// SPDX-License-Identifier: GPL-2.0-only
/*
* RT-Mutexes: simple blocking mutual exclusion locks with PI support
*
* started by Ingo Molnar and Thomas Gleixner.
*
* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <[email protected]>
* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <[email protected]>
* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
* Copyright (C) 2006 Esben Nielsen
* Adaptive Spinlocks:
* Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
* and Peter Morreale,
* Adaptive Spinlocks simplification:
* Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <[email protected]>
*
* See Documentation/locking/rt-mutex-design.rst for details.
*/
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/deadline.h>
#include <linux/sched/signal.h>
#include <linux/sched/rt.h>
#include <linux/sched/wake_q.h>
#include <linux/ww_mutex.h>
#include <trace/events/lock.h>
#include "rtmutex_common.h"
#ifndef WW_RT
# define build_ww_mutex() (false)
# define ww_container_of(rtm) NULL
static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
struct rt_mutex *lock,
struct ww_acquire_ctx *ww_ctx)
{
return 0;
}
static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
struct ww_acquire_ctx *ww_ctx)
{
}
static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
struct ww_acquire_ctx *ww_ctx)
{
}
static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct ww_acquire_ctx *ww_ctx)
{
return 0;
}
#else
# define build_ww_mutex() (true)
# define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
# include "ww_mutex.h"
#endif
/*
* lock->owner state tracking:
*
* lock->owner holds the task_struct pointer of the owner. Bit 0
* is used to keep track of the "lock has waiters" state.
*
* owner bit0
* NULL 0 lock is free (fast acquire possible)
* NULL 1 lock is free and has waiters and the top waiter
* is going to take the lock*
* taskpointer 0 lock is held (fast release possible)
* taskpointer 1 lock is held and has waiters**
*
* The fast atomic compare exchange based acquire and release is only
* possible when bit 0 of lock->owner is 0.
*
* (*) It also can be a transitional state when grabbing the lock
* with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
* we need to set the bit0 before looking at the lock, and the owner may be
* NULL in this small time, hence this can be a transitional state.
*
* (**) There is a small time when bit 0 is set but there are no
* waiters. This can happen when grabbing the lock in the slow path.
* To prevent a cmpxchg of the owner releasing the lock, we need to
* set this bit before looking at the lock.
*/
static __always_inline struct task_struct *
rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
{
unsigned long val = (unsigned long)owner;
if (rt_mutex_has_waiters(lock))
val |= RT_MUTEX_HAS_WAITERS;
return (struct task_struct *)val;
}
static __always_inline void
rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
{
/*
* lock->wait_lock is held but explicit acquire semantics are needed
* for a new lock owner so WRITE_ONCE is insufficient.
*/
xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
}
static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
{
/* lock->wait_lock is held so the unlock provides release semantics. */
WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
}
static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
{
lock->owner = (struct task_struct *)
((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
}
static __always_inline void
fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
{
unsigned long owner, *p = (unsigned long *) &lock->owner;
if (rt_mutex_has_waiters(lock))
return;
/*
* The rbtree has no waiters enqueued, now make sure that the
* lock->owner still has the waiters bit set, otherwise the
* following can happen:
*
* CPU 0 CPU 1 CPU2
* l->owner=T1
* rt_mutex_lock(l)
* lock(l->lock)
* l->owner = T1 | HAS_WAITERS;
* enqueue(T2)
* boost()
* unlock(l->lock)
* block()
*
* rt_mutex_lock(l)
* lock(l->lock)
* l->owner = T1 | HAS_WAITERS;
* enqueue(T3)
* boost()
* unlock(l->lock)
* block()
* signal(->T2) signal(->T3)
* lock(l->lock)
* dequeue(T2)
* deboost()
* unlock(l->lock)
* lock(l->lock)
* dequeue(T3)
* ==> wait list is empty
* deboost()
* unlock(l->lock)
* lock(l->lock)
* fixup_rt_mutex_waiters()
* if (wait_list_empty(l) {
* l->owner = owner
* owner = l->owner & ~HAS_WAITERS;
* ==> l->owner = T1
* }
* lock(l->lock)
* rt_mutex_unlock(l) fixup_rt_mutex_waiters()
* if (wait_list_empty(l) {
* owner = l->owner & ~HAS_WAITERS;
* cmpxchg(l->owner, T1, NULL)
* ===> Success (l->owner = NULL)
*
* l->owner = owner
* ==> l->owner = T1
* }
*
* With the check for the waiter bit in place T3 on CPU2 will not
* overwrite. All tasks fiddling with the waiters bit are
* serialized by l->lock, so nothing else can modify the waiters
* bit. If the bit is set then nothing can change l->owner either
* so the simple RMW is safe. The cmpxchg() will simply fail if it
* happens in the middle of the RMW because the waiters bit is
* still set.
*/
owner = READ_ONCE(*p);
if (owner & RT_MUTEX_HAS_WAITERS) {
/*
* See rt_mutex_set_owner() and rt_mutex_clear_owner() on
* why xchg_acquire() is used for updating owner for
* locking and WRITE_ONCE() for unlocking.
*
* WRITE_ONCE() would work for the acquire case too, but
* in case that the lock acquisition failed it might
* force other lockers into the slow path unnecessarily.
*/
if (acquire_lock)
xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
else
WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
}
}
/*
* We can speed up the acquire/release, if there's no debugging state to be
* set up.
*/
#ifndef CONFIG_DEBUG_RT_MUTEXES
static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
struct task_struct *old,
struct task_struct *new)
{
return try_cmpxchg_acquire(&lock->owner, &old, new);
}
static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
{
return rt_mutex_cmpxchg_acquire(lock, NULL, current);
}
static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
struct task_struct *old,
struct task_struct *new)
{
return try_cmpxchg_release(&lock->owner, &old, new);
}
/*
* Callers must hold the ->wait_lock -- which is the whole purpose as we force
* all future threads that attempt to [Rmw] the lock to the slowpath. As such
* relaxed semantics suffice.
