_HOTPLUG_CPU */
int __init sched_tick_offload_init(void)
{
tick_work_cpu = alloc_percpu(struct tick_work);
BUG_ON(!tick_work_cpu);
return 0;
}
#else /* !CONFIG_NO_HZ_FULL */
static inline void sched_tick_start(int cpu) { }
static inline void sched_tick_stop(int cpu) { }
#endif
#if defined(CONFIG_PREEMPTION) && (defined(CONFIG_DEBUG_PREEMPT) || \
defined(CONFIG_TRACE_PREEMPT_TOGGLE))
/*
* If the value passed in is equal to the current preempt count
* then we just disabled preemption. Start timing the latency.
*/
static inline void preempt_latency_start(int val)
{
if (preempt_count() == val) {
unsigned long ip = get_lock_parent_ip();
#ifdef CONFIG_DEBUG_PREEMPT
current->preempt_disable_ip = ip;
#endif
trace_preempt_off(CALLER_ADDR0, ip);
}
}
void preempt_count_add(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Underflow?
*/
if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
return;
#endif
__preempt_count_add(val);
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Spinlock count overflowing soon?
*/
DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
PREEMPT_MASK - 10);
#endif
preempt_latency_start(val);
}
EXPORT_SYMBOL(preempt_count_add);
NOKPROBE_SYMBOL(preempt_count_add);
/*
* If the value passed in equals to the current preempt count
* then we just enabled preemption. Stop timing the latency.
*/
static inline void preempt_latency_stop(int val)
{
if (preempt_count() == val)
trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
}
void preempt_count_sub(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Underflow?
*/
if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
return;
/*
* Is the spinlock portion underflowing?
*/
if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&
!(preempt_count() & PREEMPT_MASK)))
return;
#endif
preempt_latency_stop(val);
__preempt_count_sub(val);
}
EXPORT_SYMBOL(preempt_count_sub);
NOKPROBE_SYMBOL(preempt_count_sub);
#else
static inline void preempt_latency_start(int val) { }
static inline void preempt_latency_stop(int val) { }
#endif
static inline unsigned long get_preempt_disable_ip(struct task_struct *p)
{
#ifdef CONFIG_DEBUG_PREEMPT
return p->preempt_disable_ip;
#else
return 0;
#endif
}
/*
* Print scheduling while atomic bug:
*/
static noinline void __schedule_bug(struct task_struct *prev)
{
/* Save this before calling printk(), since that will clobber it */
unsigned long preempt_disable_ip = get_preempt_disable_ip(current);
if (oops_in_progress)
return;
printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
prev->comm, prev->pid, preempt_count());
debug_show_held_locks(prev);
print_modules();
if (irqs_disabled())
print_irqtrace_events(prev);
if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) {
pr_err("Preemption disabled at:");
print_ip_sym(KERN_ERR, preempt_disable_ip);
}
check_panic_on_warn("scheduling while atomic");
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
/*
* Various schedule()-time debugging checks and statistics:
*/
static inline void schedule_debug(struct task_struct *prev, bool preempt)
{
#ifdef CONFIG_SCHED_STACK_END_CHECK
if (task_stack_end_corrupted(prev))
panic("corrupted stack end detected inside scheduler\n");
if (task_scs_end_corrupted(prev))
panic("corrupted shadow stack detected inside scheduler\n");
#endif
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
if (!preempt && READ_ONCE(prev->__state) && prev->non_block_count) {
printk(KERN_ERR "BUG: scheduling in a non-blocking section: %s/%d/%i\n",
prev->comm, prev->pid, prev->non_block_count);
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
#endif
if (unlikely(in_atomic_preempt_off())) {
__schedule_bug(prev);
preempt_count_set(PREEMPT_DISABLED);
}
rcu_sleep_check();
SCHED_WARN_ON(ct_state() == CT_STATE_USER);
profile_hit(SCHED_PROFILING, __builtin_return_address(0));
schedstat_inc(this_rq()->sched_count);
}
static void prev_balance(struct rq *rq, struct task_struct *prev,
struct rq_flags *rf)
{
const struct sched_class *start_class = prev->sched_class;
const struct sched_class *class;
#ifdef CONFIG_SCHED_CLASS_EXT
/*
* SCX requires a balance() call before every pick_next_task() including
* when waking up from SCHED_IDLE. If @start_class is below SCX, start
* from SCX instead.
*/
if (scx_enabled() && sched_class_above(&ext_sched_class, start_class))
start_class = &ext_sched_class;
#endif
/*
* We must do the balancing pass before put_prev_task(), such
* that when we release the rq->lock the task is in the same
* state as before we took rq->lock.
*
* We can terminate the balance pass as soon as we know there is
* a runnable task of @class priority or higher.
*/
for_active_class_range(class, start_class, &idle_sched_class) {
if (class->balance && class->balance(rq, prev, rf))
break;
}
}
/*
* Pick up the highest-prio task:
*/
static inline struct task_struct *
__pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
const struct sched_class *class;
struct task_struct *p;
rq->dl_server = NULL;
if (scx_enabled())
goto restart;
/*
* Optimization: we know that if all tasks are in the fair class we can
* call that function directly, but only if the @prev task wasn't of a
* higher scheduling class, because otherwise those lose the
* opportunity to pull in more work from other CPUs.
*/
if (likely(!sched_class_above(prev->sched_class, &fair_sched_class) &&
rq->nr_running == rq->cfs.h_nr_running)) {
p = pick_next_task_fair(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
goto restart;
/* Assume the next prioritized class is idle_sched_class */
if (!p) {
p = pick_task_idle(rq);
put_prev_set_next_task(rq, prev, p);
}
return p;
}
restart:
prev_balance(rq, prev, rf);
for_each_active_class(class) {
if (class->pick_next_task) {
p = class->pick_next_task(rq, prev);
if (p)
return p;
} else {
p = class->pick_task(rq);
if (p) {
put_prev_set_next_task(rq, prev, p);
return p;
}
}
}
BUG(); /* The idle class should always have a runnable task. */
}
#ifdef CONFIG_SCHED_CORE
static inline bool is_task_rq_idle(struct task_struct *t)
{
return (task_rq(t)->idle == t);
}
static inline bool cookie_equals(struct task_struct *a, unsigned long cookie)
{
return is_task_rq_idle(a) || (a->core_cookie == cookie);
}
static inline bool cookie_match(struct task_struct *a, struct task_struct *b)
{
if (is_task_rq_idle(a) || is_task_rq_idle(b))
return true;
return a->core_cookie == b->core_cookie;
}
static inline struct task_struct *pick_task(struct rq *rq)
{
const struct sched_class *class;
struct task_struct *p;
rq->dl_server = NULL;
for_each_active_class(class) {
p = class->pick_task(rq);
if (p)
return p;
}
BUG(); /* The idle class should always have a runnable task. */
}
extern void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi);
static void queue_core_balance(struct rq *rq);
static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
struct task_struct *next, *p, *max = NULL;
const struct cpumask *smt_mask;
bool fi_before = false;
bool core_clock_updated = (rq == rq->core);
unsigned long cookie;
int i, cpu, occ = 0;
struct rq *rq_i;
bool need_sync;
if (!sched_core_enabled(rq))
return __pick_next_task(rq, prev, rf);
cpu = cpu_of(rq);
/* Stopper task is switching into idle, no need core-wide selection. */
if (cpu_is_offline(cpu)) {
/*
* Reset core_pick so that we don't enter the fastpath when
* coming online. core_pick would already be migrated to
* another cpu during offline.
*/
rq->core_pick = NULL;
rq->core_dl_server = NULL;
return __pick_next_task(rq, prev, rf);
}
/*
* If there were no {en,de}queues since we picked (IOW, the task
* pointers are all still valid), and we haven't scheduled the last
* pick yet, do so now.
*
* rq->core_pick can be NULL if no selection was made for a CPU because
* it was either offline or went offline during a sibling's core-wide
* selection. In this case, do a core-wide selection.
*/
if (rq->core->core_pick_seq == rq->core->core_task_seq &&
rq->core->core_pick_seq != rq->core_sched_seq &&
rq->core_pick) {
WRITE_ONCE(rq->core_sched_seq, rq->core->core_pick_seq);
next = rq->core_pick;
rq->dl_server = rq->core_dl_server;
rq->core_pick = NULL;
rq->core_dl_server = NULL;
goto out_set_next;
}
prev_balance(rq, prev, rf);
smt_mask = cpu_smt_mask(cpu);
need_sync = !!rq->core->core_cookie;
/* reset state */
rq->core->core_cookie = 0UL;
if (rq->core->core_forceidle_count) {
if (!core_clock_updated) {
update_rq_clock(rq->core);
core_clock_updated = true;
}
sched_core_account_forceidle(rq);
/* reset after accounting force idle */
rq->core->core_forceidle_start = 0;
rq->core->core_forceidle_count = 0;
rq->core->core_forceidle_occupation = 0;
need_sync = true;
fi_before = true;
}
/*
* core->core_task_seq, core->core_pick_seq, rq->core_sched_seq
*
* @task_seq guards the task state ({en,de}queues)
* @pick_seq is the @task_seq we did a selection on
* @sched_seq is the @pick_seq we scheduled
*
* However, preemptions can cause multiple picks on the same task set.
* 'Fix' this by also increasing @task_seq for every pick.
*/
rq->core->core_task_seq++;
/*
* Optimize for common case where this CPU has no cookies
* and there are no cookied tasks running on siblings.
*/
if (!need_sync) {
next = pick_task(rq);
if (!next->core_cookie) {
rq->core_pick = NULL;
rq->core_dl_server = NULL;
/*
* For robustness, update the min_vruntime_fi for
* unconstrained picks as well.
*/
WARN_ON_ONCE(fi_before);
task_vruntime_update(rq, next, false);
goto out_set_next;
}
}
/*
* For each thread: do the regular task pick and find the max prio task
* amongst them.
*
* Tie-break prio towards the current CPU
*/
for_each_cpu_wrap(i, smt_mask, cpu) {
rq_i = cpu_rq(i);
/*
* Current cpu always has its clock updated on entrance to
* pick_next_task(). If the current cpu is not the core,
* the core may also have been updated above.
*/
if (i != cpu && (rq_i != rq->core || !core_clock_updated))
update_rq_clock(rq_i);
rq_i->core_pick = p = pick_task(rq_i);
rq_i->core_dl_server = rq_i->dl_server;
if (!max || prio_less(max, p, fi_before))
max = p;
}
cookie = rq->core->core_cookie = max->core_cookie;
/*
* For each thread: try and find a runnable task that matches @max or
* force idle.
*/
for_each_cpu(i, smt_mask) {
rq_i = cpu_rq(i);
p = rq_i->core_pick;
if (!cookie_equals(p, cookie)) {
p = NULL;
if (cookie)
p = sched_core_find(rq_i, cookie);
if (!p)
p = idle_sched_class.pick_task(rq_i);
}
rq_i->core_pick = p;
rq_i->core_dl_server = NULL;
if (p == rq_i->idle) {
if (rq_i->nr_running) {
rq->core->core_forceidle_count++;
if (!fi_before)
rq->core->core_forceidle_seq++;
}
} else {
occ++;
}
}
if (schedstat_enabled() && rq->core->core_forceidle_count) {
rq->core->core_forceidle_start = rq_clock(rq->core);
rq->core->core_forceidle_occupation = occ;
}
rq->core->core_pick_seq = rq->core->core_task_seq;
next = rq->core_pick;
rq->core_sched_seq = rq->core->core_pick_seq;
/* Something should have been selected for current CPU */
WARN_ON_ONCE(!next);
/*
* Reschedule siblings
*
* NOTE: L1TF -- at this point we're no longer running the old task and
* sending an IPI (below) ensures the sibling will no longer be running
* their task. This ensures there is no inter-sibling overlap between
* non-matching user state.
*/
for_each_cpu(i, smt_mask) {
rq_i = cpu_rq(i);
/*
* An online sibling might have gone offline before a task
* could be picked for it, or it might be offline but later
* happen to come online, but its too late and nothing was
* picked for it. That's Ok - it will pick tasks for itself,
* so ignore it.
*/
if (!rq_i->core_pick)
continue;
/*
* Update for new !FI->FI transitions, or if continuing to be in !FI:
* fi_before fi update?
* 0 0 1
* 0 1 1
* 1 0 1
* 1 1 0
*/
if (!(fi_before && rq->core->core_forceidle_count))
task_vruntime_update(rq_i, rq_i->core_pick, !!rq->core->core_forceidle_count);
rq_i->core_pick->core_occupation = occ;
if (i == cpu) {
rq_i->core_pick = NULL;
rq_i->core_dl_server = NULL;
continue;
}
/* Did we break L1TF mitigation requirements? */
WARN_ON_ONCE(!cookie_match(next, rq_i->core_pick));
if (rq_i->curr == rq_i->core_pick) {
rq_i->core_pick = NULL;
rq_i->core_dl_server = NULL;
continue;
}
resched_curr(rq_i);
}
out_set_next:
put_prev_set_next_task(rq, prev, next);
if (rq->core->core_forceidle_count && next == rq->idle)
queue_core_balance(rq);
return next;
}
static bool try_steal_cookie(int this, int that)
{
struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
struct task_struct *p;
unsigned long cookie;
bool success = false;
guard(irq)();
guard(double_rq_lock)(dst, src);
cookie = dst->core->core_cookie;
if (!cookie)
return false;
if (dst->curr != dst->idle)
return false;
p = sched_core_find(src, cookie);
if (!p)
return false;
do {
if (p == src->core_pick || p == src->curr)
goto next;
if (!is_cpu_allowed(p, this))
goto next;
if (p->core_occupation > dst->idle->core_occupation)
goto next;
/*
* sched_core_find() and sched_core_next() will ensure
* that task @p is not throttled now, we also need to
* check whether the runqueue of the destination CPU is
* being throttled.
*/
if (sched_task_is_throttled(p, this))
goto next;
deactivate_task(src, p, 0);
set_task_cpu(p, this);
activate_task(dst, p, 0);
resched_curr(dst);
success = true;
break;
next:
p = sched_core_next(p, cookie);
} while (p);
return success;
}
static bool steal_cookie_task(int cpu, struct sched_domain *sd)
{
int i;
for_each_cpu_wrap(i, sched_domain_span(sd), cpu + 1) {
if (i == cpu)
continue;
if (need_resched())
break;
if (try_steal_cookie(cpu, i))
return true;
}
return false;
}
static void sched_core_balance(struct rq *rq)
{
struct sched_domain *sd;
int cpu = cpu_of(rq);
guard(preempt)();
guard(rcu)();
raw_spin_rq_unlock_irq(rq);
for_each_domain(cpu, sd) {
if (need_resched())
break;
if (steal_cookie_task(cpu, sd))
break;
}
raw_spin_rq_lock_irq(rq);
}
static DEFINE_PER_CPU(struct balance_callback, core_balance_head);
static void queue_core_balance(struct rq *rq)
{
if (!sched_core_enabled(rq))
return;
if (!rq->core->core_cookie)
return;
if (!rq->nr_running) /* not forced idle */
return;
queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance);
}
DEFINE_LOCK_GUARD_1(core_lock, int,
sched_core_lock(*_T->lock, &_T->flags),
sched_core_unlock(*_T->lock, &_T->flags),
unsigned long flags)
static void sched_core_cpu_starting(unsigned int cpu)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
int t;
guard(core_lock)(&cpu);
WARN_ON_ONCE(rq->core != rq);
/* if we're the first, we'll be our own leader */
if (cpumask_weight(smt_mask) == 1)
return;
/* find the leader */
for_each_cpu(t, smt_mask) {
if (t == cpu)
continue;
rq = cpu_rq(t);
if (rq->core == rq) {
core_rq = rq;
break;
}
}
if (WARN_ON_ONCE(!core_rq)) /* whoopsie */
return;
/* install and validate core_rq */
for_each_cpu(t, smt_mask) {
rq = cpu_rq(t);
if (t == cpu)
rq->core = core_rq;
WARN_ON_ONCE(rq->core != core_rq);
}
}
static void sched_core_cpu_deactivate(unsigned int cpu)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
int t;
guard(core_lock)(&cpu);
/* if we're the last man standing, nothing to do */
if (cpumask_weight(smt_mask) == 1) {
WARN_ON_ONCE(rq->core != rq);
return;
}
/* if we're not the leader, nothing to do */
if (rq->core != rq)
return;
/* find a new leader */
for_each_cpu(t, smt_mask) {
if (t == cpu)
continue;
core_rq = cpu_rq(t);
break;
}
if (WARN_ON_ONCE(!core_rq)) /* impossible */
return;
/* copy the shared state to the new leader */
core_rq->core_task_seq = rq->core_task_seq;
core_rq->core_pick_seq = rq->core_pick_seq;
core_rq->core_cookie = rq->core_cookie;
core_rq->core_forceidle_count = rq->core_forceidle_count;
core_rq->core_forceidle_seq = rq->core_forceidle_seq;
core_rq->core_forceidle_occupation = rq->core_forceidle_occupation;
/*
* Accounting edge for forced idle is handled in pick_next_task().
