// SPDX-License-Identifier: GPL-2.0+
/*
* Sleepable Read-Copy Update mechanism for mutual exclusion.
*
* Copyright (C) IBM Corporation, 2006
* Copyright (C) Fujitsu, 2012
*
* Authors: Paul McKenney <[email protected]>
* Lai Jiangshan <[email protected]>
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU/ *.txt
*
*/
#define pr_fmt(fmt) "rcu: " fmt
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate_wait.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/srcu.h>
#include "rcu.h"
#include "rcu_segcblist.h"
/* Holdoff in nanoseconds for auto-expediting. */
#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
module_param(exp_holdoff, ulong, 0444);
/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */
static ulong counter_wrap_check = (ULONG_MAX >> 2);
module_param(counter_wrap_check, ulong, 0444);
/*
* Control conversion to SRCU_SIZE_BIG:
* 0: Don't convert at all.
* 1: Convert at init_srcu_struct() time.
* 2: Convert when rcutorture invokes srcu_torture_stats_print().
* 3: Decide at boot time based on system shape (default).
* 0x1x: Convert when excessive contention encountered.
*/
#define SRCU_SIZING_NONE 0
#define SRCU_SIZING_INIT 1
#define SRCU_SIZING_TORTURE 2
#define SRCU_SIZING_AUTO 3
#define SRCU_SIZING_CONTEND 0x10
#define SRCU_SIZING_IS(x) ((convert_to_big & ~SRCU_SIZING_CONTEND) == x)
#define SRCU_SIZING_IS_NONE() (SRCU_SIZING_IS(SRCU_SIZING_NONE))
#define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT))
#define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE))
#define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND)
static int convert_to_big = SRCU_SIZING_AUTO;
module_param(convert_to_big, int, 0444);
/* Number of CPUs to trigger init_srcu_struct()-time transition to big. */
static int big_cpu_lim __read_mostly = 128;
module_param(big_cpu_lim, int, 0444);
/* Contention events per jiffy to initiate transition to big. */
static int small_contention_lim __read_mostly = 100;
module_param(small_contention_lim, int, 0444);
/* Early-boot callback-management, so early that no lock is required! */
static LIST_HEAD(srcu_boot_list);
static bool __read_mostly srcu_init_done;
static void srcu_invoke_callbacks(struct work_struct *work);
static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
static void process_srcu(struct work_struct *work);
static void srcu_delay_timer(struct timer_list *t);
/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
#define spin_lock_rcu_node(p) \
do { \
spin_lock(&ACCESS_PRIVATE(p, lock)); \
smp_mb__after_unlock_lock(); \
} while (0)
#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock))
#define spin_lock_irq_rcu_node(p) \
do { \
spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \
smp_mb__after_unlock_lock(); \
} while (0)
#define spin_unlock_irq_rcu_node(p) \
spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
#define spin_lock_irqsave_rcu_node(p, flags) \
do { \
spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
smp_mb__after_unlock_lock(); \
} while (0)
#define spin_trylock_irqsave_rcu_node(p, flags) \
({ \
bool ___locked = spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \
\
if (___locked) \
smp_mb__after_unlock_lock(); \
___locked; \
})
#define spin_unlock_irqrestore_rcu_node(p, flags) \
spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \
/*
* Initialize SRCU per-CPU data. Note that statically allocated
* srcu_struct structures might already have srcu_read_lock() and
* srcu_read_unlock() running against them. So if the is_static parameter
* is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
*/
static void init_srcu_struct_data(struct srcu_struct *ssp)
{
int cpu;
struct srcu_data *sdp;
/*
* Initialize the per-CPU srcu_data array, which feeds into the
* leaves of the srcu_node tree.
*/
WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
ARRAY_SIZE(sdp->srcu_unlock_count));
for_each_possible_cpu(cpu) {
sdp = per_cpu_ptr(ssp->sda, cpu);
spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
rcu_segcblist_init(&sdp->srcu_cblist);
sdp->srcu_cblist_invoking = false;
sdp->srcu_gp_seq_needed = ssp->srcu_sup->srcu_gp_seq;
sdp->srcu_gp_seq_needed_exp = ssp->srcu_sup->srcu_gp_seq;
sdp->srcu_barrier_head.next = &sdp->srcu_barrier_head;
sdp->mynode = NULL;
sdp->cpu = cpu;
INIT_WORK(&sdp->work, srcu_invoke_callbacks);
timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
sdp->ssp = ssp;
}
}
/* Invalid seq state, used during snp node initialization */
#define SRCU_SNP_INIT_SEQ 0x2
/*
* Check whether sequence number corresponding to snp node,
* is invalid.