*/
static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
{
unsigned long *p = (unsigned long *) &lock->owner;
unsigned long owner, new;
owner = READ_ONCE(*p);
do {
new = owner | RT_MUTEX_HAS_WAITERS;
} while (!try_cmpxchg_relaxed(p, &owner, new));
/*
* The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
* operations in the event of contention. Ensure the successful
* cmpxchg is visible.
*/
smp_mb__after_atomic();
}
/*
* Safe fastpath aware unlock:
* 1) Clear the waiters bit
* 2) Drop lock->wait_lock
* 3) Try to unlock the lock with cmpxchg
*/
static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
unsigned long flags)
__releases(lock->wait_lock)
{
struct task_struct *owner = rt_mutex_owner(lock);
clear_rt_mutex_waiters(lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
/*
* If a new waiter comes in between the unlock and the cmpxchg
* we have two situations:
*
* unlock(wait_lock);
* lock(wait_lock);
* cmpxchg(p, owner, 0) == owner
* mark_rt_mutex_waiters(lock);
* acquire(lock);
* or:
*
* unlock(wait_lock);
* lock(wait_lock);
* mark_rt_mutex_waiters(lock);
*
* cmpxchg(p, owner, 0) != owner
* enqueue_waiter();
* unlock(wait_lock);
* lock(wait_lock);
* wake waiter();
* unlock(wait_lock);
* lock(wait_lock);
* acquire(lock);
*/
return rt_mutex_cmpxchg_release(lock, owner, NULL);
}
#else
static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
struct task_struct *old,
struct task_struct *new)
{
return false;
}
static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock);
static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
{
/*
* With debug enabled rt_mutex_cmpxchg trylock() will always fail.
*
* Avoid unconditionally taking the slow path by using
* rt_mutex_slow_trylock() which is covered by the debug code and can
* acquire a non-contended rtmutex.
*/
return rt_mutex_slowtrylock(lock);
}
static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
struct task_struct *old,
struct task_struct *new)
{
return false;
}
static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
{
lock->owner = (struct task_struct *)
((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
}
/*
* Simple slow path only version: lock->owner is protected by lock->wait_lock.
*/
static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
unsigned long flags)
__releases(lock->wait_lock)
{
lock->owner = NULL;
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
return true;
}
#endif
static __always_inline int __waiter_prio(struct task_struct *task)
{
int prio = task->prio;
if (!rt_or_dl_prio(prio))
return DEFAULT_PRIO;
return prio;
}
/*
* Update the waiter->tree copy of the sort keys.
*/
static __always_inline void
waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
{
lockdep_assert_held(&waiter->lock->wait_lock);
lockdep_assert(RB_EMPTY_NODE(&waiter->tree.entry));
waiter->tree.prio = __waiter_prio(task);
waiter->tree.deadline = task->dl.deadline;
}
/*
* Update the waiter->pi_tree copy of the sort keys (from the tree copy).
*/
static __always_inline void
waiter_clone_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
{
lockdep_assert_held(&waiter->lock->wait_lock);
lockdep_assert_held(&task->pi_lock);
lockdep_assert(RB_EMPTY_NODE(&waiter->pi_tree.entry));
waiter->pi_tree.prio = waiter->tree.prio;
waiter->pi_tree.deadline = waiter->tree.deadline;
}
/*
* Only use with rt_waiter_node_{less,equal}()
*/
#define task_to_waiter_node(p) \
&(struct rt_waiter_node){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
#define task_to_waiter(p) \
&(struct rt_mutex_waiter){ .tree = *task_to_waiter_node(p) }
static __always_inline int rt_waiter_node_less(struct rt_waiter_node *left,
struct rt_waiter_node *right)
{
if (left->prio < right->prio)
return 1;
/*
* If both waiters have dl_prio(), we check the deadlines of the
* associated tasks.
* If left waiter has a dl_prio(), and we didn't return 1 above,
* then right waiter has a dl_prio() too.
*/
if (dl_prio(left->prio))
return dl_time_before(left->deadline, right->deadline);
return 0;
}
static __always_inline int rt_waiter_node_equal(struct rt_waiter_node *left,
struct rt_waiter_node *right)
{
if (left->prio != right->prio)
return 0;
/*
* If both waiters have dl_prio(), we check the deadlines of the
* associated tasks.
* If left waiter has a dl_prio(), and we didn't return 0 above,
* then right waiter has a dl_prio() too.
*/
if (dl_prio(left->prio))
return left->deadline == right->deadline;
return 1;
}
static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
struct rt_mutex_waiter *top_waiter)
{
if (rt_waiter_node_less(&waiter->tree, &top_waiter->tree))
return true;
#ifdef RT_MUTEX_BUILD_SPINLOCKS
/*
* Note that RT tasks are excluded from same priority (lateral)
* steals to prevent the introduction of an unbounded latency.