* Don't need another one here, since the hotplug thread shouldn't
* have a cookie.
*/
core_rq->core_forceidle_start = 0;
/* install new leader */
for_each_cpu(t, smt_mask) {
rq = cpu_rq(t);
rq->core = core_rq;
}
}
static inline void sched_core_cpu_dying(unsigned int cpu)
{
struct rq *rq = cpu_rq(cpu);
if (rq->core != rq)
rq->core = rq;
}
#else /* !CONFIG_SCHED_CORE */
static inline void sched_core_cpu_starting(unsigned int cpu) {}
static inline void sched_core_cpu_deactivate(unsigned int cpu) {}
static inline void sched_core_cpu_dying(unsigned int cpu) {}
static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
return __pick_next_task(rq, prev, rf);
}
#endif /* CONFIG_SCHED_CORE */
/*
* Constants for the sched_mode argument of __schedule().
*
* The mode argument allows RT enabled kernels to differentiate a
* preemption from blocking on an 'sleeping' spin/rwlock.
*/
#define SM_IDLE (-1)
#define SM_NONE 0
#define SM_PREEMPT 1
#define SM_RTLOCK_WAIT 2
/*
* __schedule() is the main scheduler function.
*
* The main means of driving the scheduler and thus entering this function are:
*
* 1. Explicit blocking: mutex, semaphore, waitqueue, etc.
*
* 2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
* paths. For example, see arch/x86/entry_64.S.
*
* To drive preemption between tasks, the scheduler sets the flag in timer
* interrupt handler sched_tick().
*
* 3. Wakeups don't really cause entry into schedule(). They add a
* task to the run-queue and that's it.
*
* Now, if the new task added to the run-queue preempts the current
* task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets
* called on the nearest possible occasion:
*
* - If the kernel is preemptible (CONFIG_PREEMPTION=y):
*
* - in syscall or exception context, at the next outmost
* preempt_enable(). (this might be as soon as the wake_up()'s
* spin_unlock()!)
*
* - in IRQ context, return from interrupt-handler to
* preemptible context
*
* - If the kernel is not preemptible (CONFIG_PREEMPTION is not set)
* then at the next:
*
* - cond_resched() call
* - explicit schedule() call
* - return from syscall or exception to user-space
* - return from interrupt-handler to user-space
*
* WARNING: must be called with preemption disabled!
*/
static void __sched notrace __schedule(int sched_mode)
{
struct task_struct *prev, *next;
/*
* On PREEMPT_RT kernel, SM_RTLOCK_WAIT is noted
* as a preemption by schedule_debug() and RCU.
*/
bool preempt = sched_mode > SM_NONE;
unsigned long *switch_count;
unsigned long prev_state;
struct rq_flags rf;
struct rq *rq;
int cpu;
cpu = smp_processor_id();
rq = cpu_rq(cpu);
prev = rq->curr;
schedule_debug(prev, preempt);
if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
hrtick_clear(rq);
local_irq_disable();
rcu_note_context_switch(preempt);
/*
* Make sure that signal_pending_state()->signal_pending() below
* can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
* done by the caller to avoid the race with signal_wake_up():
*
* __set_current_state(@state) signal_wake_up()
* schedule() set_tsk_thread_flag(p, TIF_SIGPENDING)
* wake_up_state(p, state)
* LOCK rq->lock LOCK p->pi_state
* smp_mb__after_spinlock() smp_mb__after_spinlock()
* if (signal_pending_state()) if (p->state & @state)
*
* Also, the membarrier system call requires a full memory barrier
* after coming from user-space, before storing to rq->curr; this
* barrier matches a full barrier in the proximity of the membarrier
* system call exit.
*/
rq_lock(rq, &rf);
smp_mb__after_spinlock();
/* Promote REQ to ACT */
rq->clock_update_flags <<= 1;
update_rq_clock(rq);
rq->clock_update_flags = RQCF_UPDATED;
switch_count = &prev->nivcsw;
/* Task state changes only considers SM_PREEMPT as preemption */
preempt = sched_mode == SM_PREEMPT;
/*
* We must load prev->state once (task_struct::state is volatile), such
* that we form a control dependency vs deactivate_task() below.
*/
prev_state = READ_ONCE(prev->__state);
if (sched_mode == SM_IDLE) {
/* SCX must consult the BPF scheduler to tell if rq is empty */
if (!rq->nr_running && !scx_enabled()) {
next = prev;
goto picked;
}
} else if (!preempt && prev_state) {
if (signal_pending_state(prev_state, prev)) {
WRITE_ONCE(prev->__state, TASK_RUNNING);
} else {
int flags = DEQUEUE_NOCLOCK;
prev->sched_contributes_to_load =
(prev_state & TASK_UNINTERRUPTIBLE) &&
!(prev_state & TASK_NOLOAD) &&
!(prev_state & TASK_FROZEN);
if (unlikely(is_special_task_state(prev_state)))
flags |= DEQUEUE_SPECIAL;
/*
* __schedule() ttwu()
* prev_state = prev->state; if (p->on_rq && ...)
* if (prev_state) goto out;
* p->on_rq = 0; smp_acquire__after_ctrl_dep();
* p->state = TASK_WAKING
*
* Where __schedule() and ttwu() have matching control dependencies.
*
* After this, schedule() must not care about p->state any more.
*/
block_task(rq, prev, flags);
}
switch_count = &prev->nvcsw;
}
next = pick_next_task(rq, prev, &rf);
picked:
clear_tsk_need_resched(prev);
clear_preempt_need_resched();
#ifdef CONFIG_SCHED_DEBUG
rq->last_seen_need_resched_ns = 0;
#endif
if (likely(prev != next)) {
rq->nr_switches++;
/*
* RCU users of rcu_dereference(rq->curr) may not see
* changes to task_struct made by pick_next_task().
*/
RCU_INIT_POINTER(rq->curr, next);
/*
* The membarrier system call requires each architecture
* to have a full memory barrier after updating
* rq->curr, before returning to user-space.
*
* Here are the schemes providing that barrier on the
* various architectures:
* - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC,
* RISC-V. switch_mm() relies on membarrier_arch_switch_mm()
* on PowerPC and on RISC-V.
* - finish_lock_switch() for weakly-ordered
* architectures where spin_unlock is a full barrier,
* - switch_to() for arm64 (weakly-ordered, spin_unlock
* is a RELEASE barrier),
*
* The barrier matches a full barrier in the proximity of
* the membarrier system call entry.
*
* On RISC-V, this barrier pairing is also needed for the
* SYNC_CORE command when switching between processes, cf.
* the inline comments in membarrier_arch_switch_mm().
*/
++*switch_count;
migrate_disable_switch(rq, prev);
psi_account_irqtime(rq, prev, next);
psi_sched_switch(prev, next, !task_on_rq_queued(prev));
trace_sched_switch(preempt, prev, next, prev_state);
/* Also unlocks the rq: */
rq = context_switch(rq, prev, next, &rf);
} else {
rq_unpin_lock(rq, &rf);
__balance_callbacks(rq);
raw_spin_rq_unlock_irq(rq);
}
}
void __noreturn do_task_dead(void)
{
/* Causes final put_task_struct in finish_task_switch(): */
set_special_state(TASK_DEAD);
/* Tell freezer to ignore us: */
current->flags |= PF_NOFREEZE;
__schedule(SM_NONE);
BUG();
/* Avoid "noreturn function does return" - but don't continue if BUG() is a NOP: */
for (;;)
cpu_relax();
}
static inline void sched_submit_work(struct task_struct *tsk)
{
static DEFINE_WAIT_OVERRIDE_MAP(sched_map, LD_WAIT_CONFIG);
unsigned int task_flags;
/*
* Establish LD_WAIT_CONFIG context to ensure none of the code called
* will use a blocking primitive -- which would lead to recursion.
*/
lock_map_acquire_try(&sched_map);
task_flags = tsk->flags;
/*
* If a worker goes to sleep, notify and ask workqueue whether it
* wants to wake up a task to maintain concurrency.
*/
if (task_flags & PF_WQ_WORKER)
wq_worker_sleeping(tsk);
else if (task_flags & PF_IO_WORKER)
io_wq_worker_sleeping(tsk);
/*
* spinlock and rwlock must not flush block requests. This will
* deadlock if the callback attempts to acquire a lock which is
* already acquired.
*/
SCHED_WARN_ON(current->__state & TASK_RTLOCK_WAIT);
/*
* If we are going to sleep and we have plugged IO queued,
* make sure to submit it to avoid deadlocks.
*/
blk_flush_plug(tsk->plug, true);
lock_map_release(&sched_map);
}
static void sched_update_worker(struct task_struct *tsk)
{
if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER | PF_BLOCK_TS)) {
if (tsk->flags & PF_BLOCK_TS)
blk_plug_invalidate_ts(tsk);
if (tsk->flags & PF_WQ_WORKER)
wq_worker_running(tsk);
else if (tsk->flags & PF_IO_WORKER)
io_wq_worker_running(tsk);
}
}
static __always_inline void __schedule_loop(int sched_mode)
{
do {
preempt_disable();
__schedule(sched_mode);
sched_preempt_enable_no_resched();
} while (need_resched());
}
asmlinkage __visible void __sched schedule(void)
{
struct task_struct *tsk = current;
#ifdef CONFIG_RT_MUTEXES
lockdep_assert(!tsk->sched_rt_mutex);
#endif
if (!task_is_running(tsk))
sched_submit_work(tsk);
__schedule_loop(SM_NONE);
sched_update_worker(tsk);
}
EXPORT_SYMBOL(schedule);
/*
* synchronize_rcu_tasks() makes sure that no task is stuck in preempted
* state (have scheduled out non-voluntarily) by making sure that all
* tasks have either left the run queue or have gone into user space.
* As idle tasks do not do either, they must not ever be preempted
* (schedule out non-voluntarily).
*
* schedule_idle() is similar to schedule_preempt_disable() except that it
* never enables preemption because it does not call sched_submit_work().
*/
void __sched schedule_idle(void)
{
/*
* As this skips calling sched_submit_work(), which the idle task does
* regardless because that function is a NOP when the task is in a
* TASK_RUNNING state, make sure this isn't used someplace that the
* current task can be in any other state. Note, idle is always in the
* TASK_RUNNING state.
*/
WARN_ON_ONCE(current->__state);
do {
__schedule(SM_IDLE);
} while (need_resched());
}
#if defined(CONFIG_CONTEXT_TRACKING_USER) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_USER_OFFSTACK)
asmlinkage __visible void __sched schedule_user(void)
{
/*
* If we come here after a random call to set_need_resched(),
* or we have been woken up remotely but the IPI has not yet arrived,
* we haven't yet exited the RCU idle mode. Do it here manually until
* we find a better solution.
*
* NB: There are buggy callers of this function. Ideally we
* should warn if prev_state != CT_STATE_USER, but that will trigger
* too frequently to make sense yet.
*/
enum ctx_state prev_state = exception_enter();
schedule();
exception_exit(prev_state);
}
#endif
/**
* schedule_preempt_disabled - called with preemption disabled
*
* Returns with preemption disabled. Note: preempt_count must be 1
*/
void __sched schedule_preempt_disabled(void)
{
sched_preempt_enable_no_resched();
schedule();
preempt_disable();
}
#ifdef CONFIG_PREEMPT_RT
void __sched notrace schedule_rtlock(void)
{
__schedule_loop(SM_RTLOCK_WAIT);
}
NOKPROBE_SYMBOL(schedule_rtlock);
#endif
static void __sched notrace preempt_schedule_common(void)
{
do {
/*
* Because the function tracer can trace preempt_count_sub()
* and it also uses preempt_enable/disable_notrace(), if
* NEED_RESCHED is set, the preempt_enable_notrace() called
* by the function tracer will call this function again and
* cause infinite recursion.
*
* Preemption must be disabled here before the function
* tracer can trace. Break up preempt_disable() into two
* calls. One to disable preemption without fear of being
* traced. The other to still record the preemption latency,
* which can also be traced by the function tracer.
*/
preempt_disable_notrace();
preempt_latency_start(1);
__schedule(SM_PREEMPT);
preempt_latency_stop(1);
preempt_enable_no_resched_notrace();
/*
* Check again in case we missed a preemption opportunity
* between schedule and now.
*/
} while (need_resched());
}
#ifdef CONFIG_PREEMPTION
/*
* This is the entry point to schedule() from in-kernel preemption
* off of preempt_enable.
*/
asmlinkage __visible void __sched notrace preempt_schedule(void)
{
/*
* If there is a non-zero preempt_count or interrupts are disabled,
* we do not want to preempt the current task. Just return..
*/
if (likely(!preemptible()))
return;
preempt_schedule_common();
}
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_dynamic_enabled
#define preempt_schedule_dynamic_enabled preempt_schedule
#define preempt_schedule_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule);
void __sched notrace dynamic_preempt_schedule(void)
{
if (!static_branch_unlikely(&sk_dynamic_preempt_schedule))
return;
preempt_schedule();
}
NOKPROBE_SYMBOL(dynamic_preempt_schedule);
EXPORT_SYMBOL(dynamic_preempt_schedule);
#endif
#endif
/**
* preempt_schedule_notrace - preempt_schedule called by tracing
*
* The tracing infrastructure uses preempt_enable_notrace to prevent
* recursion and tracing preempt enabling caused by the tracing
* infrastructure itself. But as tracing can happen in areas coming
* from userspace or just about to enter userspace, a preempt enable
* can occur before user_exit() is called. This will cause the scheduler
* to be called when the system is still in usermode.
*
* To prevent this, the preempt_enable_notrace will use this function
* instead of preempt_schedule() to exit user context if needed before
* calling the scheduler.
*/
asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
{
enum ctx_state prev_ctx;
if (likely(!preemptible()))
return;
do {
/*
* Because the function tracer can trace preempt_count_sub()
* and it also uses preempt_enable/disable_notrace(), if
* NEED_RESCHED is set, the preempt_enable_notrace() called
* by the function tracer will call this function again and
* cause infinite recursion.
*
* Preemption must be disabled here before the function
* tracer can trace. Break up preempt_disable() into two
* calls. One to disable preemption without fear of being
* traced. The other to still record the preemption latency,
* which can also be traced by the function tracer.
*/
preempt_disable_notrace();
preempt_latency_start(1);
/*
* Needs preempt disabled in case user_exit() is traced
* and the tracer calls preempt_enable_notrace() causing
* an infinite recursion.
*/
prev_ctx = exception_enter();
__schedule(SM_PREEMPT);
exception_exit(prev_ctx);
preempt_latency_stop(1);
preempt_enable_no_resched_notrace();
} while (need_resched());
}
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_notrace_dynamic_enabled
#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
#define preempt_schedule_notrace_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule_notrace);
void __sched notrace dynamic_preempt_schedule_notrace(void)
{
if (!static_branch_unlikely(&sk_dynamic_preempt_schedule_notrace))
return;
preempt_schedule_notrace();
}
NOKPROBE_SYMBOL(dynamic_preempt_schedule_notrace);
EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
#endif
#endif
#endif /* CONFIG_PREEMPTION */
/*
* This is the entry point to schedule() from kernel preemption
* off of IRQ context.
* Note, that this is called and return with IRQs disabled. This will
* protect us against recursive calling from IRQ contexts.