*/
static inline bool srcu_invl_snp_seq(unsigned long s)
{
return s == SRCU_SNP_INIT_SEQ;
}
/*
* Allocated and initialize SRCU combining tree. Returns @true if
* allocation succeeded and @false otherwise.
*/
static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
{
int cpu;
int i;
int level = 0;
int levelspread[RCU_NUM_LVLS];
struct srcu_data *sdp;
struct srcu_node *snp;
struct srcu_node *snp_first;
/* Initialize geometry if it has not already been initialized. */
rcu_init_geometry();
ssp->srcu_sup->node = kcalloc(rcu_num_nodes, sizeof(*ssp->srcu_sup->node), gfp_flags);
if (!ssp->srcu_sup->node)
return false;
/* Work out the overall tree geometry. */
ssp->srcu_sup->level[0] = &ssp->srcu_sup->node[0];
for (i = 1; i < rcu_num_lvls; i++)
ssp->srcu_sup->level[i] = ssp->srcu_sup->level[i - 1] + num_rcu_lvl[i - 1];
rcu_init_levelspread(levelspread, num_rcu_lvl);
/* Each pass through this loop initializes one srcu_node structure. */
srcu_for_each_node_breadth_first(ssp, snp) {
spin_lock_init(&ACCESS_PRIVATE(snp, lock));
WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
ARRAY_SIZE(snp->srcu_data_have_cbs));
for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
snp->srcu_have_cbs[i] = SRCU_SNP_INIT_SEQ;
snp->srcu_data_have_cbs[i] = 0;
}
snp->srcu_gp_seq_needed_exp = SRCU_SNP_INIT_SEQ;
snp->grplo = -1;
snp->grphi = -1;
if (snp == &ssp->srcu_sup->node[0]) {
/* Root node, special case. */
snp->srcu_parent = NULL;
continue;
}
/* Non-root node. */
if (snp == ssp->srcu_sup->level[level + 1])
level++;
snp->srcu_parent = ssp->srcu_sup->level[level - 1] +
(snp - ssp->srcu_sup->level[level]) /
levelspread[level - 1];
}
/*
* Initialize the per-CPU srcu_data array, which feeds into the
* leaves of the srcu_node tree.
*/
level = rcu_num_lvls - 1;
snp_first = ssp->srcu_sup->level[level];
for_each_possible_cpu(cpu) {
sdp = per_cpu_ptr(ssp->sda, cpu);
sdp->mynode = &snp_first[cpu / levelspread[level]];
for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
if (snp->grplo < 0)
snp->grplo = cpu;
snp->grphi = cpu;
}
sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
}
smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
return true;
}
/*
* Initialize non-compile-time initialized fields, including the
* associated srcu_node and srcu_data structures. The is_static parameter
* tells us that ->sda has already been wired up to srcu_data.
*/
static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
{
if (!is_static)
ssp->srcu_sup = kzalloc(sizeof(*ssp->srcu_sup), GFP_KERNEL);
if (!ssp->srcu_sup)
return -ENOMEM;
if (!is_static)
spin_lock_init(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
ssp->srcu_sup->srcu_size_state = SRCU_SIZE_SMALL;
ssp->srcu_sup->node = NULL;
mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
ssp->srcu_idx = 0;
ssp->srcu_sup->srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL;
ssp->srcu_sup->srcu_barrier_seq = 0;
mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu);
ssp->srcu_sup->sda_is_static = is_static;
if (!is_static)
ssp->sda = alloc_percpu(struct srcu_data);
if (!ssp->sda)
goto err_free_sup;
init_srcu_struct_data(ssp);
ssp->srcu_sup->srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL;
ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
goto err_free_sda;
WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
}
ssp->srcu_sup->srcu_ssp = ssp;
smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed,
SRCU_GP_SEQ_INITIAL_VAL); /* Init done. */
return 0;
err_free_sda:
if (!is_static) {
free_percpu(ssp->sda);
ssp->sda = NULL;
}
err_free_sup:
if (!is_static) {
kfree(ssp->srcu_sup);
ssp->srcu_sup = NULL;
}
return -ENOMEM;
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
struct lock_class_key *key)
{
/* Don't re-initialize a lock while it is held. */
debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
lockdep_init_map(&ssp->dep_map, name, key, 0);
return init_srcu_struct_fields(ssp, false);
}
EXPORT_SYMBOL_GPL(__init_srcu_struct);
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/**
* init_srcu_struct - initialize a sleep-RCU structure
* @ssp: structure to initialize.