*/
if (rt_or_dl_prio(waiter->tree.prio))
return false;
return rt_waiter_node_equal(&waiter->tree, &top_waiter->tree);
#else
return false;
#endif
}
#define __node_2_waiter(node) \
rb_entry((node), struct rt_mutex_waiter, tree.entry)
static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
{
struct rt_mutex_waiter *aw = __node_2_waiter(a);
struct rt_mutex_waiter *bw = __node_2_waiter(b);
if (rt_waiter_node_less(&aw->tree, &bw->tree))
return 1;
if (!build_ww_mutex())
return 0;
if (rt_waiter_node_less(&bw->tree, &aw->tree))
return 0;
/* NOTE: relies on waiter->ww_ctx being set before insertion */
if (aw->ww_ctx) {
if (!bw->ww_ctx)
return 1;
return (signed long)(aw->ww_ctx->stamp -
bw->ww_ctx->stamp) < 0;
}
return 0;
}
static __always_inline void
rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
{
lockdep_assert_held(&lock->wait_lock);
rb_add_cached(&waiter->tree.entry, &lock->waiters, __waiter_less);
}
static __always_inline void
rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
{
lockdep_assert_held(&lock->wait_lock);
if (RB_EMPTY_NODE(&waiter->tree.entry))
return;
rb_erase_cached(&waiter->tree.entry, &lock->waiters);
RB_CLEAR_NODE(&waiter->tree.entry);
}
#define __node_2_rt_node(node) \
rb_entry((node), struct rt_waiter_node, entry)
static __always_inline bool __pi_waiter_less(struct rb_node *a, const struct rb_node *b)
{
return rt_waiter_node_less(__node_2_rt_node(a), __node_2_rt_node(b));
}
static __always_inline void
rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
{
lockdep_assert_held(&task->pi_lock);
rb_add_cached(&waiter->pi_tree.entry, &task->pi_waiters, __pi_waiter_less);
}
static __always_inline void
rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
{
lockdep_assert_held(&task->pi_lock);
if (RB_EMPTY_NODE(&waiter->pi_tree.entry))
return;
rb_erase_cached(&waiter->pi_tree.entry, &task->pi_waiters);
RB_CLEAR_NODE(&waiter->pi_tree.entry);
}
static __always_inline void rt_mutex_adjust_prio(struct rt_mutex_base *lock,
struct task_struct *p)
{
struct task_struct *pi_task = NULL;
lockdep_assert_held(&lock->wait_lock);
lockdep_assert(rt_mutex_owner(lock) == p);
lockdep_assert_held(&p->pi_lock);
if (task_has_pi_waiters(p))
pi_task = task_top_pi_waiter(p)->task;
rt_mutex_setprio(p, pi_task);
}
/* RT mutex specific wake_q wrappers */
static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
struct task_struct *task,
unsigned int wake_state)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
WARN_ON_ONCE(wqh->rtlock_task);
get_task_struct(task);
wqh->rtlock_task = task;
} else {
wake_q_add(&wqh->head, task);
}
}
static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
struct rt_mutex_waiter *w)
{
rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
}
static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
put_task_struct(wqh->rtlock_task);
wqh->rtlock_task = NULL;
}
if (!wake_q_empty(&wqh->head))
wake_up_q(&wqh->head);
/* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
preempt_enable();
}
/*
* Deadlock detection is conditional:
*
* If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
* if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
*
* If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
* conducted independent of the detect argument.
*
* If the waiter argument is NULL this indicates the deboost path and
* deadlock detection is disabled independent of the detect argument
* and the config settings.
*/
static __always_inline bool
rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
enum rtmutex_chainwalk chwalk)
{
if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
return waiter != NULL;
return chwalk == RT_MUTEX_FULL_CHAINWALK;
}
static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
{
return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
}
/*
* Adjust the priority chain. Also used for deadlock detection.
* Decreases task's usage by one - may thus free the task.
*
* @task: the task owning the mutex (owner) for which a chain walk is
* probably needed
* @chwalk: do we have to carry out deadlock detection?
* @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
* things for a task that has just got its priority adjusted, and
* is waiting on a mutex)
* @next_lock: the mutex on which the owner of @orig_lock was blocked before
* we dropped its pi_lock. Is never dereferenced, only used for
* comparison to detect lock chain changes.
* @orig_waiter: rt_mutex_waiter struct for the task that has just donated
* its priority to the mutex owner (can be NULL in the case
* depicted above or if the top waiter is gone away and we are
* actually deboosting the owner)
* @top_task: the current top waiter
*
* Returns 0 or -EDEADLK.
*
* Chain walk basics and protection scope
*
* [R] refcount on task
* [Pn] task->pi_lock held
* [L] rtmutex->wait_lock held
*
* Normal locking order:
*
* rtmutex->wait_lock
* task->pi_lock
*
* Step Description Protected by
* function arguments:
* @task [R]
* @orig_lock if != NULL @top_task is blocked on it
* @next_lock Unprotected. Cannot be
* dereferenced. Only used for
* comparison.
* @orig_waiter if != NULL @top_task is blocked on it
* @top_task current, or in case of proxy
* locking protected by calling
* code
* again:
* loop_sanity_check();
* retry:
* [1] lock(task->pi_lock); [R] acquire [P1]
* [2] waiter = task->pi_blocked_on; [P1]
* [3] check_exit_conditions_1(); [P1]
* [4] lock = waiter->lock; [P1]
* [5] if (!try_lock(lock->wait_lock)) { [P1] try to acquire [L]
* unlock(task->pi_lock); release [P1]
* goto retry;
* }
* [6] check_exit_conditions_2(); [P1] + [L]
* [7] requeue_lock_waiter(lock, waiter); [P1] + [L]
* [8] unlock(task->pi_lock); release [P1]
* put_task_struct(task); release [R]
* [9] check_exit_conditions_3(); [L]
* [10] task = owner(lock); [L]
* get_task_struct(task); [L] acquire [R]
* lock(task->pi_lock); [L] acquire [P2]
* [11] requeue_pi_waiter(tsk, waiters(lock));[P2] + [L]
* [12] check_exit_conditions_4(); [P2] + [L]
* [13] unlock(task->pi_lock); release [P2]
* unlock(lock->wait_lock); release [L]
* goto again;
*
* Where P1 is the blocking task and P2 is the lock owner; going up one step
* the owner becomes the next blocked task etc..
*
*
*/
static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
enum rtmutex_chainwalk chwalk,
struct rt_mutex_base *orig_lock,
struct rt_mutex_base *next_lock,
struct rt_mutex_waiter *orig_waiter,
struct task_struct *top_task)
{
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
struct rt_mutex_waiter *prerequeue_top_waiter;
int ret = 0, depth = 0;
struct rt_mutex_base *lock;
bool detect_deadlock;
bool requeue = true;
detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
/*
* The (de)boosting is a step by step approach with a lot of
* pitfalls. We want this to be preemptible and we want hold a
* maximum of two locks per step. So we have to check
* carefully whether things change under us.
*/
again:
/*
* We limit the lock chain length for each invocation.