*/
asmlinkage __visible void __sched preempt_schedule_irq(void)
{
enum ctx_state prev_state;
/* Catch callers which need to be fixed */
BUG_ON(preempt_count() || !irqs_disabled());
prev_state = exception_enter();
do {
preempt_disable();
local_irq_enable();
__schedule(SM_PREEMPT);
local_irq_disable();
sched_preempt_enable_no_resched();
} while (need_resched());
exception_exit(prev_state);
}
int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
void *key)
{
WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~(WF_SYNC|WF_CURRENT_CPU));
return try_to_wake_up(curr->private, mode, wake_flags);
}
EXPORT_SYMBOL(default_wake_function);
void __setscheduler_prio(struct task_struct *p, int prio)
{
if (dl_prio(prio))
p->sched_class = &dl_sched_class;
else if (rt_prio(prio))
p->sched_class = &rt_sched_class;
#ifdef CONFIG_SCHED_CLASS_EXT
else if (task_should_scx(p))
p->sched_class = &ext_sched_class;
#endif
else
p->sched_class = &fair_sched_class;
p->prio = prio;
}
#ifdef CONFIG_RT_MUTEXES
/*
* Would be more useful with typeof()/auto_type but they don't mix with
* bit-fields. Since it's a local thing, use int. Keep the generic sounding
* name such that if someone were to implement this function we get to compare
* notes.
*/
#define fetch_and_set(x, v) ({ int _x = (x); (x) = (v); _x; })
void rt_mutex_pre_schedule(void)
{
lockdep_assert(!fetch_and_set(current->sched_rt_mutex, 1));
sched_submit_work(current);
}
void rt_mutex_schedule(void)
{
lockdep_assert(current->sched_rt_mutex);
__schedule_loop(SM_NONE);
}
void rt_mutex_post_schedule(void)
{
sched_update_worker(current);
lockdep_assert(fetch_and_set(current->sched_rt_mutex, 0));
}
/*
* rt_mutex_setprio - set the current priority of a task
* @p: task to boost
* @pi_task: donor task
*
* This function changes the 'effective' priority of a task. It does
* not touch ->normal_prio like __setscheduler().
*
* Used by the rt_mutex code to implement priority inheritance
* logic. Call site only calls if the priority of the task changed.
*/
void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
{
int prio, oldprio, queued, running, queue_flag =
DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
const struct sched_class *prev_class;
struct rq_flags rf;
struct rq *rq;
/* XXX used to be waiter->prio, not waiter->task->prio */
prio = __rt_effective_prio(pi_task, p->normal_prio);
/*
* If nothing changed; bail early.
*/
if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
return;
rq = __task_rq_lock(p, &rf);
update_rq_clock(rq);
/*
* Set under pi_lock && rq->lock, such that the value can be used under
* either lock.
*
* Note that there is loads of tricky to make this pointer cache work
* right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
* ensure a task is de-boosted (pi_task is set to NULL) before the
* task is allowed to run again (and can exit). This ensures the pointer
* points to a blocked task -- which guarantees the task is present.
*/
p->pi_top_task = pi_task;
/*
* For FIFO/RR we only need to set prio, if that matches we're done.
*/
if (prio == p->prio && !dl_prio(prio))
goto out_unlock;
/*
* Idle task boosting is a no-no in general. There is one
* exception, when PREEMPT_RT and NOHZ is active:
*
* The idle task calls get_next_timer_interrupt() and holds
* the timer wheel base->lock on the CPU and another CPU wants
* to access the timer (probably to cancel it). We can safely
* ignore the boosting request, as the idle CPU runs this code
* with interrupts disabled and will complete the lock
* protected section without being interrupted. So there is no
* real need to boost.
*/
if (unlikely(p == rq->idle)) {
WARN_ON(p != rq->curr);
WARN_ON(p->pi_blocked_on);
goto out_unlock;
}
trace_sched_pi_setprio(p, pi_task);
oldprio = p->prio;
if (oldprio == prio)
queue_flag &= ~DEQUEUE_MOVE;
prev_class = p->sched_class;
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued)
dequeue_task(rq, p, queue_flag);
if (running)
put_prev_task(rq, p);
/*
* Boosting condition are:
* 1. -rt task is running and holds mutex A
* --> -dl task blocks on mutex A
*
* 2. -dl task is running and holds mutex A
* --> -dl task blocks on mutex A and could preempt the
* running task
*/
if (dl_prio(prio)) {
if (!dl_prio(p->normal_prio) ||
(pi_task && dl_prio(pi_task->prio) &&
dl_entity_preempt(&pi_task->dl, &p->dl))) {
p->dl.pi_se = pi_task->dl.pi_se;
queue_flag |= ENQUEUE_REPLENISH;
} else {
p->dl.pi_se = &p->dl;
}
} else if (rt_prio(prio)) {
if (dl_prio(oldprio))
p->dl.pi_se = &p->dl;
if (oldprio < prio)
queue_flag |= ENQUEUE_HEAD;
} else {
if (dl_prio(oldprio))
p->dl.pi_se = &p->dl;
if (rt_prio(oldprio))
p->rt.timeout = 0;
}
__setscheduler_prio(p, prio);
check_class_changing(rq, p, prev_class);
if (queued)
enqueue_task(rq, p, queue_flag);
if (running)
set_next_task(rq, p);
check_class_changed(rq, p, prev_class, oldprio);
out_unlock:
/* Avoid rq from going away on us: */
preempt_disable();
rq_unpin_lock(rq, &rf);
__balance_callbacks(rq);
raw_spin_rq_unlock(rq);
preempt_enable();
}
#endif
#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
int __sched __cond_resched(void)
{
if (should_resched(0)) {
preempt_schedule_common();
return 1;
}
/*
* In preemptible kernels, ->rcu_read_lock_nesting tells the tick
* whether the current CPU is in an RCU read-side critical section,
* so the tick can report quiescent states even for CPUs looping
* in kernel context. In contrast, in non-preemptible kernels,
* RCU readers leave no in-memory hints, which means that CPU-bound
* processes executing in kernel context might never report an
* RCU quiescent state. Therefore, the following code causes
* cond_resched() to report a quiescent state, but only when RCU
* is in urgent need of one.
*/
#ifndef CONFIG_PREEMPT_RCU
rcu_all_qs();
#endif
return 0;
}
EXPORT_SYMBOL(__cond_resched);
#endif
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define cond_resched_dynamic_enabled __cond_resched
#define cond_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(cond_resched);
#define might_resched_dynamic_enabled __cond_resched
#define might_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
int __sched dynamic_cond_resched(void)
{
klp_sched_try_switch();
if (!static_branch_unlikely(&sk_dynamic_cond_resched))
return 0;
return __cond_resched();
}
EXPORT_SYMBOL(dynamic_cond_resched);
static DEFINE_STATIC_KEY_FALSE(sk_dynamic_might_resched);
int __sched dynamic_might_resched(void)
{
if (!static_branch_unlikely(&sk_dynamic_might_resched))
return 0;
return __cond_resched();
}
EXPORT_SYMBOL(dynamic_might_resched);
#endif
#endif
/*
* __cond_resched_lock() - if a reschedule is pending, drop the given lock,
* call schedule, and on return reacquire the lock.
*
* This works OK both with and without CONFIG_PREEMPTION. We do strange low-level
* operations here to prevent schedule() from being called twice (once via
* spin_unlock(), once by hand).
*/
int __cond_resched_lock(spinlock_t *lock)
{
int resched = should_resched(PREEMPT_LOCK_OFFSET);
int ret = 0;
lockdep_assert_held(lock);
if (spin_needbreak(lock) || resched) {
spin_unlock(lock);
if (!_cond_resched())
cpu_relax();
ret = 1;
spin_lock(lock);
}
return ret;
}
EXPORT_SYMBOL(__cond_resched_lock);
int __cond_resched_rwlock_read(rwlock_t *lock)
{
int resched = should_resched(PREEMPT_LOCK_OFFSET);
int ret = 0;
lockdep_assert_held_read(lock);
if (rwlock_needbreak(lock) || resched) {
read_unlock(lock);
if (!_cond_resched())
cpu_relax();
ret = 1;
read_lock(lock);
}
return ret;
}
EXPORT_SYMBOL(__cond_resched_rwlock_read);
int __cond_resched_rwlock_write(rwlock_t *lock)
{
int resched = should_resched(PREEMPT_LOCK_OFFSET);
int ret = 0;
lockdep_assert_held_write(lock);
if (rwlock_needbreak(lock) || resched) {
write_unlock(lock);
if (!_cond_resched())
cpu_relax();
ret = 1;
write_lock(lock);
}
return ret;
}
EXPORT_SYMBOL(__cond_resched_rwlock_write);
#ifdef CONFIG_PREEMPT_DYNAMIC
#ifdef CONFIG_GENERIC_ENTRY
#include <linux/entry-common.h>
#endif
/*
* SC:cond_resched
* SC:might_resched
* SC:preempt_schedule
* SC:preempt_schedule_notrace
* SC:irqentry_exit_cond_resched
*
*
* NONE:
* cond_resched <- __cond_resched
* might_resched <- RET0
* preempt_schedule <- NOP
* preempt_schedule_notrace <- NOP
* irqentry_exit_cond_resched <- NOP
*
* VOLUNTARY:
* cond_resched <- __cond_resched
* might_resched <- __cond_resched
* preempt_schedule <- NOP
* preempt_schedule_notrace <- NOP
* irqentry_exit_cond_resched <- NOP
*
* FULL:
* cond_resched <- RET0
* might_resched <- RET0
* preempt_schedule <- preempt_schedule
* preempt_schedule_notrace <- preempt_schedule_notrace
* irqentry_exit_cond_resched <- irqentry_exit_cond_resched
*/
enum {
preempt_dynamic_undefined = -1,
preempt_dynamic_none,
preempt_dynamic_voluntary,
preempt_dynamic_full,
};
int preempt_dynamic_mode = preempt_dynamic_undefined;
int sched_dynamic_mode(const char *str)
{
if (!strcmp(str, "none"))
return preempt_dynamic_none;
if (!strcmp(str, "voluntary"))
return preempt_dynamic_voluntary;
if (!strcmp(str, "full"))
return preempt_dynamic_full;
return -EINVAL;
}
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
#define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
#define preempt_dynamic_enable(f) static_key_enable(&sk_dynamic_##f.key)
#define preempt_dynamic_disable(f) static_key_disable(&sk_dynamic_##f.key)
#else
#error "Unsupported PREEMPT_DYNAMIC mechanism"
#endif
static DEFINE_MUTEX(sched_dynamic_mutex);
static bool klp_override;
static void __sched_dynamic_update(int mode)
{
/*
* Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
* the ZERO state, which is invalid.
*/
if (!klp_override)
preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
preempt_dynamic_enable(irqentry_exit_cond_resched);
switch (mode) {
case preempt_dynamic_none:
if (!klp_override)
preempt_dynamic_enable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
preempt_dynamic_disable(irqentry_exit_cond_resched);
if (mode != preempt_dynamic_mode)
pr_info("Dynamic Preempt: none\n");
break;
case preempt_dynamic_voluntary:
if (!klp_override)
preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
preempt_dynamic_disable(irqentry_exit_cond_resched);
if (mode != preempt_dynamic_mode)
pr_info("Dynamic Preempt: voluntary\n");
break;
case preempt_dynamic_full:
if (!klp_override)
preempt_dynamic_disable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
preempt_dynamic_enable(irqentry_exit_cond_resched);
if (mode != preempt_dynamic_mode)
pr_info("Dynamic Preempt: full\n");
break;
}
preempt_dynamic_mode = mode;
}
void sched_dynamic_update(int mode)
{
mutex_lock(&sched_dynamic_mutex);
__sched_dynamic_update(mode);
mutex_unlock(&sched_dynamic_mutex);
}
#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
static int klp_cond_resched(void)
{
__klp_sched_try_switch();
return __cond_resched();
}
void sched_dynamic_klp_enable(void)
{
mutex_lock(&sched_dynamic_mutex);
klp_override = true;
static_call_update(cond_resched, klp_cond_resched);
mutex_unlock(&sched_dynamic_mutex);
}
void sched_dynamic_klp_disable(void)
{
mutex_lock(&sched_dynamic_mutex);
klp_override = false;
__sched_dynamic_update(preempt_dynamic_mode);
mutex_unlock(&sched_dynamic_mutex);
}
#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
static int __init setup_preempt_mode(char *str)
{
int mode = sched_dynamic_mode(str);
if (mode < 0) {
pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
return 0;
}
sched_dynamic_update(mode);
return 1;
}
__setup("preempt=", setup_preempt_mode);
static void __init preempt_dynamic_init(void)
{
if (preempt_dynamic_mode == preempt_dynamic_undefined) {
if (IS_ENABLED(CONFIG_PREEMPT_NONE)) {
sched_dynamic_update(preempt_dynamic_none);
} else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)) {
sched_dynamic_update(preempt_dynamic_voluntary);
} else {
/* Default static call setting, nothing to do */
WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT));
preempt_dynamic_mode = preempt_dynamic_full;
pr_info("Dynamic Preempt: full\n");
}
}
}
#define PREEMPT_MODEL_ACCESSOR(mode) \
bool preempt_model_##mode(void) \
{ \
WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
return preempt_dynamic_mode == preempt_dynamic_##mode; \
} \
EXPORT_SYMBOL_GPL(preempt_model_##mode)
PREEMPT_MODEL_ACCESSOR(none);
PREEMPT_MODEL_ACCESSOR(voluntary);
PREEMPT_MODEL_ACCESSOR(full);
#else /* !CONFIG_PREEMPT_DYNAMIC: */
static inline void preempt_dynamic_init(void) { }
#endif /* CONFIG_PREEMPT_DYNAMIC */
int io_schedule_prepare(void)
{
int old_iowait = current->in_iowait;
current->in_iowait = 1;
blk_flush_plug(current->plug, true);
return old_iowait;
}
void io_schedule_finish(int token)
{
current->in_iowait = token;
}
/*
* This task is about to go to sleep on IO. Increment rq->nr_iowait so
* that process accounting knows that this is a task in IO wait state.
*/
long __sched io_schedule_timeout(long timeout)
{
int token;
long ret;
token = io_schedule_prepare();
ret = schedule_timeout(timeout);
io_schedule_finish(token);
return ret;
}
EXPORT_SYMBOL(io_schedule_timeout);
void __sched io_schedule(void)
{
int token;
token = io_schedule_prepare();
schedule();
io_schedule_finish(token);
}
EXPORT_SYMBOL(io_schedule);
void sched_show_task(struct task_struct *p)
{
unsigned long free;
int ppid;
if (!try_get_task_stack(p))
return;
pr_info("task:%-15.15s state:%c", p->comm, task_state_to_char(p));
if (task_is_running(p))
pr_cont(" running task ");
free = stack_not_used(p);
ppid = 0;
rcu_read_lock();
if (pid_alive(p))
ppid = task_pid_nr(rcu_dereference(p->real_parent));
rcu_read_unlock();
pr_cont(" stack:%-5lu pid:%-5d tgid:%-5d ppid:%-6d flags:0x%08lx\n",
free, task_pid_nr(p), task_tgid_nr(p),
ppid, read_task_thread_flags(p));
print_worker_info(KERN_INFO, p);
print_stop_info(KERN_INFO, p);
print_scx_info(KERN_INFO, p);
show_stack(p, NULL, KERN_INFO);
put_task_stack(p);
}
EXPORT_SYMBOL_GPL(sched_show_task);
static inline bool
state_filter_match(unsigned long state_filter, struct task_struct *p)
{
unsigned int state = READ_ONCE(p->__state);
/* no filter, everything matches */
if (!state_filter)
return true;
/* filter, but doesn't match */
if (!(state & state_filter))
return false;
/*
* When looking for TASK_UNINTERRUPTIBLE skip TASK_IDLE (allows
* TASK_KILLABLE).
*/
if (state_filter == TASK_UNINTERRUPTIBLE && (state & TASK_NOLOAD))
return false;
return true;
}
void show_state_filter(unsigned int state_filter)
{
struct task_struct *g, *p;
rcu_read_lock();
for_each_process_thread(g, p) {
/*
* reset the NMI-timeout, listing all files on a slow
* console might take a lot of time:
* Also, reset softlockup watchdogs on all CPUs, because
* another CPU might be blocked waiting for us to process
* an IPI.
*/
touch_nmi_watchdog();
touch_all_softlockup_watchdogs();
if (state_filter_match(state_filter, p))
sched_show_task(p);
}
#ifdef CONFIG_SCHED_DEBUG
if (!state_filter)
sysrq_sched_debug_show();
#endif
rcu_read_unlock();
/*
* Only show locks if all tasks are dumped:
*/
if (!state_filter)
debug_show_all_locks();
}
/**
* init_idle - set up an idle thread for a given CPU
* @idle: task in question
* @cpu: CPU the idle task belongs to
*
* NOTE: this function does not set the idle thread's NEED_RESCHED
* flag, to make booting more robust.
*/
void __init init_idle(struct task_struct *idle, int cpu)
{
#ifdef CONFIG_SMP
struct affinity_context ac = (struct affinity_context) {
.new_mask = cpumask_of(cpu),
.flags = 0,
};
#endif
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
__sched_fork(0, idle);
raw_spin_lock_irqsave(&idle->pi_lock, flags);
raw_spin_rq_lock(rq);
idle->__state = TASK_RUNNING;
idle->se.exec_start = sched_clock();
/*
* PF_KTHREAD should already be set at this point; regardless, make it
* look like a proper per-CPU kthread.
*/
idle->flags |= PF_KTHREAD | PF_NO_SETAFFINITY;
kthread_set_per_cpu(idle, cpu);
#ifdef CONFIG_SMP
/*
* It's possible that init_idle() gets called multiple times on a task,
* in that case do_set_cpus_allowed() will not do the right thing.
*
* And since this is boot we can forgo the serialization.
*/
set_cpus_allowed_common(idle, &ac);
#endif
/*
* We're having a chicken and egg problem, even though we are
* holding rq->lock, the CPU isn't yet set to this CPU so the
* lockdep check in task_group() will fail.
*
* Similar case to sched_fork(). / Alternatively we could
* use task_rq_lock() here and obtain the other rq->lock.
*
* Silence PROVE_RCU
*/
rcu_read_lock();
__set_task_cpu(idle, cpu);
rcu_read_unlock();
rq->idle = idle;
rcu_assign_pointer(rq->curr, idle);
idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
idle->on_cpu = 1;
#endif
raw_spin_rq_unlock(rq);
raw_spin_unlock_irqrestore(&idle->pi_lock, flags);
/* Set the preempt count _outside_ the spinlocks! */
init_idle_preempt_count(idle, cpu);
/*
* The idle tasks have their own, simple scheduling class:
*/
idle->sched_class = &idle_sched_class;
ftrace_graph_init_idle_task(idle, cpu);
vtime_init_idle(idle, cpu);
#ifdef CONFIG_SMP
sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
#endif
}
#ifdef CONFIG_SMP
int cpuset_cpumask_can_shrink(const struct cpumask *cur,
const struct cpumask *trial)
{
int ret = 1;
if (cpumask_empty(cur))
return ret;
ret = dl_cpuset_cpumask_can_shrink(cur, trial);
return ret;
}
int task_can_attach(struct task_struct *p)
{
int ret = 0;
/*
* Kthreads which disallow setaffinity shouldn't be moved
* to a new cpuset; we don't want to change their CPU
* affinity and isolating such threads by their set of
* allowed nodes is unnecessary. Thus, cpusets are not
* applicable for such threads. This prevents checking for
* success of set_cpus_allowed_ptr() on all attached tasks
* before cpus_mask may be changed.
*/
if (p->flags & PF_NO_SETAFFINITY)
ret = -EINVAL;
return ret;
}
bool sched_smp_initialized __read_mostly;
#ifdef CONFIG_NUMA_BALANCING
/* Migrate current task p to target_cpu */
int migrate_task_to(struct task_struct *p, int target_cpu)
{
struct migration_arg arg = { p, target_cpu };
int curr_cpu = task_cpu(p);
if (curr_cpu == target_cpu)
return 0;
if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
return -EINVAL;
/* TODO: This is not properly updating schedstats */
trace_sched_move_numa(p, curr_cpu, target_cpu);
return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}
/*
* Requeue a task on a given node and accurately track the number of NUMA
* tasks on the runqueues
*/
void sched_setnuma(struct task_struct *p, int nid)
{
bool queued, running;
struct rq_flags rf;
struct rq *rq;
rq = task_rq_lock(p, &rf);
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE);
if (running)
put_prev_task(rq, p);
p->numa_preferred_nid = nid;
if (queued)
enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
if (running)
set_next_task(rq, p);
task_rq_unlock(rq, p, &rf);
}
#endif /* CONFIG_NUMA_BALANCING */
#ifdef CONFIG_HOTPLUG_CPU
/*
* Ensure that the idle task is using init_mm right before its CPU goes
* offline.
*/
void idle_task_exit(void)
{
struct mm_struct *mm = current->active_mm;
BUG_ON(cpu_online(smp_processor_id()));
BUG_ON(current != this_rq()->idle);
if (mm != &init_mm) {
switch_mm(mm, &init_mm, current);
finish_arch_post_lock_switch();
}
/* finish_cpu(), as ran on the BP, will clean up the active_mm state */
}
static int __balance_push_cpu_stop(void *arg)
{
struct task_struct *p = arg;
struct rq *rq = this_rq();
struct rq_flags rf;
int cpu;
raw_spin_lock_irq(&p->pi_lock);
rq_lock(rq, &rf);
update_rq_clock(rq);
if (task_rq(p) == rq && task_on_rq_queued(p)) {
cpu = select_fallback_rq(rq->cpu, p);
rq = __migrate_task(rq, &rf, p, cpu);
}
rq_unlock(rq, &rf);
raw_spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
return 0;
}
static DEFINE_PER_CPU(struct cpu_stop_work, push_work);
/*
* Ensure we only run per-cpu kthreads once the CPU goes !active.
*
* This is enabled below SCHED_AP_ACTIVE; when !cpu_active(), but only
* effective when the hotplug motion is down.
*/
static void balance_push(struct rq *rq)
{
struct task_struct *push_task = rq->curr;
lockdep_assert_rq_held(rq);
/*
* Ensure the thing is persistent until balance_push_set(.on = false);
*/
rq->balance_callback = &balance_push_callback;
/*
* Only active while going offline and when invoked on the outgoing
* CPU.
*/
if (!cpu_dying(rq->cpu) || rq != this_rq())
return;
/*
* Both the cpu-hotplug and stop task are in this case and are
* required to complete the hotplug process.
*/
if (kthread_is_per_cpu(push_task) ||
is_migration_disabled(push_task)) {
/*
* If this is the idle task on the outgoing CPU try to wake
* up the hotplug control thread which might wait for the
* last task to vanish. The rcuwait_active() check is
* accurate here because the waiter is pinned on this CPU
* and can't obviously be running in parallel.
*
* On RT kernels this also has to check whether there are
* pinned and scheduled out tasks on the runqueue. They
* need to leave the migrate disabled section first.
*/
if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
rcuwait_active(&rq->hotplug_wait)) {
raw_spin_rq_unlock(rq);
rcuwait_wake_up(&rq->hotplug_wait);
raw_spin_rq_lock(rq);
}
return;
}
get_task_struct(push_task);
/*
* Temporarily drop rq->lock such that we can wake-up the stop task.
* Both preemption and IRQs are still disabled.
*/
preempt_disable();
raw_spin_rq_unlock(rq);
stop_one_cpu_nowait(rq->cpu, __balance_push_cpu_stop, push_task,
this_cpu_ptr(&push_work));
preempt_enable();
/*
* At this point need_resched() is true and we'll take the loop in
* schedule(). The next pick is obviously going to be the stop task
* which kthread_is_per_cpu() and will push this task away.
*/
raw_spin_rq_lock(rq);
}
static void balance_push_set(int cpu, bool on)
{
struct rq *rq = cpu_rq(cpu);
struct rq_flags rf;
rq_lock_irqsave(rq, &rf);
if (on) {
WARN_ON_ONCE(rq->balance_callback);
rq->balance_callback = &balance_push_callback;
} else if (rq->balance_callback == &balance_push_callback) {
rq->balance_callback = NULL;
}
rq_unlock_irqrestore(rq, &rf);
}
/*
* Invoked from a CPUs hotplug control thread after the CPU has been marked
* inactive. All tasks which are not per CPU kernel threads are either
* pushed off this CPU now via balance_push() or placed on a different CPU
* during wakeup. Wait until the CPU is quiescent.
*/
static void balance_hotplug_wait(void)
{
struct rq *rq = this_rq();
rcuwait_wait_event(&rq->hotplug_wait,
rq->nr_running == 1 && !rq_has_pinned_tasks(rq),
TASK_UNINTERRUPTIBLE);
}
#else
static inline void balance_push(struct rq *rq)
{
}
static inline void balance_push_set(int cpu, bool on)
{
}
static inline void balance_hotplug_wait(void)
{
}
#endif /* CONFIG_HOTPLUG_CPU */
void set_rq_online(struct rq *rq)
{
if (!rq->online) {
const struct sched_class *class;
cpumask_set_cpu(rq->cpu, rq->rd->online);
rq->online = 1;
for_each_class(class) {
if (class->rq_online)
class->rq_online(rq);
}
}
}
void set_rq_offline(struct rq *rq)
{
if (rq->online) {
const struct sched_class *class;
update_rq_clock(rq);
for_each_class(class) {
if (class->rq_offline)
class->rq_offline(rq);
}
cpumask_clear_cpu(rq->cpu, rq->rd->online);
rq->online = 0;
}
}
static inline void sched_set_rq_online(struct rq *rq, int cpu)
{
struct rq_flags rf;
rq_lock_irqsave(rq, &rf);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
set_rq_online(rq);
}
rq_unlock_irqrestore(rq, &rf);
}
static inline void sched_set_rq_offline(struct rq *rq, int cpu)
{
struct rq_flags rf;
rq_lock_irqsave(rq, &rf);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
set_rq_offline(rq);
}
rq_unlock_irqrestore(rq, &rf);
}
/*
* used to mark begin/end of suspend/resume:
*/
static int num_cpus_frozen;
/*
* Update cpusets according to cpu_active mask. If cpusets are
* disabled, cpuset_update_active_cpus() becomes a simple wrapper
* around partition_sched_domains().
*
* If we come here as part of a suspend/resume, don't touch cpusets because we
* want to restore it back to its original state upon resume anyway.
*/
static void cpuset_cpu_active(void)
{
if (cpuhp_tasks_frozen) {
/*
* num_cpus_frozen tracks how many CPUs are involved in suspend
* resume sequence. As long as this is not the last online
* operation in the resume sequence, just build a single sched
* domain, ignoring cpusets.
*/
partition_sched_domains(1, NULL, NULL);
if (--num_cpus_frozen)
return;
/*
* This is the last CPU online operation. So fall through and
* restore the original sched domains by considering the
* cpuset configurations.
*/
cpuset_force_rebuild();
}
cpuset_update_active_cpus();
}
static int cpuset_cpu_inactive(unsigned int cpu)
{
if (!cpuhp_tasks_frozen) {
int ret = dl_bw_check_overflow(cpu);
if (ret)
return ret;
cpuset_update_active_cpus();
} else {
num_cpus_frozen++;
partition_sched_domains(1, NULL, NULL);
}
return 0;
}
static inline void sched_smt_present_inc(int cpu)
{
#ifdef CONFIG_SCHED_SMT
if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
static_branch_inc_cpuslocked(&sched_smt_present);
#endif
}
static inline void sched_smt_present_dec(int cpu)
{
#ifdef CONFIG_SCHED_SMT
if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
static_branch_dec_cpuslocked(&sched_smt_present);
#endif
}
int sched_cpu_activate(unsigned int cpu)
{
struct rq *rq = cpu_rq(cpu);
/*
* Clear the balance_push callback and prepare to schedule
* regular tasks.
*/
balance_push_set(cpu, false);
/*
* When going up, increment the number of cores with SMT present.
*/
sched_smt_present_inc(cpu);
set_cpu_active(cpu, true);
if (sched_smp_initialized) {
sched_update_numa(cpu, true);
sched_domains_numa_masks_set(cpu);
cpuset_cpu_active();
}
scx_rq_activate(rq);
/*
* Put the rq online, if not already. This happens:
*
* 1) In the early boot process, because we build the real domains
* after all CPUs have been brought up.
*
* 2) At runtime, if cpuset_cpu_active() fails to rebuild the
* domains.
*/
sched_set_rq_online(rq, cpu);
return 0;
}
int sched_cpu_deactivate(unsigned int cpu)
{
struct rq *rq = cpu_rq(cpu);
int ret;
/*
* Remove CPU from nohz.idle_cpus_mask to prevent participating in
* load balancing when not active
*/
nohz_balance_exit_idle(rq);
set_cpu_active(cpu, false);
/*
* From this point forward, this CPU will refuse to run any task that
* is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively
* push those tasks away until this gets cleared, see
* sched_cpu_dying().
*/
balance_push_set(cpu, true);
/*
* We've cleared cpu_active_mask / set balance_push, wait for all
* preempt-disabled and RCU users of this state to go away such that
* all new such users will observe it.
*
* Specifically, we rely on ttwu to no longer target this CPU, see
* ttwu_queue_cond() and is_cpu_allowed().
*
* Do sync before park smpboot threads to take care the RCU boost case.
*/
synchronize_rcu();
sched_set_rq_offline(rq, cpu);
scx_rq_deactivate(rq);
/*
* When going down, decrement the number of cores with SMT present.
*/
sched_smt_present_dec(cpu);
#ifdef CONFIG_SCHED_SMT
sched_core_cpu_deactivate(cpu);
#endif
if (!sched_smp_initialized)
return 0;
sched_update_numa(cpu, false);
ret = cpuset_cpu_inactive(cpu);
if (ret) {
sched_smt_present_inc(cpu);
sched_set_rq_online(rq, cpu);
balance_push_set(cpu, false);
set_cpu_active(cpu, true);
sched_update_numa(cpu, true);
return ret;
}
sched_domains_numa_masks_clear(cpu);
return 0;
}
static void sched_rq_cpu_starting(unsigned int cpu)
{
struct rq *rq = cpu_rq(cpu);
rq->calc_load_update = calc_load_update;
update_max_interval();
}
int sched_cpu_starting(unsigned int cpu)
{
sched_core_cpu_starting(cpu);
sched_rq_cpu_starting(cpu);
sched_tick_start(cpu);
return 0;
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* Invoked immediately before the stopper thread is invoked to bring the
* CPU down completely. At this point all per CPU kthreads except the
* hotplug thread (current) and the stopper thread (inactive) have been
* either parked or have been unbound from the outgoing CPU. Ensure that
* any of those which might be on the way out are gone.
*
* If after this point a bound task is being woken on this CPU then the
* responsible hotplug callback has failed to do it's job.
* sched_cpu_dying() will catch it with the appropriate fireworks.
*/
int sched_cpu_wait_empty(unsigned int cpu)
{
balance_hotplug_wait();
return 0;
}
/*
* Since this CPU is going 'away' for a while, fold any nr_active delta we
* might have. Called from the CPU stopper task after ensuring that the
* stopper is the last running task on the CPU, so nr_active count is
* stable. We need to take the tear-down thread which is calling this into
* account, so we hand in adjust = 1 to the load calculation.
*
* Also see the comment "Global load-average calculations".