*/
if (++depth > max_lock_depth) {
static int prev_max;
/*
* Print this only once. If the admin changes the limit,
* print a new message when reaching the limit again.
*/
if (prev_max != max_lock_depth) {
prev_max = max_lock_depth;
printk(KERN_WARNING "Maximum lock depth %d reached "
"task: %s (%d)\n", max_lock_depth,
top_task->comm, task_pid_nr(top_task));
}
put_task_struct(task);
return -EDEADLK;
}
/*
* We are fully preemptible here and only hold the refcount on
* @task. So everything can have changed under us since the
* caller or our own code below (goto retry/again) dropped all
* locks.
*/
retry:
/*
* [1] Task cannot go away as we did a get_task() before !
*/
raw_spin_lock_irq(&task->pi_lock);
/*
* [2] Get the waiter on which @task is blocked on.
*/
waiter = task->pi_blocked_on;
/*
* [3] check_exit_conditions_1() protected by task->pi_lock.
*/
/*
* Check whether the end of the boosting chain has been
* reached or the state of the chain has changed while we
* dropped the locks.
*/
if (!waiter)
goto out_unlock_pi;
/*
* Check the orig_waiter state. After we dropped the locks,
* the previous owner of the lock might have released the lock.
*/
if (orig_waiter && !rt_mutex_owner(orig_lock))
goto out_unlock_pi;
/*
* We dropped all locks after taking a refcount on @task, so
* the task might have moved on in the lock chain or even left
* the chain completely and blocks now on an unrelated lock or
* on @orig_lock.
*
* We stored the lock on which @task was blocked in @next_lock,
* so we can detect the chain change.
*/
if (next_lock != waiter->lock)
goto out_unlock_pi;
/*
* There could be 'spurious' loops in the lock graph due to ww_mutex,
* consider:
*
* P1: A, ww_A, ww_B
* P2: ww_B, ww_A
* P3: A
*
* P3 should not return -EDEADLK because it gets trapped in the cycle
* created by P1 and P2 (which will resolve -- and runs into
* max_lock_depth above). Therefore disable detect_deadlock such that
* the below termination condition can trigger once all relevant tasks
* are boosted.
*
* Even when we start with ww_mutex we can disable deadlock detection,
* since we would supress a ww_mutex induced deadlock at [6] anyway.
* Supressing it here however is not sufficient since we might still
* hit [6] due to adjustment driven iteration.
*
* NOTE: if someone were to create a deadlock between 2 ww_classes we'd
* utterly fail to report it; lockdep should.
*/
if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
detect_deadlock = false;
/*
* Drop out, when the task has no waiters. Note,
* top_waiter can be NULL, when we are in the deboosting
* mode!
*/
if (top_waiter) {
if (!task_has_pi_waiters(task))
goto out_unlock_pi;
/*
* If deadlock detection is off, we stop here if we
* are not the top pi waiter of the task. If deadlock
* detection is enabled we continue, but stop the
* requeueing in the chain walk.
*/
if (top_waiter != task_top_pi_waiter(task)) {
if (!detect_deadlock)
goto out_unlock_pi;
else
requeue = false;
}
}
/*
* If the waiter priority is the same as the task priority
* then there is no further priority adjustment necessary. If
* deadlock detection is off, we stop the chain walk. If its
* enabled we continue, but stop the requeueing in the chain
* walk.
*/
if (rt_waiter_node_equal(&waiter->tree, task_to_waiter_node(task))) {
if (!detect_deadlock)
goto out_unlock_pi;
else
requeue = false;
}
/*
* [4] Get the next lock; per holding task->pi_lock we can't unblock
* and guarantee @lock's existence.
*/
lock = waiter->lock;
/*
* [5] We need to trylock here as we are holding task->pi_lock,
* which is the reverse lock order versus the other rtmutex
* operations.
*
* Per the above, holding task->pi_lock guarantees lock exists, so
* inverting this lock order is infeasible from a life-time
* perspective.
*/
if (!raw_spin_trylock(&lock->wait_lock)) {
raw_spin_unlock_irq(&task->pi_lock);
cpu_relax();
goto retry;
}
/*
* [6] check_exit_conditions_2() protected by task->pi_lock and
* lock->wait_lock.
*
* Deadlock detection. If the lock is the same as the original
* lock which caused us to walk the lock chain or if the
* current lock is owned by the task which initiated the chain
* walk, we detected a deadlock.
*/
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
ret = -EDEADLK;
/*
* When the deadlock is due to ww_mutex; also see above. Don't
* report the deadlock and instead let the ww_mutex wound/die
* logic pick which of the contending threads gets -EDEADLK.
*
* NOTE: assumes the cycle only contains a single ww_class; any
* other configuration and we fail to report; also, see
* lockdep.
*/
if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
ret = 0;
raw_spin_unlock(&lock->wait_lock);
goto out_unlock_pi;
}
/*
* If we just follow the lock chain for deadlock detection, no
* need to do all the requeue operations. To avoid a truckload
* of conditionals around the various places below, just do the
* minimum chain walk checks.
*/
if (!requeue) {
/*
* No requeue[7] here. Just release @task [8]
*/
raw_spin_unlock(&task->pi_lock);
put_task_struct(task);
/*
* [9] check_exit_conditions_3 protected by lock->wait_lock.
* If there is no owner of the lock, end of chain.
*/
if (!rt_mutex_owner(lock)) {
raw_spin_unlock_irq(&lock->wait_lock);
return 0;
}
/* [10] Grab the next task, i.e. owner of @lock */
task = get_task_struct(rt_mutex_owner(lock));
raw_spin_lock(&task->pi_lock);
/*
* No requeue [11] here. We just do deadlock detection.
*
* [12] Store whether owner is blocked
* itself. Decision is made after dropping the locks
*/
next_lock = task_blocked_on_lock(task);
/*
* Get the top waiter for the next iteration
*/
top_waiter = rt_mutex_top_waiter(lock);
/* [13] Drop locks */
raw_spin_unlock(&task->pi_lock);
raw_spin_unlock_irq(&lock->wait_lock);
/* If owner is not blocked, end of chain. */
if (!next_lock)
goto out_put_task;
goto again;
}
/*
* Store the current top waiter before doing the requeue
* operation on @lock. We need it for the boost/deboost
* decision below.
*/
prerequeue_top_waiter = rt_mutex_top_waiter(lock);
/* [7] Requeue the waiter in the lock waiter tree. */
rt_mutex_dequeue(lock, waiter);
/*
* Update the waiter prio fields now that we're dequeued.
*
* These values can have changed through either:
*
* sys_sched_set_scheduler() / sys_sched_setattr()
*
* or
*
* DL CBS enforcement advancing the effective deadline.
*/
waiter_update_prio(waiter, task);
rt_mutex_enqueue(lock, waiter);
/*
* [8] Release the (blocking) task in preparation for
* taking the owner task in [10].
*
* Since we hold lock->waiter_lock, task cannot unblock, even if we
* release task->pi_lock.
*/
raw_spin_unlock(&task->pi_lock);
put_task_struct(task);
/*
* [9] check_exit_conditions_3 protected by lock->wait_lock.
*
* We must abort the chain walk if there is no lock owner even
* in the dead lock detection case, as we have nothing to
* follow here. This is the end of the chain we are walking.
*/
if (!rt_mutex_owner(lock)) {
/*
* If the requeue [7] above changed the top waiter,
* then we need to wake the new top waiter up to try
* to get the lock.
*/
top_waiter = rt_mutex_top_waiter(lock);
if (prerequeue_top_waiter != top_waiter)
wake_up_state(top_waiter->task, top_waiter->wake_state);
raw_spin_unlock_irq(&lock->wait_lock);
return 0;
}
/*
* [10] Grab the next task, i.e. the owner of @lock
*
* Per holding lock->wait_lock and checking for !owner above, there
* must be an owner and it cannot go away.
*/
task = get_task_struct(rt_mutex_owner(lock));
raw_spin_lock(&task->pi_lock);
/* [11] requeue the pi waiters if necessary */
if (waiter == rt_mutex_top_waiter(lock)) {
/*
* The waiter became the new top (highest priority)
* waiter on the lock. Replace the previous top waiter
* in the owner tasks pi waiters tree with this waiter
* and adjust the priority of the owner.
*/
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
waiter_clone_prio(waiter, task);
rt_mutex_enqueue_pi(task, waiter);
rt_mutex_adjust_prio(lock, task);
} else if (prerequeue_top_waiter == waiter) {
/*
* The waiter was the top waiter on the lock, but is
* no longer the top priority waiter. Replace waiter in
* the owner tasks pi waiters tree with the new top
* (highest priority) waiter and adjust the priority
* of the owner.
* The new top waiter is stored in @waiter so that
* @waiter == @top_waiter evaluates to true below and
* we continue to deboost the rest of the chain.
*/
rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
waiter_clone_prio(waiter, task);
rt_mutex_enqueue_pi(task, waiter);
rt_mutex_adjust_prio(lock, task);
} else {
/*
* Nothing changed. No need to do any priority
* adjustment.
*/
}
/*
* [12] check_exit_conditions_4() protected by task->pi_lock
* and lock->wait_lock. The actual decisions are made after we
* dropped the locks.
*
* Check whether the task which owns the current lock is pi
* blocked itself. If yes we store a pointer to the lock for
* the lock chain change detection above. After we dropped
* task->pi_lock next_lock cannot be dereferenced anymore.
*/
next_lock = task_blocked_on_lock(task);
/*
* Store the top waiter of @lock for the end of chain walk
* decision below.
*/
top_waiter = rt_mutex_top_waiter(lock);
/* [13] Drop the locks */
raw_spin_unlock(&task->pi_lock);
raw_spin_unlock_irq(&lock->wait_lock);
/*
* Make the actual exit decisions [12], based on the stored
* values.
*
* We reached the end of the lock chain. Stop right here. No
* point to go back just to figure that out.
*/
if (!next_lock)
goto out_put_task;
/*
* If the current waiter is not the top waiter on the lock,
* then we can stop the chain walk here if we are not in full
* deadlock detection mode.
*/
if (!detect_deadlock && waiter != top_waiter)
goto out_put_task;
goto again;
out_unlock_pi:
raw_spin_unlock_irq(&task->pi_lock);
out_put_task:
put_task_struct(task);
return ret;
}
/*
* Try to take an rt-mutex
*
* Must be called with lock->wait_lock held and interrupts disabled
*
* @lock: The lock to be acquired.
* @task: The task which wants to acquire the lock
* @waiter: The waiter that is queued to the lock's wait tree if the
* callsite called task_blocked_on_lock(), otherwise NULL
*/
static int __sched
try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
struct rt_mutex_waiter *waiter)
{
lockdep_assert_held(&lock->wait_lock);
/*
* Before testing whether we can acquire @lock, we set the
* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
* other tasks which try to modify @lock into the slow path
* and they serialize on @lock->wait_lock.
*
* The RT_MUTEX_HAS_WAITERS bit can have a transitional state
* as explained at the top of this file if and only if:
*
* - There is a lock owner. The caller must fixup the
* transient state if it does a trylock or leaves the lock
* function due to a signal or timeout.
*
* - @task acquires the lock and there are no other
* waiters. This is undone in rt_mutex_set_owner(@task) at
* the end of this function.
*/
mark_rt_mutex_waiters(lock);
/*
* If @lock has an owner, give up.
*/
if (rt_mutex_owner(lock))
return 0;
/*
* If @waiter != NULL, @task has already enqueued the waiter
* into @lock waiter tree. If @waiter == NULL then this is a
* trylock attempt.
*/
if (waiter) {
struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
/*
* If waiter is the highest priority waiter of @lock,
* or allowed to steal it, take it over.
*/
if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
/*
* We can acquire the lock. Remove the waiter from the
* lock waiters tree.