*/
static void calc_load_migrate(struct rq *rq)
{
long delta = calc_load_fold_active(rq, 1);
if (delta)
atomic_long_add(delta, &calc_load_tasks);
}
static void dump_rq_tasks(struct rq *rq, const char *loglvl)
{
struct task_struct *g, *p;
int cpu = cpu_of(rq);
lockdep_assert_rq_held(rq);
printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
for_each_process_thread(g, p) {
if (task_cpu(p) != cpu)
continue;
if (!task_on_rq_queued(p))
continue;
printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
}
}
int sched_cpu_dying(unsigned int cpu)
{
struct rq *rq = cpu_rq(cpu);
struct rq_flags rf;
/* Handle pending wakeups and then migrate everything off */
sched_tick_stop(cpu);
rq_lock_irqsave(rq, &rf);
if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {
WARN(true, "Dying CPU not properly vacated!");
dump_rq_tasks(rq, KERN_WARNING);
}
rq_unlock_irqrestore(rq, &rf);
calc_load_migrate(rq);
update_max_interval();
hrtick_clear(rq);
sched_core_cpu_dying(cpu);
return 0;
}
#endif
void __init sched_init_smp(void)
{
sched_init_numa(NUMA_NO_NODE);
/*
* There's no userspace yet to cause hotplug operations; hence all the
* CPU masks are stable and all blatant races in the below code cannot
* happen.
*/
mutex_lock(&sched_domains_mutex);
sched_init_domains(cpu_active_mask);
mutex_unlock(&sched_domains_mutex);
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_DOMAIN)) < 0)
BUG();
current->flags &= ~PF_NO_SETAFFINITY;
sched_init_granularity();
init_sched_rt_class();
init_sched_dl_class();
sched_smp_initialized = true;
}
static int __init migration_init(void)
{
sched_cpu_starting(smp_processor_id());
return 0;
}
early_initcall(migration_init);
#else
void __init sched_init_smp(void)
{
sched_init_granularity();
}
#endif /* CONFIG_SMP */
int in_sched_functions(unsigned long addr)
{
return in_lock_functions(addr) ||
(addr >= (unsigned long)__sched_text_start
&& addr < (unsigned long)__sched_text_end);
}
#ifdef CONFIG_CGROUP_SCHED
/*
* Default task group.
* Every task in system belongs to this group at bootup.
*/
struct task_group root_task_group;
LIST_HEAD(task_groups);
/* Cacheline aligned slab cache for task_group */
static struct kmem_cache *task_group_cache __ro_after_init;
#endif
void __init sched_init(void)
{
unsigned long ptr = 0;
int i;
/* Make sure the linker didn't screw up */
#ifdef CONFIG_SMP
BUG_ON(!sched_class_above(&stop_sched_class, &dl_sched_class));
#endif
BUG_ON(!sched_class_above(&dl_sched_class, &rt_sched_class));
BUG_ON(!sched_class_above(&rt_sched_class, &fair_sched_class));
BUG_ON(!sched_class_above(&fair_sched_class, &idle_sched_class));
#ifdef CONFIG_SCHED_CLASS_EXT
BUG_ON(!sched_class_above(&fair_sched_class, &ext_sched_class));
BUG_ON(!sched_class_above(&ext_sched_class, &idle_sched_class));
#endif
wait_bit_init();
#ifdef CONFIG_FAIR_GROUP_SCHED
ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
#ifdef CONFIG_RT_GROUP_SCHED
ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
if (ptr) {
ptr = (unsigned long)kzalloc(ptr, GFP_NOWAIT);
#ifdef CONFIG_FAIR_GROUP_SCHED
root_task_group.se = (struct sched_entity **)ptr;
ptr += nr_cpu_ids * sizeof(void **);
root_task_group.cfs_rq = (struct cfs_rq **)ptr;
ptr += nr_cpu_ids * sizeof(void **);
root_task_group.shares = ROOT_TASK_GROUP_LOAD;
init_cfs_bandwidth(&root_task_group.cfs_bandwidth, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */
#ifdef CONFIG_EXT_GROUP_SCHED
root_task_group.scx_weight = CGROUP_WEIGHT_DFL;
#endif /* CONFIG_EXT_GROUP_SCHED */
#ifdef CONFIG_RT_GROUP_SCHED
root_task_group.rt_se = (struct sched_rt_entity **)ptr;
ptr += nr_cpu_ids * sizeof(void **);
root_task_group.rt_rq = (struct rt_rq **)ptr;
ptr += nr_cpu_ids * sizeof(void **);
#endif /* CONFIG_RT_GROUP_SCHED */
}
#ifdef CONFIG_SMP
init_defrootdomain();
#endif
#ifdef CONFIG_RT_GROUP_SCHED
init_rt_bandwidth(&root_task_group.rt_bandwidth,
global_rt_period(), global_rt_runtime());
#endif /* CONFIG_RT_GROUP_SCHED */
#ifdef CONFIG_CGROUP_SCHED
task_group_cache = KMEM_CACHE(task_group, 0);
list_add(&root_task_group.list, &task_groups);
INIT_LIST_HEAD(&root_task_group.children);
INIT_LIST_HEAD(&root_task_group.siblings);
autogroup_init(&init_task);
#endif /* CONFIG_CGROUP_SCHED */
for_each_possible_cpu(i) {
struct rq *rq;
rq = cpu_rq(i);
raw_spin_lock_init(&rq->__lock);
rq->nr_running = 0;
rq->calc_load_active = 0;
rq->calc_load_update = jiffies + LOAD_FREQ;
init_cfs_rq(&rq->cfs);
init_rt_rq(&rq->rt);
init_dl_rq(&rq->dl);
#ifdef CONFIG_FAIR_GROUP_SCHED
INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);
rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
/*
* How much CPU bandwidth does root_task_group get?
*
* In case of task-groups formed through the cgroup filesystem, it
* gets 100% of the CPU resources in the system. This overall
* system CPU resource is divided among the tasks of
* root_task_group and its child task-groups in a fair manner,
* based on each entity's (task or task-group's) weight
* (se->load.weight).
*
* In other words, if root_task_group has 10 tasks of weight
* 1024) and two child groups A0 and A1 (of weight 1024 each),
* then A0's share of the CPU resource is:
*
* A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
*
* We achieve this by letting root_task_group's tasks sit
* directly in rq->cfs (i.e root_task_group->se[] = NULL).
*/
init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */
#ifdef CONFIG_RT_GROUP_SCHED
/*
* This is required for init cpu because rt.c:__enable_runtime()
* starts working after scheduler_running, which is not the case
* yet.
*/
rq->rt.rt_runtime = global_rt_runtime();
init_tg_rt_entry(&root_task_group, &rq->rt, NULL, i, NULL);
#endif
#ifdef CONFIG_SMP
rq->sd = NULL;
rq->rd = NULL;
rq->cpu_capacity = SCHED_CAPACITY_SCALE;
rq->balance_callback = &balance_push_callback;
rq->active_balance = 0;
rq->next_balance = jiffies;
rq->push_cpu = 0;
rq->cpu = i;
rq->online = 0;
rq->idle_stamp = 0;
rq->avg_idle = 2*sysctl_sched_migration_cost;
rq->max_idle_balance_cost = sysctl_sched_migration_cost;
INIT_LIST_HEAD(&rq->cfs_tasks);
rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ_COMMON
rq->last_blocked_load_update_tick = jiffies;
atomic_set(&rq->nohz_flags, 0);
INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
#endif
#ifdef CONFIG_HOTPLUG_CPU
rcuwait_init(&rq->hotplug_wait);
#endif
#endif /* CONFIG_SMP */
hrtick_rq_init(rq);
atomic_set(&rq->nr_iowait, 0);
fair_server_init(rq);
#ifdef CONFIG_SCHED_CORE
rq->core = rq;
rq->core_pick = NULL;
rq->core_dl_server = NULL;
rq->core_enabled = 0;
rq->core_tree = RB_ROOT;
rq->core_forceidle_count = 0;
rq->core_forceidle_occupation = 0;
rq->core_forceidle_start = 0;
rq->core_cookie = 0UL;
#endif
zalloc_cpumask_var_node(&rq->scratch_mask, GFP_KERNEL, cpu_to_node(i));
}
set_load_weight(&init_task, false);
init_task.se.slice = sysctl_sched_base_slice,
/*
* The boot idle thread does lazy MMU switching as well:
*/
mmgrab_lazy_tlb(&init_mm);
enter_lazy_tlb(&init_mm, current);
/*
* The idle task doesn't need the kthread struct to function, but it
* is dressed up as a per-CPU kthread and thus needs to play the part
* if we want to avoid special-casing it in code that deals with per-CPU
* kthreads.
*/
WARN_ON(!set_kthread_struct(current));
/*
* Make us the idle thread. Technically, schedule() should not be
* called from this thread, however somewhere below it might be,
* but because we are the idle thread, we just pick up running again
* when this runqueue becomes "idle".
*/
init_idle(current, smp_processor_id());
calc_load_update = jiffies + LOAD_FREQ;
#ifdef CONFIG_SMP
idle_thread_set_boot_cpu();
balance_push_set(smp_processor_id(), false);
#endif
init_sched_fair_class();
init_sched_ext_class();
psi_init();
init_uclamp();
preempt_dynamic_init();
scheduler_running = 1;
}
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
void __might_sleep(const char *file, int line)
{
unsigned int state = get_current_state();
/*
* Blocking primitives will set (and therefore destroy) current->state,
* since we will exit with TASK_RUNNING make sure we enter with it,
* otherwise we will destroy state.
*/
WARN_ONCE(state != TASK_RUNNING && current->task_state_change,
"do not call blocking ops when !TASK_RUNNING; "
"state=%x set at [<%p>] %pS\n", state,
(void *)current->task_state_change,
(void *)current->task_state_change);
__might_resched(file, line, 0);
}
EXPORT_SYMBOL(__might_sleep);
static void print_preempt_disable_ip(int preempt_offset, unsigned long ip)
{
if (!IS_ENABLED(CONFIG_DEBUG_PREEMPT))
return;
if (preempt_count() == preempt_offset)
return;
pr_err("Preemption disabled at:");
print_ip_sym(KERN_ERR, ip);
}
static inline bool resched_offsets_ok(unsigned int offsets)
{
unsigned int nested = preempt_count();
nested += rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT;
return nested == offsets;
}
void __might_resched(const char *file, int line, unsigned int offsets)
{
/* Ratelimiting timestamp: */
static unsigned long prev_jiffy;
unsigned long preempt_disable_ip;
/* WARN_ON_ONCE() by default, no rate limit required: */
rcu_sleep_check();
if ((resched_offsets_ok(offsets) && !irqs_disabled() &&
!is_idle_task(current) && !current->non_block_count) ||
system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
oops_in_progress)
return;
if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
return;
prev_jiffy = jiffies;
/* Save this before calling printk(), since that will clobber it: */
preempt_disable_ip = get_preempt_disable_ip(current);
pr_err("BUG: sleeping function called from invalid context at %s:%d\n",
file, line);
pr_err("in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
in_atomic(), irqs_disabled(), current->non_block_count,
current->pid, current->comm);
pr_err("preempt_count: %x, expected: %x\n", preempt_count(),
offsets & MIGHT_RESCHED_PREEMPT_MASK);
if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
pr_err("RCU nest depth: %d, expected: %u\n",
rcu_preempt_depth(), offsets >> MIGHT_RESCHED_RCU_SHIFT);
}
if (task_stack_end_corrupted(current))
pr_emerg("Thread overran stack, or stack corrupted\n");
debug_show_held_locks(current);
if (irqs_disabled())
print_irqtrace_events(current);
print_preempt_disable_ip(offsets & MIGHT_RESCHED_PREEMPT_MASK,
preempt_disable_ip);
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL(__might_resched);
void __cant_sleep(const char *file, int line, int preempt_offset)
{
static unsigned long prev_jiffy;
if (irqs_disabled())
return;
if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
return;
if (preempt_count() > preempt_offset)
return;
if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
return;
prev_jiffy = jiffies;
printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
in_atomic(), irqs_disabled(),
current->pid, current->comm);
debug_show_held_locks(current);
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL_GPL(__cant_sleep);
#ifdef CONFIG_SMP
void __cant_migrate(const char *file, int line)
{
static unsigned long prev_jiffy;
if (irqs_disabled())
return;
if (is_migration_disabled(current))
return;
if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
return;
if (preempt_count() > 0)
return;
if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
return;
prev_jiffy = jiffies;
pr_err("BUG: assuming non migratable context at %s:%d\n", file, line);
pr_err("in_atomic(): %d, irqs_disabled(): %d, migration_disabled() %u pid: %d, name: %s\n",
in_atomic(), irqs_disabled(), is_migration_disabled(current),
current->pid, current->comm);
debug_show_held_locks(current);
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL_GPL(__cant_migrate);
#endif
#endif
#ifdef CONFIG_MAGIC_SYSRQ
void normalize_rt_tasks(void)
{
struct task_struct *g, *p;
struct sched_attr attr = {
.sched_policy = SCHED_NORMAL,
};
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
/*
* Only normalize user tasks:
*/
if (p->flags & PF_KTHREAD)
continue;
p->se.exec_start = 0;
schedstat_set(p->stats.wait_start, 0);
schedstat_set(p->stats.sleep_start, 0);
schedstat_set(p->stats.block_start, 0);
if (!rt_or_dl_task(p)) {
/*
* Renice negative nice level userspace
* tasks back to 0:
*/
if (task_nice(p) < 0)
set_user_nice(p, 0);
continue;
}
__sched_setscheduler(p, &attr, false, false);
}
read_unlock(&tasklist_lock);
}
#endif /* CONFIG_MAGIC_SYSRQ */
#if defined(CONFIG_KGDB_KDB)
/*
* These functions are only useful for KDB.
*
* They can only be called when the whole system has been
* stopped - every CPU needs to be quiescent, and no scheduling
* activity can take place. Using them for anything else would
* be a serious bug, and as a result, they aren't even visible
* under any other configuration.
*/
/**
* curr_task - return the current task for a given CPU.
* @cpu: the processor in question.
*
* ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
*
* Return: The current task for @cpu.
*/
struct task_struct *curr_task(int cpu)
{
return cpu_curr(cpu);
}
#endif /* defined(CONFIG_KGDB_KDB) */
#ifdef CONFIG_CGROUP_SCHED
/* task_group_lock serializes the addition/removal of task groups */
static DEFINE_SPINLOCK(task_group_lock);
static inline void alloc_uclamp_sched_group(struct task_group *tg,
struct task_group *parent)
{
#ifdef CONFIG_UCLAMP_TASK_GROUP
enum uclamp_id clamp_id;
for_each_clamp_id(clamp_id) {
uclamp_se_set(&tg->uclamp_req[clamp_id],
uclamp_none(clamp_id), false);
tg->uclamp[clamp_id] = parent->uclamp[clamp_id];
}
#endif
}
static void sched_free_group(struct task_group *tg)
{
free_fair_sched_group(tg);
free_rt_sched_group(tg);
autogroup_free(tg);
kmem_cache_free(task_group_cache, tg);
}
static void sched_free_group_rcu(struct rcu_head *rcu)
{
sched_free_group(container_of(rcu, struct task_group, rcu));
}
static void sched_unregister_group(struct task_group *tg)
{
unregister_fair_sched_group(tg);
unregister_rt_sched_group(tg);
/*
* We have to wait for yet another RCU grace period to expire, as
* print_cfs_stats() might run concurrently.
*/
call_rcu(&tg->rcu, sched_free_group_rcu);
}
/* allocate runqueue etc for a new task group */
struct task_group *sched_create_group(struct task_group *parent)
{
struct task_group *tg;
tg = kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO);
if (!tg)
return ERR_PTR(-ENOMEM);
if (!alloc_fair_sched_group(tg, parent))
goto err;
if (!alloc_rt_sched_group(tg, parent))
goto err;
scx_group_set_weight(tg, CGROUP_WEIGHT_DFL);
alloc_uclamp_sched_group(tg, parent);
return tg;
err:
sched_free_group(tg);
return ERR_PTR(-ENOMEM);
}
void sched_online_group(struct task_group *tg, struct task_group *parent)
{
unsigned long flags;
spin_lock_irqsave(&task_group_lock, flags);
list_add_rcu(&tg->list, &task_groups);
/* Root should already exist: */
WARN_ON(!parent);
tg->parent = parent;
INIT_LIST_HEAD(&tg->children);
list_add_rcu(&tg->siblings, &parent->children);
spin_unlock_irqrestore(&task_group_lock, flags);
online_fair_sched_group(tg);
}
/* RCU callback to free various structures associated with a task group */
static void sched_unregister_group_rcu(struct rcu_head *rhp)
{
/* Now it should be safe to free those cfs_rqs: */
sched_unregister_group(container_of(rhp, struct task_group, rcu));
}
void sched_destroy_group(struct task_group *tg)
{
/* Wait for possible concurrent references to cfs_rqs complete: */
call_rcu(&tg->rcu, sched_unregister_group_rcu);
}
void sched_release_group(struct task_group *tg)
{
unsigned long flags;
/*
* Unlink first, to avoid walk_tg_tree_from() from finding us (via
* sched_cfs_period_timer()).