*/
rt_mutex_dequeue(lock, waiter);
} else {
return 0;
}
} else {
/*
* If the lock has waiters already we check whether @task is
* eligible to take over the lock.
*
* If there are no other waiters, @task can acquire
* the lock. @task->pi_blocked_on is NULL, so it does
* not need to be dequeued.
*/
if (rt_mutex_has_waiters(lock)) {
/* Check whether the trylock can steal it. */
if (!rt_mutex_steal(task_to_waiter(task),
rt_mutex_top_waiter(lock)))
return 0;
/*
* The current top waiter stays enqueued. We
* don't have to change anything in the lock
* waiters order.
*/
} else {
/*
* No waiters. Take the lock without the
* pi_lock dance.@task->pi_blocked_on is NULL
* and we have no waiters to enqueue in @task
* pi waiters tree.
*/
goto takeit;
}
}
/*
* Clear @task->pi_blocked_on. Requires protection by
* @task->pi_lock. Redundant operation for the @waiter == NULL
* case, but conditionals are more expensive than a redundant
* store.
*/
raw_spin_lock(&task->pi_lock);
task->pi_blocked_on = NULL;
/*
* Finish the lock acquisition. @task is the new owner. If
* other waiters exist we have to insert the highest priority
* waiter into @task->pi_waiters tree.
*/
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
raw_spin_unlock(&task->pi_lock);
takeit:
/*
* This either preserves the RT_MUTEX_HAS_WAITERS bit if there
* are still waiters or clears it.
*/
rt_mutex_set_owner(lock, task);
return 1;
}
/*
* Task blocks on lock.
*
* Prepare waiter and propagate pi chain
*
* This must be called with lock->wait_lock held and interrupts disabled
*/
static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
struct ww_acquire_ctx *ww_ctx,
enum rtmutex_chainwalk chwalk)
{
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_waiter *top_waiter = waiter;
struct rt_mutex_base *next_lock;
int chain_walk = 0, res;
lockdep_assert_held(&lock->wait_lock);
/*
* Early deadlock detection. We really don't want the task to
* enqueue on itself just to untangle the mess later. It's not
* only an optimization. We drop the locks, so another waiter
* can come in before the chain walk detects the deadlock. So
* the other will detect the deadlock and return -EDEADLOCK,
* which is wrong, as the other waiter is not in a deadlock
* situation.
*
* Except for ww_mutex, in that case the chain walk must already deal
* with spurious cycles, see the comments at [3] and [6].
*/
if (owner == task && !(build_ww_mutex() && ww_ctx))
return -EDEADLK;
raw_spin_lock(&task->pi_lock);
waiter->task = task;
waiter->lock = lock;
waiter_update_prio(waiter, task);
waiter_clone_prio(waiter, task);
/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
top_waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue(lock, waiter);
task->pi_blocked_on = waiter;
raw_spin_unlock(&task->pi_lock);
if (build_ww_mutex() && ww_ctx) {
struct rt_mutex *rtm;
/* Check whether the waiter should back out immediately */
rtm = container_of(lock, struct rt_mutex, rtmutex);
res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
if (res) {
raw_spin_lock(&task->pi_lock);
rt_mutex_dequeue(lock, waiter);
task->pi_blocked_on = NULL;
raw_spin_unlock(&task->pi_lock);
return res;
}
}
if (!owner)
return 0;
raw_spin_lock(&owner->pi_lock);
if (waiter == rt_mutex_top_waiter(lock)) {
rt_mutex_dequeue_pi(owner, top_waiter);
rt_mutex_enqueue_pi(owner, waiter);
rt_mutex_adjust_prio(lock, owner);
if (owner->pi_blocked_on)
chain_walk = 1;
} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
chain_walk = 1;
}
/* Store the lock on which owner is blocked or NULL */
next_lock = task_blocked_on_lock(owner);
raw_spin_unlock(&owner->pi_lock);
/*
* Even if full deadlock detection is on, if the owner is not
* blocked itself, we can avoid finding this out in the chain
* walk.
*/
if (!chain_walk || !next_lock)
return 0;
/*
* The owner can't disappear while holding a lock,
* so the owner struct is protected by wait_lock.
* Gets dropped in rt_mutex_adjust_prio_chain()!
*/
get_task_struct(owner);
raw_spin_unlock_irq(&lock->wait_lock);
res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
next_lock, waiter, task);
raw_spin_lock_irq(&lock->wait_lock);
return res;
}
/*
* Remove the top waiter from the current tasks pi waiter tree and
* queue it up.
*
* Called with lock->wait_lock held and interrupts disabled.
*/
static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
struct rt_mutex_base *lock)
{
struct rt_mutex_waiter *waiter;
lockdep_assert_held(&lock->wait_lock);
raw_spin_lock(¤t->pi_lock);
waiter = rt_mutex_top_waiter(lock);
/*
* Remove it from current->pi_waiters and deboost.
*
* We must in fact deboost here in order to ensure we call
* rt_mutex_setprio() to update p->pi_top_task before the
* task unblocks.
*/
rt_mutex_dequeue_pi(current, waiter);
rt_mutex_adjust_prio(lock, current);
/*
* As we are waking up the top waiter, and the waiter stays
* queued on the lock until it gets the lock, this lock
* obviously has waiters. Just set the bit here and this has
* the added benefit of forcing all new tasks into the
* slow path making sure no task of lower priority than
* the top waiter can steal this lock.
*/
lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
/*
* We deboosted before waking the top waiter task such that we don't
* run two tasks with the 'same' priority (and ensure the
* p->pi_top_task pointer points to a blocked task). This however can
* lead to priority inversion if we would get preempted after the
* deboost but before waking our donor task, hence the preempt_disable()
* before unlock.
*
* Pairs with preempt_enable() in rt_mutex_wake_up_q();
*/
preempt_disable();
rt_mutex_wake_q_add(wqh, waiter);
raw_spin_unlock(¤t->pi_lock);
}
static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
{
int ret = try_to_take_rt_mutex(lock, current, NULL);
/*
* try_to_take_rt_mutex() sets the lock waiters bit
* unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock, true);
return ret;
}
/*
* Slow path try-lock function:
*/
static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
{
unsigned long flags;
int ret;
/*
* If the lock already has an owner we fail to get the lock.