*
* For this to be effective, we have to wait for all pending users of
* this task group to leave their RCU critical section to ensure no new
* user will see our dying task group any more. Specifically ensure
* that tg_unthrottle_up() won't add decayed cfs_rq's to it.
*
* We therefore defer calling unregister_fair_sched_group() to
* sched_unregister_group() which is guarantied to get called only after the
* current RCU grace period has expired.
*/
spin_lock_irqsave(&task_group_lock, flags);
list_del_rcu(&tg->list);
list_del_rcu(&tg->siblings);
spin_unlock_irqrestore(&task_group_lock, flags);
}
static struct task_group *sched_get_task_group(struct task_struct *tsk)
{
struct task_group *tg;
/*
* All callers are synchronized by task_rq_lock(); we do not use RCU
* which is pointless here. Thus, we pass "true" to task_css_check()
* to prevent lockdep warnings.
*/
tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
struct task_group, css);
tg = autogroup_task_group(tsk, tg);
return tg;
}
static void sched_change_group(struct task_struct *tsk, struct task_group *group)
{
tsk->sched_task_group = group;
#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->task_change_group)
tsk->sched_class->task_change_group(tsk);
else
#endif
set_task_rq(tsk, task_cpu(tsk));
}
/*
* Change task's runqueue when it moves between groups.
*
* The caller of this function should have put the task in its new group by
* now. This function just updates tsk->se.cfs_rq and tsk->se.parent to reflect
* its new group.
*/
void sched_move_task(struct task_struct *tsk)
{
int queued, running, queue_flags =
DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
struct task_group *group;
struct rq *rq;
CLASS(task_rq_lock, rq_guard)(tsk);
rq = rq_guard.rq;
/*
* Esp. with SCHED_AUTOGROUP enabled it is possible to get superfluous
* group changes.
*/
group = sched_get_task_group(tsk);
if (group == tsk->sched_task_group)
return;
update_rq_clock(rq);
running = task_current(rq, tsk);
queued = task_on_rq_queued(tsk);
if (queued)
dequeue_task(rq, tsk, queue_flags);
if (running)
put_prev_task(rq, tsk);
sched_change_group(tsk, group);
scx_move_task(tsk);
if (queued)
enqueue_task(rq, tsk, queue_flags);
if (running) {
set_next_task(rq, tsk);
/*
* After changing group, the running task may have joined a
* throttled one but it's still the running task. Trigger a
* resched to make sure that task can still run.
*/
resched_curr(rq);
}
}
static struct cgroup_subsys_state *
cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
struct task_group *parent = css_tg(parent_css);
struct task_group *tg;
if (!parent) {
/* This is early initialization for the top cgroup */
return &root_task_group.css;
}
tg = sched_create_group(parent);
if (IS_ERR(tg))
return ERR_PTR(-ENOMEM);
return &tg->css;
}
/* Expose task group only after completing cgroup initialization */
static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
struct task_group *parent = css_tg(css->parent);
int ret;
ret = scx_tg_online(tg);
if (ret)
return ret;
if (parent)
sched_online_group(tg, parent);
#ifdef CONFIG_UCLAMP_TASK_GROUP
/* Propagate the effective uclamp value for the new group */
guard(mutex)(&uclamp_mutex);
guard(rcu)();
cpu_util_update_eff(css);
#endif
return 0;
}
static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
scx_tg_offline(tg);
}
static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
sched_release_group(tg);
}
static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
/*
* Relies on the RCU grace period between css_released() and this.
*/
sched_unregister_group(tg);
}
static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
{
#ifdef CONFIG_RT_GROUP_SCHED
struct task_struct *task;
struct cgroup_subsys_state *css;
cgroup_taskset_for_each(task, css, tset) {
if (!sched_rt_can_attach(css_tg(css), task))
return -EINVAL;
}
#endif
return scx_cgroup_can_attach(tset);
}
static void cpu_cgroup_attach(struct cgroup_taskset *tset)
{
struct task_struct *task;
struct cgroup_subsys_state *css;
cgroup_taskset_for_each(task, css, tset)
sched_move_task(task);
scx_cgroup_finish_attach();
}
static void cpu_cgroup_cancel_attach(struct cgroup_taskset *tset)
{
scx_cgroup_cancel_attach(tset);
}
#ifdef CONFIG_UCLAMP_TASK_GROUP
static void cpu_util_update_eff(struct cgroup_subsys_state *css)
{
struct cgroup_subsys_state *top_css = css;
struct uclamp_se *uc_parent = NULL;
struct uclamp_se *uc_se = NULL;
unsigned int eff[UCLAMP_CNT];
enum uclamp_id clamp_id;
unsigned int clamps;
lockdep_assert_held(&uclamp_mutex);
SCHED_WARN_ON(!rcu_read_lock_held());
css_for_each_descendant_pre(css, top_css) {
uc_parent = css_tg(css)->parent
? css_tg(css)->parent->uclamp : NULL;
for_each_clamp_id(clamp_id) {
/* Assume effective clamps matches requested clamps */
eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
/* Cap effective clamps with parent's effective clamps */
if (uc_parent &&
eff[clamp_id] > uc_parent[clamp_id].value) {
eff[clamp_id] = uc_parent[clamp_id].value;
}
}
/* Ensure protection is always capped by limit */
eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
/* Propagate most restrictive effective clamps */
clamps = 0x0;
uc_se = css_tg(css)->uclamp;
for_each_clamp_id(clamp_id) {
if (eff[clamp_id] == uc_se[clamp_id].value)
continue;
uc_se[clamp_id].value = eff[clamp_id];
uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
clamps |= (0x1 << clamp_id);
}
if (!clamps) {
css = css_rightmost_descendant(css);
continue;
}
/* Immediately update descendants RUNNABLE tasks */
uclamp_update_active_tasks(css);
}
}
/*
* Integer 10^N with a given N exponent by casting to integer the literal "1eN"
* C expression. Since there is no way to convert a macro argument (N) into a
* character constant, use two levels of macros.
*/
#define _POW10(exp) ((unsigned int)1e##exp)
#define POW10(exp) _POW10(exp)
struct uclamp_request {
#define UCLAMP_PERCENT_SHIFT 2
#define UCLAMP_PERCENT_SCALE (100 * POW10(UCLAMP_PERCENT_SHIFT))
s64 percent;
u64 util;
int ret;
};
static inline struct uclamp_request
capacity_from_percent(char *buf)
{
struct uclamp_request req = {
.percent = UCLAMP_PERCENT_SCALE,
.util = SCHED_CAPACITY_SCALE,
.ret = 0,
};
buf = strim(buf);
if (strcmp(buf, "max")) {
req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
&req.percent);
if (req.ret)
return req;
if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
req.ret = -ERANGE;
return req;
}
req.util = req.percent << SCHED_CAPACITY_SHIFT;
req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
}
return req;
}
static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off,
enum uclamp_id clamp_id)
{
struct uclamp_request req;
struct task_group *tg;
req = capacity_from_percent(buf);
if (req.ret)
return req.ret;
static_branch_enable(&sched_uclamp_used);
guard(mutex)(&uclamp_mutex);
guard(rcu)();
tg = css_tg(of_css(of));
if (tg->uclamp_req[clamp_id].value != req.util)
uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);
/*
* Because of not recoverable conversion rounding we keep track of the
* exact requested value
*/
tg->uclamp_pct[clamp_id] = req.percent;
/* Update effective clamps to track the most restrictive value */
cpu_util_update_eff(of_css(of));
return nbytes;
}
static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
char *buf, size_t nbytes,
loff_t off)
{
return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MIN);
}
static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
char *buf, size_t nbytes,
loff_t off)
{
return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MAX);
}
static inline void cpu_uclamp_print(struct seq_file *sf,
enum uclamp_id clamp_id)
{
struct task_group *tg;
u64 util_clamp;
u64 percent;
u32 rem;
scoped_guard (rcu) {
tg = css_tg(seq_css(sf));
util_clamp = tg->uclamp_req[clamp_id].value;
}
if (util_clamp == SCHED_CAPACITY_SCALE) {
seq_puts(sf, "max\n");
return;
}
percent = tg->uclamp_pct[clamp_id];
percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem);
seq_printf(sf, "%llu.%0*u\n", percent, UCLAMP_PERCENT_SHIFT, rem);
}
static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
{
cpu_uclamp_print(sf, UCLAMP_MIN);
return 0;
}
static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
{
cpu_uclamp_print(sf, UCLAMP_MAX);
return 0;
}
#endif /* CONFIG_UCLAMP_TASK_GROUP */
#ifdef CONFIG_GROUP_SCHED_WEIGHT
static unsigned long tg_weight(struct task_group *tg)
{
#ifdef CONFIG_FAIR_GROUP_SCHED
return scale_load_down(tg->shares);
#else
return sched_weight_from_cgroup(tg->scx_weight);
#endif
}
static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
struct cftype *cftype, u64 shareval)
{
int ret;
if (shareval > scale_load_down(ULONG_MAX))
shareval = MAX_SHARES;
ret = sched_group_set_shares(css_tg(css), scale_load(shareval));
if (!ret)
scx_group_set_weight(css_tg(css),
sched_weight_to_cgroup(shareval));
return ret;
}
static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return tg_weight(css_tg(css));
}
#endif /* CONFIG_GROUP_SCHED_WEIGHT */
#ifdef CONFIG_CFS_BANDWIDTH
static DEFINE_MUTEX(cfs_constraints_mutex);
const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */
/* More than 203 days if BW_SHIFT equals 20. */
static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC;
static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
u64 burst)
{
int i, ret = 0, runtime_enabled, runtime_was_enabled;
struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
if (tg == &root_task_group)
return -EINVAL;
/*
* Ensure we have at some amount of bandwidth every period. This is
* to prevent reaching a state of large arrears when throttled via
* entity_tick() resulting in prolonged exit starvation.
*/
if (quota < min_cfs_quota_period || period < min_cfs_quota_period)
return -EINVAL;
/*
* Likewise, bound things on the other side by preventing insane quota
* periods. This also allows us to normalize in computing quota
* feasibility.
*/
if (period > max_cfs_quota_period)
return -EINVAL;
/*
* Bound quota to defend quota against overflow during bandwidth shift.
*/
if (quota != RUNTIME_INF && quota > max_cfs_runtime)
return -EINVAL;
if (quota != RUNTIME_INF && (burst > quota ||
burst + quota > max_cfs_runtime))
return -EINVAL;
/*
* Prevent race between setting of cfs_rq->runtime_enabled and
* unthrottle_offline_cfs_rqs().
*/
guard(cpus_read_lock)();
guard(mutex)(&cfs_constraints_mutex);
ret = __cfs_schedulable(tg, period, quota);
if (ret)
return ret;
runtime_enabled = quota != RUNTIME_INF;
runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
/*
* If we need to toggle cfs_bandwidth_used, off->on must occur
* before making related changes, and on->off must occur afterwards
*/
if (runtime_enabled && !runtime_was_enabled)
cfs_bandwidth_usage_inc();
scoped_guard (raw_spinlock_irq, &cfs_b->lock) {
cfs_b->period = ns_to_ktime(period);
cfs_b->quota = quota;
cfs_b->burst = burst;
__refill_cfs_bandwidth_runtime(cfs_b);
/*
* Restart the period timer (if active) to handle new
* period expiry:
*/
if (runtime_enabled)
start_cfs_bandwidth(cfs_b);
}
for_each_online_cpu(i) {
struct cfs_rq *cfs_rq = tg->cfs_rq[i];
struct rq *rq = cfs_rq->rq;
guard(rq_lock_irq)(rq);
cfs_rq->runtime_enabled = runtime_enabled;
cfs_rq->runtime_remaining = 0;
if (cfs_rq->throttled)
unthrottle_cfs_rq(cfs_rq);
}
if (runtime_was_enabled && !runtime_enabled)
cfs_bandwidth_usage_dec();
return 0;
}
static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
{
u64 quota, period, burst;
period = ktime_to_ns(tg->cfs_bandwidth.period);
burst = tg->cfs_bandwidth.burst;
if (cfs_quota_us < 0)
quota = RUNTIME_INF;
else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
quota = (u64)cfs_quota_us * NSEC_PER_USEC;
else
return -EINVAL;
return tg_set_cfs_bandwidth(tg, period, quota, burst);
}
static long tg_get_cfs_quota(struct task_group *tg)
{
u64 quota_us;
if (tg->cfs_bandwidth.quota == RUNTIME_INF)
return -1;
quota_us = tg->cfs_bandwidth.quota;
do_div(quota_us, NSEC_PER_USEC);
return quota_us;
}
static int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
{
u64 quota, period, burst;
if ((u64)cfs_period_us > U64_MAX / NSEC_PER_USEC)
return -EINVAL;
period = (u64)cfs_period_us * NSEC_PER_USEC;
quota = tg->cfs_bandwidth.quota;
burst = tg->cfs_bandwidth.burst;
return tg_set_cfs_bandwidth(tg, period, quota, burst);
}
static long tg_get_cfs_period(struct task_group *tg)
{
u64 cfs_period_us;
cfs_period_us = ktime_to_ns(tg->cfs_bandwidth.period);
do_div(cfs_period_us, NSEC_PER_USEC);
return cfs_period_us;
}
static int tg_set_cfs_burst(struct task_group *tg, long cfs_burst_us)
{
u64 quota, period, burst;
if ((u64)cfs_burst_us > U64_MAX / NSEC_PER_USEC)
return -EINVAL;
burst = (u64)cfs_burst_us * NSEC_PER_USEC;
period = ktime_to_ns(tg->cfs_bandwidth.period);
quota = tg->cfs_bandwidth.quota;
return tg_set_cfs_bandwidth(tg, period, quota, burst);
}
static long tg_get_cfs_burst(struct task_group *tg)
{
u64 burst_us;
burst_us = tg->cfs_bandwidth.burst;
do_div(burst_us, NSEC_PER_USEC);
return burst_us;
}
static s64 cpu_cfs_quota_read_s64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return tg_get_cfs_quota(css_tg(css));
}
static int cpu_cfs_quota_write_s64(struct cgroup_subsys_state *css,
struct cftype *cftype, s64 cfs_quota_us)
{
return tg_set_cfs_quota(css_tg(css), cfs_quota_us);
}
static u64 cpu_cfs_period_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return tg_get_cfs_period(css_tg(css));
}
static int cpu_cfs_period_write_u64(struct cgroup_subsys_state *css,
struct cftype *cftype, u64 cfs_period_us)
{
return tg_set_cfs_period(css_tg(css), cfs_period_us);
}
static u64 cpu_cfs_burst_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return tg_get_cfs_burst(css_tg(css));
}
static int cpu_cfs_burst_write_u64(struct cgroup_subsys_state *css,
struct cftype *cftype, u64 cfs_burst_us)
{
return tg_set_cfs_burst(css_tg(css), cfs_burst_us);
}
struct cfs_schedulable_data {
struct task_group *tg;
u64 period, quota;
};
/*
* normalize group quota/period to be quota/max_period
* note: units are usecs
*/
static u64 normalize_cfs_quota(struct task_group *tg,
struct cfs_schedulable_data *d)
{
u64 quota, period;
if (tg == d->tg) {
period = d->period;
quota = d->quota;
} else {
period = tg_get_cfs_period(tg);
quota = tg_get_cfs_quota(tg);
}
/* note: these should typically be equivalent */
if (quota == RUNTIME_INF || quota == -1)
return RUNTIME_INF;
return to_ratio(period, quota);
}
static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
{
struct cfs_schedulable_data *d = data;
struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
s64 quota = 0, parent_quota = -1;
if (!tg->parent) {
quota = RUNTIME_INF;
} else {
struct cfs_bandwidth *parent_b = &tg->parent->cfs_bandwidth;
quota = normalize_cfs_quota(tg, d);
parent_quota = parent_b->hierarchical_quota;
/*
* Ensure max(child_quota) <= parent_quota. On cgroup2,
* always take the non-RUNTIME_INF min. On cgroup1, only
* inherit when no limit is set. In both cases this is used
* by the scheduler to determine if a given CFS task has a
* bandwidth constraint at some higher level.
*/
if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
if (quota == RUNTIME_INF)
quota = parent_quota;
else if (parent_quota != RUNTIME_INF)
quota = min(quota, parent_quota);
} else {
if (quota == RUNTIME_INF)
quota = parent_quota;
else if (parent_quota != RUNTIME_INF && quota > parent_quota)
return -EINVAL;
}
}
cfs_b->hierarchical_quota = quota;
return 0;
}
static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
{
struct cfs_schedulable_data data = {
.tg = tg,
.period = period,
.quota = quota,
};
if (quota != RUNTIME_INF) {
do_div(data.period, NSEC_PER_USEC);
do_div(data.quota, NSEC_PER_USEC);
}
guard(rcu)();
return walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
}
static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
{
struct task_group *tg = css_tg(seq_css(sf));
struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
seq_printf(sf, "nr_periods %d\n", cfs_b->nr_periods);
seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);
if (schedstat_enabled() && tg != &root_task_group) {
struct sched_statistics *stats;
u64 ws = 0;
int i;
for_each_possible_cpu(i) {
stats = __schedstats_from_se(tg->se[i]);
ws += schedstat_val(stats->wait_sum);
}
seq_printf(sf, "wait_sum %llu\n", ws);
}
seq_printf(sf, "nr_bursts %d\n", cfs_b->nr_burst);
seq_printf(sf, "burst_time %llu\n", cfs_b->burst_time);
return 0;
}
static u64 throttled_time_self(struct task_group *tg)
{
int i;
u64 total = 0;
for_each_possible_cpu(i) {
total += READ_ONCE(tg->cfs_rq[i]->throttled_clock_self_time);
}
return total;
}
static int cpu_cfs_local_stat_show(struct seq_file *sf, void *v)
{
struct task_group *tg = css_tg(seq_css(sf));
seq_printf(sf, "throttled_time %llu\n", throttled_time_self(tg));
return 0;
}
#endif /* CONFIG_CFS_BANDWIDTH */
#ifdef CONFIG_RT_GROUP_SCHED
static int cpu_rt_runtime_write(struct cgroup_subsys_state *css,
struct cftype *cft, s64 val)
{
return sched_group_set_rt_runtime(css_tg(css), val);
}
static s64 cpu_rt_runtime_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return sched_group_rt_runtime(css_tg(css));
}
static int cpu_rt_period_write_uint(struct cgroup_subsys_state *css,
struct cftype *cftype, u64 rt_period_us)
{
return sched_group_set_rt_period(css_tg(css), rt_period_us);
}
static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return sched_group_rt_period(css_tg(css));
}
#endif /* CONFIG_RT_GROUP_SCHED */
#ifdef CONFIG_GROUP_SCHED_WEIGHT
static s64 cpu_idle_read_s64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return css_tg(css)->idle;
}
static int cpu_idle_write_s64(struct cgroup_subsys_state *css,
struct cftype *cft, s64 idle)
{
int ret;
ret = sched_group_set_idle(css_tg(css), idle);
if (!ret)
scx_group_set_idle(css_tg(css), idle);
return ret;
}
#endif
static struct cftype cpu_legacy_files[] = {
#ifdef CONFIG_GROUP_SCHED_WEIGHT
{
.name = "shares",
.read_u64 = cpu_shares_read_u64,
.write_u64 = cpu_shares_write_u64,
},
{
.name = "idle",
.read_s64 = cpu_idle_read_s64,
.write_s64 = cpu_idle_write_s64,
},
#endif
#ifdef CONFIG_CFS_BANDWIDTH
{
.name = "cfs_quota_us",
.read_s64 = cpu_cfs_quota_read_s64,
.write_s64 = cpu_cfs_quota_write_s64,
},
{
.name = "cfs_period_us",
.read_u64 = cpu_cfs_period_read_u64,
.write_u64 = cpu_cfs_period_write_u64,
},
{
.name = "cfs_burst_us",
.read_u64 = cpu_cfs_burst_read_u64,
.write_u64 = cpu_cfs_burst_write_u64,
},
{
.name = "stat",
.seq_show = cpu_cfs_stat_show,
},
{
.name = "stat.local",
.seq_show = cpu_cfs_local_stat_show,
},
#endif
#ifdef CONFIG_RT_GROUP_SCHED
{
.name = "rt_runtime_us",
.read_s64 = cpu_rt_runtime_read,
.write_s64 = cpu_rt_runtime_write,
},
{
.name = "rt_period_us",
.read_u64 = cpu_rt_period_read_uint,
.write_u64 = cpu_rt_period_write_uint,
},
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
{
.name = "uclamp.min",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_uclamp_min_show,
.write = cpu_uclamp_min_write,
},
{
.name = "uclamp.max",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_uclamp_max_show,
.write = cpu_uclamp_max_write,
},
#endif
{ } /* Terminate */
};
static int cpu_extra_stat_show(struct seq_file *sf,
struct cgroup_subsys_state *css)
{
#ifdef CONFIG_CFS_BANDWIDTH
{
struct task_group *tg = css_tg(css);
struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
u64 throttled_usec, burst_usec;
throttled_usec = cfs_b->throttled_time;
do_div(throttled_usec, NSEC_PER_USEC);
burst_usec = cfs_b->burst_time;
do_div(burst_usec, NSEC_PER_USEC);
seq_printf(sf, "nr_periods %d\n"
"nr_throttled %d\n"
"throttled_usec %llu\n"
"nr_bursts %d\n"
"burst_usec %llu\n",
cfs_b->nr_periods, cfs_b->nr_throttled,
throttled_usec, cfs_b->nr_burst, burst_usec);
}
#endif
return 0;
}
static int cpu_local_stat_show(struct seq_file *sf,
struct cgroup_subsys_state *css)
{
#ifdef CONFIG_CFS_BANDWIDTH
{
struct task_group *tg = css_tg(css);
u64 throttled_self_usec;
throttled_self_usec = throttled_time_self(tg);
do_div(throttled_self_usec, NSEC_PER_USEC);
seq_printf(sf, "throttled_usec %llu\n",
throttled_self_usec);
}
#endif
return 0;
}
#ifdef CONFIG_GROUP_SCHED_WEIGHT
static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
return sched_weight_to_cgroup(tg_weight(css_tg(css)));
}
static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
struct cftype *cft, u64 cgrp_weight)
{
unsigned long weight;
int ret;
if (cgrp_weight < CGROUP_WEIGHT_MIN || cgrp_weight > CGROUP_WEIGHT_MAX)
return -ERANGE;
weight = sched_weight_from_cgroup(cgrp_weight);
ret = sched_group_set_shares(css_tg(css), scale_load(weight));
if (!ret)
scx_group_set_weight(css_tg(css), cgrp_weight);
return ret;
}
static s64 cpu_weight_nice_read_s64(struct cgroup_subsys_state *css,
struct cftype *cft)
{
unsigned long weight = tg_weight(css_tg(css));
int last_delta = INT_MAX;
int prio, delta;
/* find the closest nice value to the current weight */
for (prio = 0; prio < ARRAY_SIZE(sched_prio_to_weight); prio++) {
delta = abs(sched_prio_to_weight[prio] - weight);
if (delta >= last_delta)
break;
last_delta = delta;
}
return PRIO_TO_NICE(prio - 1 + MAX_RT_PRIO);
}
static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
struct cftype *cft, s64 nice)
{
unsigned long weight;
int idx, ret;
if (nice < MIN_NICE || nice > MAX_NICE)
return -ERANGE;
idx = NICE_TO_PRIO(nice) - MAX_RT_PRIO;
idx = array_index_nospec(idx, 40);
weight = sched_prio_to_weight[idx];
ret = sched_group_set_shares(css_tg(css), scale_load(weight));
if (!ret)
scx_group_set_weight(css_tg(css),
sched_weight_to_cgroup(weight));
return ret;
}
#endif /* CONFIG_GROUP_SCHED_WEIGHT */
static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
long period, long quota)
{
if (quota < 0)
seq_puts(sf, "max");
else
seq_printf(sf, "%ld", quota);
seq_printf(sf, " %ld\n", period);
}
/* caller should put the current value in *@periodp before calling */
static int __maybe_unused cpu_period_quota_parse(char *buf,
u64 *periodp, u64 *quotap)
{
char tok[21]; /* U64_MAX */
if (sscanf(buf, "%20s %llu", tok, periodp) < 1)
return -EINVAL;
*periodp *= NSEC_PER_USEC;
if (sscanf(tok, "%llu", quotap))
*quotap *= NSEC_PER_USEC;
else if (!strcmp(tok, "max"))
*quotap = RUNTIME_INF;
else
return -EINVAL;
return 0;
}
#ifdef CONFIG_CFS_BANDWIDTH
static int cpu_max_show(struct seq_file *sf, void *v)
{
struct task_group *tg = css_tg(seq_css(sf));
cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
return 0;
}
static ssize_t cpu_max_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
struct task_group *tg = css_tg(of_css(of));
u64 period = tg_get_cfs_period(tg);
u64 burst = tg->cfs_bandwidth.burst;
u64 quota;
int ret;
ret = cpu_period_quota_parse(buf, &period, "a);
if (!ret)
ret = tg_set_cfs_bandwidth(tg, period, quota, burst);
return ret ?: nbytes;
}
#endif
static struct cftype cpu_files[] = {
#ifdef CONFIG_GROUP_SCHED_WEIGHT
{
.name = "weight",
.flags = CFTYPE_NOT_ON_ROOT,
.read_u64 = cpu_weight_read_u64,
.write_u64 = cpu_weight_write_u64,
},
{
.name = "weight.nice",
.flags = CFTYPE_NOT_ON_ROOT,
.read_s64 = cpu_weight_nice_read_s64,
.write_s64 = cpu_weight_nice_write_s64,
},
{
.name = "idle",
.flags = CFTYPE_NOT_ON_ROOT,
.read_s64 = cpu_idle_read_s64,
.write_s64 = cpu_idle_write_s64,
},
#endif
#ifdef CONFIG_CFS_BANDWIDTH
{
.name = "max",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_max_show,
.write = cpu_max_write,
},
{
.name = "max.burst",
.flags = CFTYPE_NOT_ON_ROOT,
.read_u64 = cpu_cfs_burst_read_u64,
.write_u64 = cpu_cfs_burst_write_u64,
},
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
{
.name = "uclamp.min",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_uclamp_min_show,
.write = cpu_uclamp_min_write,
},
{
.name = "uclamp.max",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_uclamp_max_show,
.write = cpu_uclamp_max_write,
},
#endif
{ } /* terminate */
};
struct cgroup_subsys cpu_cgrp_subsys = {
.css_alloc = cpu_cgroup_css_alloc,
.css_online = cpu_cgroup_css_online,
.css_offline = cpu_cgroup_css_offline,
.css_released = cpu_cgroup_css_released,
.css_free = cpu_cgroup_css_free,
.css_extra_stat_show = cpu_extra_stat_show,
.css_local_stat_show = cpu_local_stat_show,
.can_attach = cpu_cgroup_can_attach,
.attach = cpu_cgroup_attach,
.cancel_attach = cpu_cgroup_cancel_attach,
.legacy_cftypes = cpu_legacy_files,
.dfl_cftypes = cpu_files,
.early_init = true,
.threaded = true,
};
#endif /* CONFIG_CGROUP_SCHED */
void dump_cpu_task(int cpu)
{
if (in_hardirq() && cpu == smp_processor_id()) {
struct pt_regs *regs;
regs = get_irq_regs();
if (regs) {
show_regs(regs);
return;
}
}
if (trigger_single_cpu_backtrace(cpu))
return;
pr_info("Task dump for CPU %d:\n", cpu);
sched_show_task(cpu_curr(cpu));
}
/*
* Nice levels are multiplicative, with a gentle 10% change for every
* nice level changed. I.e. when a CPU-bound task goes from nice 0 to
* nice 1, it will get ~10% less CPU time than another CPU-bound task
* that remained on nice 0.
*
* The "10% effect" is relative and cumulative: from _any_ nice level,
* if you go up 1 level, it's -10% CPU usage, if you go down 1 level
* it's +10% CPU usage. (to achieve that we use a multiplier of 1.25.
* If a task goes up by ~10% and another task goes down by ~10% then
* the relative distance between them is ~25%.)
*/
const int sched_prio_to_weight[40] = {
/* -20 */ 88761, 71755, 56483, 46273, 36291,
/* -15 */ 29154, 23254, 18705, 14949, 11916,
/* -10 */ 9548, 7620, 6100, 4904, 3906,
/* -5 */ 3121, 2501, 1991, 1586, 1277,
/* 0 */ 1024, 820, 655, 526, 423,
/* 5 */ 335, 272, 215, 172, 137,
/* 10 */ 110, 87, 70, 56, 45,
/* 15 */ 36, 29, 23, 18, 15,
};
/*
* Inverse (2^32/x) values of the sched_prio_to_weight[] array, pre-calculated.
*
* In cases where the weight does not change often, we can use the
* pre-calculated inverse to speed up arithmetics by turning divisions
* into multiplications:
*/
const u32 sched_prio_to_wmult[40] = {
/* -20 */ 48388, 59856, 76040, 92818, 118348,
/* -15 */ 147320, 184698, 229616, 287308, 360437,
/* -10 */ 449829, 563644, 704093, 875809, 1099582,
/* -5 */ 1376151, 1717300, 2157191, 2708050, 3363326,
/* 0 */ 4194304, 5237765, 6557202, 8165337, 10153587,
/* 5 */ 12820798, 15790321, 19976592, 24970740, 31350126,
/* 10 */ 39045157, 49367440, 61356676, 76695844, 95443717,
/* 15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
};
void call_trace_sched_update_nr_running(struct rq *rq, int count)
{
trace_sched_update_nr_running_tp(rq, count);
}
#ifdef CONFIG_SCHED_MM_CID
/*
* @cid_lock: Guarantee forward-progress of cid allocation.
*
* Concurrency ID allocation within a bitmap is mostly lock-free. The cid_lock
* is only used when contention is detected by the lock-free allocation so
* forward progress can be guaranteed.
*/
DEFINE_RAW_SPINLOCK(cid_lock);
/*
* @use_cid_lock: Select cid allocation behavior: lock-free vs spinlock.
*
* When @use_cid_lock is 0, the cid allocation is lock-free. When contention is
* detected, it is set to 1 to ensure that all newly coming allocations are
* serialized by @cid_lock until the allocation which detected contention
* completes and sets @use_cid_lock back to 0. This guarantees forward progress
* of a cid allocation.
*/
int use_cid_lock;
/*
* mm_cid remote-clear implements a lock-free algorithm to clear per-mm/cpu cid
* concurrently with respect to the execution of the source runqueue context
* switch.
*
* There is one basic properties we want to guarantee here:
*
* (1) Remote-clear should _never_ mark a per-cpu cid UNSET when it is actively
* used by a task. That would lead to concurrent allocation of the cid and
* userspace corruption.
*
* Provide this guarantee by introducing a Dekker memory ordering to guarantee
* that a pair of loads observe at least one of a pair of stores, which can be
* shown as:
*
* X = Y = 0
*
* w[X]=1 w[Y]=1
* MB MB
* r[Y]=y r[X]=x
*
* Which guarantees that x==0 && y==0 is impossible. But rather than using
* values 0 and 1, this algorithm cares about specific state transitions of the
* runqueue current task (as updated by the scheduler context switch), and the
* per-mm/cpu cid value.