* This can be done without taking the @lock->wait_lock as
* it is only being read, and this is a trylock anyway.
*/
if (rt_mutex_owner(lock))
return 0;
/*
* The mutex has currently no owner. Lock the wait lock and try to
* acquire the lock. We use irqsave here to support early boot calls.
*/
raw_spin_lock_irqsave(&lock->wait_lock, flags);
ret = __rt_mutex_slowtrylock(lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
return ret;
}
static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
{
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
return 1;
return rt_mutex_slowtrylock(lock);
}
/*
* Slow path to release a rt-mutex.
*/
static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
{
DEFINE_RT_WAKE_Q(wqh);
unsigned long flags;
/* irqsave required to support early boot calls */
raw_spin_lock_irqsave(&lock->wait_lock, flags);
debug_rt_mutex_unlock(lock);
/*
* We must be careful here if the fast path is enabled. If we
* have no waiters queued we cannot set owner to NULL here
* because of:
*
* foo->lock->owner = NULL;
* rtmutex_lock(foo->lock); <- fast path
* free = atomic_dec_and_test(foo->refcnt);
* rtmutex_unlock(foo->lock); <- fast path
* if (free)
* kfree(foo);
* raw_spin_unlock(foo->lock->wait_lock);
*
* So for the fastpath enabled kernel:
*
* Nothing can set the waiters bit as long as we hold
* lock->wait_lock. So we do the following sequence:
*
* owner = rt_mutex_owner(lock);
* clear_rt_mutex_waiters(lock);
* raw_spin_unlock(&lock->wait_lock);
* if (cmpxchg(&lock->owner, owner, 0) == owner)
* return;
* goto retry;
*
* The fastpath disabled variant is simple as all access to
* lock->owner is serialized by lock->wait_lock:
*
* lock->owner = NULL;
* raw_spin_unlock(&lock->wait_lock);
*/
while (!rt_mutex_has_waiters(lock)) {
/* Drops lock->wait_lock ! */
if (unlock_rt_mutex_safe(lock, flags) == true)
return;
/* Relock the rtmutex and try again */
raw_spin_lock_irqsave(&lock->wait_lock, flags);
}
/*
* The wakeup next waiter path does not suffer from the above
* race. See the comments there.
*
* Queue the next waiter for wakeup once we release the wait_lock.
*/
mark_wakeup_next_waiter(&wqh, lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
rt_mutex_wake_up_q(&wqh);
}
static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
{
if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
return;
rt_mutex_slowunlock(lock);
}
#ifdef CONFIG_SMP
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *owner)
{
bool res = true;
rcu_read_lock();
for (;;) {
/* If owner changed, trylock again. */
if (owner != rt_mutex_owner(lock))
break;
/*
* Ensure that @owner is dereferenced after checking that
* the lock owner still matches @owner. If that fails,
* @owner might point to freed memory. If it still matches,
* the rcu_read_lock() ensures the memory stays valid.
*/
barrier();
/*
* Stop spinning when:
* - the lock owner has been scheduled out
* - current is not longer the top waiter
* - current is requested to reschedule (redundant
* for CONFIG_PREEMPT_RCU=y)
* - the VCPU on which owner runs is preempted
*/
if (!owner_on_cpu(owner) || need_resched() ||
!rt_mutex_waiter_is_top_waiter(lock, waiter)) {
res = false;
break;
}
cpu_relax();
}
rcu_read_unlock();
return res;
}
#else
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *owner)
{
return false;
}
#endif
#ifdef RT_MUTEX_BUILD_MUTEX
/*
* Functions required for:
* - rtmutex, futex on all kernels
* - mutex and rwsem substitutions on RT kernels
*/
/*
* Remove a waiter from a lock and give up
*
* Must be called with lock->wait_lock held and interrupts disabled. It must
* have just failed to try_to_take_rt_mutex().
*/
static void __sched remove_waiter(struct rt_mutex_base *lock,
struct rt_mutex_waiter *waiter)
{
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_base *next_lock;
lockdep_assert_held(&lock->wait_lock);
raw_spin_lock(¤t->pi_lock);
rt_mutex_dequeue(lock, waiter);
current->pi_blocked_on = NULL;
raw_spin_unlock(¤t->pi_lock);
/*
* Only update priority if the waiter was the highest priority
* waiter of the lock and there is an owner to update.
*/
if (!owner || !is_top_waiter)
return;
raw_spin_lock(&owner->pi_lock);
rt_mutex_dequeue_pi(owner, waiter);
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
rt_mutex_adjust_prio(lock, owner);
/* Store the lock on which owner is blocked or NULL */
next_lock = task_blocked_on_lock(owner);
raw_spin_unlock(&owner->pi_lock);
/*
* Don't walk the chain, if the owner task is not blocked
* itself.
*/
if (!next_lock)
return;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
raw_spin_unlock_irq(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
next_lock, NULL, current);
raw_spin_lock_irq(&lock->wait_lock);
}
/**
* rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
* @lock: the rt_mutex to take
* @ww_ctx: WW mutex context pointer
* @state: the state the task should block in (TASK_INTERRUPTIBLE
* or TASK_UNINTERRUPTIBLE)
* @timeout: the pre-initialized and started timer, or NULL for none
* @waiter: the pre-initialized rt_mutex_waiter
*
* Must be called with lock->wait_lock held and interrupts disabled
*/
static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state,
struct hrtimer_sleeper *timeout,
struct rt_mutex_waiter *waiter)
{
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
struct task_struct *owner;
int ret = 0;
for (;;) {
/* Try to acquire the lock: */
if (try_to_take_rt_mutex(lock, current, waiter))
break;
if (timeout && !timeout->task) {
ret = -ETIMEDOUT;
break;
}
if (signal_pending_state(state, current)) {
ret = -EINTR;
break;
}
if (build_ww_mutex() && ww_ctx) {
ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
if (ret)
break;
}
if (waiter == rt_mutex_top_waiter(lock))
owner = rt_mutex_owner(lock);
else
owner = NULL;
raw_spin_unlock_irq(&lock->wait_lock);
if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
rt_mutex_schedule();
raw_spin_lock_irq(&lock->wait_lock);
set_current_state(state);
}
__set_current_state(TASK_RUNNING);
return ret;
}
static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
struct rt_mutex_base *lock,
struct rt_mutex_waiter *w)
{
/*
* If the result is not -EDEADLOCK or the caller requested
* deadlock detection, nothing to do here.