*
* Let's introduce task (Y) which has task->mm == mm and task (N) which has
* task->mm != mm for the rest of the discussion. There are two scheduler state
* transitions on context switch we care about:
*
* (TSA) Store to rq->curr with transition from (N) to (Y)
*
* (TSB) Store to rq->curr with transition from (Y) to (N)
*
* On the remote-clear side, there is one transition we care about:
*
* (TMA) cmpxchg to *pcpu_cid to set the LAZY flag
*
* There is also a transition to UNSET state which can be performed from all
* sides (scheduler, remote-clear). It is always performed with a cmpxchg which
* guarantees that only a single thread will succeed:
*
* (TMB) cmpxchg to *pcpu_cid to mark UNSET
*
* Just to be clear, what we do _not_ want to happen is a transition to UNSET
* when a thread is actively using the cid (property (1)).
*
* Let's looks at the relevant combinations of TSA/TSB, and TMA transitions.
*
* Scenario A) (TSA)+(TMA) (from next task perspective)
*
* CPU0 CPU1
*
* Context switch CS-1 Remote-clear
* - store to rq->curr: (N)->(Y) (TSA) - cmpxchg to *pcpu_id to LAZY (TMA)
* (implied barrier after cmpxchg)
* - switch_mm_cid()
* - memory barrier (see switch_mm_cid()
* comment explaining how this barrier
* is combined with other scheduler
* barriers)
* - mm_cid_get (next)
* - READ_ONCE(*pcpu_cid) - rcu_dereference(src_rq->curr)
*
* This Dekker ensures that either task (Y) is observed by the
* rcu_dereference() or the LAZY flag is observed by READ_ONCE(), or both are
* observed.
*
* If task (Y) store is observed by rcu_dereference(), it means that there is
* still an active task on the cpu. Remote-clear will therefore not transition
* to UNSET, which fulfills property (1).
*
* If task (Y) is not observed, but the lazy flag is observed by READ_ONCE(),
* it will move its state to UNSET, which clears the percpu cid perhaps
* uselessly (which is not an issue for correctness). Because task (Y) is not
* observed, CPU1 can move ahead to set the state to UNSET. Because moving
* state to UNSET is done with a cmpxchg expecting that the old state has the
* LAZY flag set, only one thread will successfully UNSET.
*
* If both states (LAZY flag and task (Y)) are observed, the thread on CPU0
* will observe the LAZY flag and transition to UNSET (perhaps uselessly), and
* CPU1 will observe task (Y) and do nothing more, which is fine.
*
* What we are effectively preventing with this Dekker is a scenario where
* neither LAZY flag nor store (Y) are observed, which would fail property (1)
* because this would UNSET a cid which is actively used.
*/
void sched_mm_cid_migrate_from(struct task_struct *t)
{
t->migrate_from_cpu = task_cpu(t);
}
static
int __sched_mm_cid_migrate_from_fetch_cid(struct rq *src_rq,
struct task_struct *t,
struct mm_cid *src_pcpu_cid)
{
struct mm_struct *mm = t->mm;
struct task_struct *src_task;
int src_cid, last_mm_cid;
if (!mm)
return -1;
last_mm_cid = t->last_mm_cid;
/*
* If the migrated task has no last cid, or if the current
* task on src rq uses the cid, it means the source cid does not need
* to be moved to the destination cpu.
*/
if (last_mm_cid == -1)
return -1;
src_cid = READ_ONCE(src_pcpu_cid->cid);
if (!mm_cid_is_valid(src_cid) || last_mm_cid != src_cid)
return -1;
/*
* If we observe an active task using the mm on this rq, it means we
* are not the last task to be migrated from this cpu for this mm, so
* there is no need to move src_cid to the destination cpu.
*/
guard(rcu)();
src_task = rcu_dereference(src_rq->curr);
if (READ_ONCE(src_task->mm_cid_active) && src_task->mm == mm) {
t->last_mm_cid = -1;
return -1;
}
return src_cid;
}
static
int __sched_mm_cid_migrate_from_try_steal_cid(struct rq *src_rq,
struct task_struct *t,
struct mm_cid *src_pcpu_cid,
int src_cid)
{
struct task_struct *src_task;
struct mm_struct *mm = t->mm;
int lazy_cid;
if (src_cid == -1)
return -1;
/*
* Attempt to clear the source cpu cid to move it to the destination
* cpu.
*/
lazy_cid = mm_cid_set_lazy_put(src_cid);
if (!try_cmpxchg(&src_pcpu_cid->cid, &src_cid, lazy_cid))
return -1;
/*
* The implicit barrier after cmpxchg per-mm/cpu cid before loading
* rq->curr->mm matches the scheduler barrier in context_switch()
* between store to rq->curr and load of prev and next task's
* per-mm/cpu cid.
*
* The implicit barrier after cmpxchg per-mm/cpu cid before loading
* rq->curr->mm_cid_active matches the barrier in
* sched_mm_cid_exit_signals(), sched_mm_cid_before_execve(), and
* sched_mm_cid_after_execve() between store to t->mm_cid_active and
* load of per-mm/cpu cid.
*/
/*
* If we observe an active task using the mm on this rq after setting
* the lazy-put flag, this task will be responsible for transitioning
* from lazy-put flag set to MM_CID_UNSET.
*/
scoped_guard (rcu) {
src_task = rcu_dereference(src_rq->curr);
if (READ_ONCE(src_task->mm_cid_active) && src_task->mm == mm) {
/*
* We observed an active task for this mm, there is therefore
* no point in moving this cid to the destination cpu.
*/
t->last_mm_cid = -1;
return -1;
}
}
/*
* The src_cid is unused, so it can be unset.
*/
if (!try_cmpxchg(&src_pcpu_cid->cid, &lazy_cid, MM_CID_UNSET))
return -1;
return src_cid;
}
/*
* Migration to dst cpu. Called with dst_rq lock held.
* Interrupts are disabled, which keeps the window of cid ownership without the
* source rq lock held small.
*/
void sched_mm_cid_migrate_to(struct rq *dst_rq, struct task_struct *t)
{
struct mm_cid *src_pcpu_cid, *dst_pcpu_cid;
struct mm_struct *mm = t->mm;
int src_cid, dst_cid, src_cpu;
struct rq *src_rq;
lockdep_assert_rq_held(dst_rq);
if (!mm)
return;
src_cpu = t->migrate_from_cpu;
if (src_cpu == -1) {
t->last_mm_cid = -1;
return;
}
/*
* Move the src cid if the dst cid is unset. This keeps id
* allocation closest to 0 in cases where few threads migrate around
* many CPUs.
*
* If destination cid is already set, we may have to just clear
* the src cid to ensure compactness in frequent migrations
* scenarios.
*
* It is not useful to clear the src cid when the number of threads is
* greater or equal to the number of allowed CPUs, because user-space
* can expect that the number of allowed cids can reach the number of
* allowed CPUs.
*/
dst_pcpu_cid = per_cpu_ptr(mm->pcpu_cid, cpu_of(dst_rq));
dst_cid = READ_ONCE(dst_pcpu_cid->cid);
if (!mm_cid_is_unset(dst_cid) &&
atomic_read(&mm->mm_users) >= t->nr_cpus_allowed)
return;
src_pcpu_cid = per_cpu_ptr(mm->pcpu_cid, src_cpu);
src_rq = cpu_rq(src_cpu);
src_cid = __sched_mm_cid_migrate_from_fetch_cid(src_rq, t, src_pcpu_cid);
if (src_cid == -1)
return;
src_cid = __sched_mm_cid_migrate_from_try_steal_cid(src_rq, t, src_pcpu_cid,
src_cid);
if (src_cid == -1)
return;
if (!mm_cid_is_unset(dst_cid)) {
__mm_cid_put(mm, src_cid);
return;
}
/* Move src_cid to dst cpu. */
mm_cid_snapshot_time(dst_rq, mm);
WRITE_ONCE(dst_pcpu_cid->cid, src_cid);
}
static void sched_mm_cid_remote_clear(struct mm_struct *mm, struct mm_cid *pcpu_cid,
int cpu)
{
struct rq *rq = cpu_rq(cpu);
struct task_struct *t;
int cid, lazy_cid;
cid = READ_ONCE(pcpu_cid->cid);
if (!mm_cid_is_valid(cid))
return;
/*
* Clear the cpu cid if it is set to keep cid allocation compact. If
* there happens to be other tasks left on the source cpu using this
* mm, the next task using this mm will reallocate its cid on context
* switch.
*/
lazy_cid = mm_cid_set_lazy_put(cid);
if (!try_cmpxchg(&pcpu_cid->cid, &cid, lazy_cid))
return;
/*
* The implicit barrier after cmpxchg per-mm/cpu cid before loading
* rq->curr->mm matches the scheduler barrier in context_switch()
* between store to rq->curr and load of prev and next task's
* per-mm/cpu cid.
*
* The implicit barrier after cmpxchg per-mm/cpu cid before loading
* rq->curr->mm_cid_active matches the barrier in
* sched_mm_cid_exit_signals(), sched_mm_cid_before_execve(), and
* sched_mm_cid_after_execve() between store to t->mm_cid_active and
* load of per-mm/cpu cid.
*/
/*
* If we observe an active task using the mm on this rq after setting
* the lazy-put flag, that task will be responsible for transitioning
* from lazy-put flag set to MM_CID_UNSET.
*/
scoped_guard (rcu) {
t = rcu_dereference(rq->curr);
if (READ_ONCE(t->mm_cid_active) && t->mm == mm)
return;
}
/*
* The cid is unused, so it can be unset.
* Disable interrupts to keep the window of cid ownership without rq
* lock small.
*/
scoped_guard (irqsave) {
if (try_cmpxchg(&pcpu_cid->cid, &lazy_cid, MM_CID_UNSET))
__mm_cid_put(mm, cid);
}
}
static void sched_mm_cid_remote_clear_old(struct mm_struct *mm, int cpu)
{
struct rq *rq = cpu_rq(cpu);
struct mm_cid *pcpu_cid;
struct task_struct *curr;
u64 rq_clock;
/*
* rq->clock load is racy on 32-bit but one spurious clear once in a
* while is irrelevant.
*/
rq_clock = READ_ONCE(rq->clock);
pcpu_cid = per_cpu_ptr(mm->pcpu_cid, cpu);
/*
* In order to take care of infrequently scheduled tasks, bump the time
* snapshot associated with this cid if an active task using the mm is
* observed on this rq.
*/
scoped_guard (rcu) {
curr = rcu_dereference(rq->curr);
if (READ_ONCE(curr->mm_cid_active) && curr->mm == mm) {
WRITE_ONCE(pcpu_cid->time, rq_clock);
return;
}
}
if (rq_clock < pcpu_cid->time + SCHED_MM_CID_PERIOD_NS)
return;
sched_mm_cid_remote_clear(mm, pcpu_cid, cpu);
}
static void sched_mm_cid_remote_clear_weight(struct mm_struct *mm, int cpu,
int weight)
{
struct mm_cid *pcpu_cid;
int cid;
pcpu_cid = per_cpu_ptr(mm->pcpu_cid, cpu);
cid = READ_ONCE(pcpu_cid->cid);
if (!mm_cid_is_valid(cid) || cid < weight)
return;
sched_mm_cid_remote_clear(mm, pcpu_cid, cpu);
}
static void task_mm_cid_work(struct callback_head *work)
{
unsigned long now = jiffies, old_scan, next_scan;
struct task_struct *t = current;
struct cpumask *cidmask;
struct mm_struct *mm;
int weight, cpu;
SCHED_WARN_ON(t != container_of(work, struct task_struct, cid_work));
work->next = work; /* Prevent double-add */
if (t->flags & PF_EXITING)
return;
mm = t->mm;
if (!mm)
return;
old_scan = READ_ONCE(mm->mm_cid_next_scan);
next_scan = now + msecs_to_jiffies(MM_CID_SCAN_DELAY);
if (!old_scan) {
unsigned long res;
res = cmpxchg(&mm->mm_cid_next_scan, old_scan, next_scan);
if (res != old_scan)
old_scan = res;
else
old_scan = next_scan;
}
if (time_before(now, old_scan))
return;
if (!try_cmpxchg(&mm->mm_cid_next_scan, &old_scan, next_scan))
return;
cidmask = mm_cidmask(mm);
/* Clear cids that were not recently used. */
for_each_possible_cpu(cpu)
sched_mm_cid_remote_clear_old(mm, cpu);
weight = cpumask_weight(cidmask);
/*
* Clear cids that are greater or equal to the cidmask weight to
* recompact it.
*/
for_each_possible_cpu(cpu)
sched_mm_cid_remote_clear_weight(mm, cpu, weight);
}
void init_sched_mm_cid(struct task_struct *t)
{
struct mm_struct *mm = t->mm;
int mm_users = 0;
if (mm) {
mm_users = atomic_read(&mm->mm_users);
if (mm_users == 1)
mm->mm_cid_next_scan = jiffies + msecs_to_jiffies(MM_CID_SCAN_DELAY);
}
t->cid_work.next = &t->cid_work; /* Protect against double add */
init_task_work(&t->cid_work, task_mm_cid_work);
}
void task_tick_mm_cid(struct rq *rq, struct task_struct *curr)
{
struct callback_head *work = &curr->cid_work;
unsigned long now = jiffies;
if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) ||
work->next != work)
return;
if (time_before(now, READ_ONCE(curr->mm->mm_cid_next_scan)))
return;
task_work_add(curr, work, TWA_RESUME);
}
void sched_mm_cid_exit_signals(struct task_struct *t)
{
struct mm_struct *mm = t->mm;
struct rq *rq;
if (!mm)
return;
preempt_disable();
rq = this_rq();
guard(rq_lock_irqsave)(rq);
preempt_enable_no_resched(); /* holding spinlock */
WRITE_ONCE(t->mm_cid_active, 0);
/*
* Store t->mm_cid_active before loading per-mm/cpu cid.
* Matches barrier in sched_mm_cid_remote_clear_old().
*/
smp_mb();
mm_cid_put(mm);
t->last_mm_cid = t->mm_cid = -1;
}
void sched_mm_cid_before_execve(struct task_struct *t)
{
struct mm_struct *mm = t->mm;
struct rq *rq;
if (!mm)
return;
preempt_disable();
rq = this_rq();
guard(rq_lock_irqsave)(rq);
preempt_enable_no_resched(); /* holding spinlock */
WRITE_ONCE(t->mm_cid_active, 0);
/*
* Store t->mm_cid_active before loading per-mm/cpu cid.
* Matches barrier in sched_mm_cid_remote_clear_old().
*/
smp_mb();
mm_cid_put(mm);
t->last_mm_cid = t->mm_cid = -1;
}
void sched_mm_cid_after_execve(struct task_struct *t)
{
struct mm_struct *mm = t->mm;
struct rq *rq;
if (!mm)
return;
preempt_disable();
rq = this_rq();
scoped_guard (rq_lock_irqsave, rq) {
preempt_enable_no_resched(); /* holding spinlock */
WRITE_ONCE(t->mm_cid_active, 1);
/*
* Store t->mm_cid_active before loading per-mm/cpu cid.
* Matches barrier in sched_mm_cid_remote_clear_old().
*/
smp_mb();
t->last_mm_cid = t->mm_cid = mm_cid_get(rq, mm);
}
rseq_set_notify_resume(t);
}
void sched_mm_cid_fork(struct task_struct *t)
{
WARN_ON_ONCE(!t->mm || t->mm_cid != -1);
t->mm_cid_active = 1;
}
#endif
#ifdef CONFIG_SCHED_CLASS_EXT
void sched_deq_and_put_task(struct task_struct *p, int queue_flags,
struct sched_enq_and_set_ctx *ctx)
{
struct rq *rq = task_rq(p);
lockdep_assert_rq_held(rq);
*ctx = (struct sched_enq_and_set_ctx){
.p = p,
.queue_flags = queue_flags,
.queued = task_on_rq_queued(p),
.running = task_current(rq, p),
};
update_rq_clock(rq);
if (ctx->queued)
dequeue_task(rq, p, queue_flags | DEQUEUE_NOCLOCK);
if (ctx->running)
put_prev_task(rq, p);
}
void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx)
{
struct rq *rq = task_rq(ctx->p);
lockdep_assert_rq_held(rq);
if (ctx->queued)
enqueue_task(rq, ctx->p, ctx->queue_flags | ENQUEUE_NOCLOCK);
if (ctx->running)
set_next_task(rq, ctx->p);
}
#endif /* CONFIG_SCHED_CLASS_EXT */
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