*/
if (res != -EDEADLOCK || detect_deadlock)
return;
if (build_ww_mutex() && w->ww_ctx)
return;
raw_spin_unlock_irq(&lock->wait_lock);
WARN(1, "rtmutex deadlock detected\n");
while (1) {
set_current_state(TASK_INTERRUPTIBLE);
rt_mutex_schedule();
}
}
/**
* __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
* @lock: The rtmutex to block lock
* @ww_ctx: WW mutex context pointer
* @state: The task state for sleeping
* @chwalk: Indicator whether full or partial chainwalk is requested
* @waiter: Initializer waiter for blocking
*/
static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state,
enum rtmutex_chainwalk chwalk,
struct rt_mutex_waiter *waiter)
{
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
struct ww_mutex *ww = ww_container_of(rtm);
int ret;
lockdep_assert_held(&lock->wait_lock);
/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock, current, NULL)) {
if (build_ww_mutex() && ww_ctx) {
__ww_mutex_check_waiters(rtm, ww_ctx);
ww_mutex_lock_acquired(ww, ww_ctx);
}
return 0;
}
set_current_state(state);
trace_contention_begin(lock, LCB_F_RT);
ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
if (likely(!ret))
ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
if (likely(!ret)) {
/* acquired the lock */
if (build_ww_mutex() && ww_ctx) {
if (!ww_ctx->is_wait_die)
__ww_mutex_check_waiters(rtm, ww_ctx);
ww_mutex_lock_acquired(ww, ww_ctx);
}
} else {
__set_current_state(TASK_RUNNING);
remove_waiter(lock, waiter);
rt_mutex_handle_deadlock(ret, chwalk, lock, waiter);
}
/*
* try_to_take_rt_mutex() sets the waiter bit
* unconditionally. We might have to fix that up.
*/
fixup_rt_mutex_waiters(lock, true);
trace_contention_end(lock, ret);
return ret;
}
static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state)
{
struct rt_mutex_waiter waiter;
int ret;
rt_mutex_init_waiter(&waiter);
waiter.ww_ctx = ww_ctx;
ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
&waiter);
debug_rt_mutex_free_waiter(&waiter);
return ret;
}
/*
* rt_mutex_slowlock - Locking slowpath invoked when fast path fails
* @lock: The rtmutex to block lock
* @ww_ctx: WW mutex context pointer
* @state: The task state for sleeping
*/
static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state)
{
unsigned long flags;
int ret;
/*
* Do all pre-schedule work here, before we queue a waiter and invoke
* PI -- any such work that trips on rtlock (PREEMPT_RT spinlock) would
* otherwise recurse back into task_blocks_on_rt_mutex() through
* rtlock_slowlock() and will then enqueue a second waiter for this
* same task and things get really confusing real fast.
*/
rt_mutex_pre_schedule();
/*
* Technically we could use raw_spin_[un]lock_irq() here, but this can
* be called in early boot if the cmpxchg() fast path is disabled
* (debug, no architecture support). In this case we will acquire the
* rtmutex with lock->wait_lock held. But we cannot unconditionally
* enable interrupts in that early boot case. So we need to use the
* irqsave/restore variants.
*/
raw_spin_lock_irqsave(&lock->wait_lock, flags);
ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
rt_mutex_post_schedule();
return ret;
}
static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
unsigned int state)
{
lockdep_assert(!current->pi_blocked_on);
if (likely(rt_mutex_try_acquire(lock)))
return 0;
return rt_mutex_slowlock(lock, NULL, state);
}
#endif /* RT_MUTEX_BUILD_MUTEX */
#ifdef RT_MUTEX_BUILD_SPINLOCKS
/*
* Functions required for spin/rw_lock substitution on RT kernels
*/
/**
* rtlock_slowlock_locked - Slow path lock acquisition for RT locks
* @lock: The underlying RT mutex
*/
static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
{
struct rt_mutex_waiter waiter;
struct task_struct *owner;
lockdep_assert_held(&lock->wait_lock);
if (try_to_take_rt_mutex(lock, current, NULL))
return;
rt_mutex_init_rtlock_waiter(&waiter);
/* Save current state and set state to TASK_RTLOCK_WAIT */
current_save_and_set_rtlock_wait_state();
trace_contention_begin(lock, LCB_F_RT);
task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
for (;;) {
/* Try to acquire the lock again */
if (try_to_take_rt_mutex(lock, current, &waiter))
break;
if (&waiter == rt_mutex_top_waiter(lock))
owner = rt_mutex_owner(lock);
else
owner = NULL;
raw_spin_unlock_irq(&lock->wait_lock);
if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
schedule_rtlock();
raw_spin_lock_irq(&lock->wait_lock);
set_current_state(TASK_RTLOCK_WAIT);
}
/* Restore the task state */
current_restore_rtlock_saved_state();
/*
* try_to_take_rt_mutex() sets the waiter bit unconditionally.
* We might have to fix that up:
*/
fixup_rt_mutex_waiters(lock, true);
debug_rt_mutex_free_waiter(&waiter);
trace_contention_end(lock, 0);
}
static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
{
unsigned long flags;
raw_spin_lock_irqsave(&lock->wait_lock, flags);
rtlock_slowlock_locked(lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
}
#endif /* RT_MUTEX_BUILD_SPINLOCKS */
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