*
* Must invoke this on a given srcu_struct before passing that srcu_struct
* to any other function. Each srcu_struct represents a separate domain
* of SRCU protection.
*/
int init_srcu_struct(struct srcu_struct *ssp)
{
return init_srcu_struct_fields(ssp, false);
}
EXPORT_SYMBOL_GPL(init_srcu_struct);
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/*
* Initiate a transition to SRCU_SIZE_BIG with lock held.
*/
static void __srcu_transition_to_big(struct srcu_struct *ssp)
{
lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_ALLOC);
}
/*
* Initiate an idempotent transition to SRCU_SIZE_BIG.
*/
static void srcu_transition_to_big(struct srcu_struct *ssp)
{
unsigned long flags;
/* Double-checked locking on ->srcu_size-state. */
if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL)
return;
spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags);
if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL) {
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
return;
}
__srcu_transition_to_big(ssp);
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
}
/*
* Check to see if the just-encountered contention event justifies
* a transition to SRCU_SIZE_BIG.
*/
static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp)
{
unsigned long j;
if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_sup->srcu_size_state)
return;
j = jiffies;
if (ssp->srcu_sup->srcu_size_jiffies != j) {
ssp->srcu_sup->srcu_size_jiffies = j;
ssp->srcu_sup->srcu_n_lock_retries = 0;
}
if (++ssp->srcu_sup->srcu_n_lock_retries <= small_contention_lim)
return;
__srcu_transition_to_big(ssp);
}
/*
* Acquire the specified srcu_data structure's ->lock, but check for
* excessive contention, which results in initiation of a transition
* to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module
* parameter permits this.
*/
static void spin_lock_irqsave_sdp_contention(struct srcu_data *sdp, unsigned long *flags)
{
struct srcu_struct *ssp = sdp->ssp;
if (spin_trylock_irqsave_rcu_node(sdp, *flags))
return;
spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags);
spin_lock_irqsave_check_contention(ssp);
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, *flags);
spin_lock_irqsave_rcu_node(sdp, *flags);
}
/*
* Acquire the specified srcu_struct structure's ->lock, but check for
* excessive contention, which results in initiation of a transition
* to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module
* parameter permits this.
*/
static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags)
{
if (spin_trylock_irqsave_rcu_node(ssp->srcu_sup, *flags))
return;
spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags);
spin_lock_irqsave_check_contention(ssp);
}
/*
* First-use initialization of statically allocated srcu_struct
* structure. Wiring up the combining tree is more than can be
* done with compile-time initialization, so this check is added
* to each update-side SRCU primitive. Use ssp->lock, which -is-
* compile-time initialized, to resolve races involving multiple
* CPUs trying to garner first-use privileges.
*/
static void check_init_srcu_struct(struct srcu_struct *ssp)
{
unsigned long flags;
/* The smp_load_acquire() pairs with the smp_store_release(). */
if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed))) /*^^^*/
return; /* Already initialized. */
spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags);
if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq_needed)) {
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
return;
}
init_srcu_struct_fields(ssp, true);
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
}
/*
* Returns approximate total of the readers' ->srcu_lock_count[] values
* for the rank of per-CPU counters specified by idx.
*/
static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
{
int cpu;
unsigned long sum = 0;
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += atomic_long_read(&cpuc->srcu_lock_count[idx]);
}
return sum;
}
/*
* Returns approximate total of the readers' ->srcu_unlock_count[] values
* for the rank of per-CPU counters specified by idx.
*/
static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
{
int cpu;
unsigned long mask = 0;
unsigned long sum = 0;
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]);
if (IS_ENABLED(CONFIG_PROVE_RCU))
mask = mask | READ_ONCE(cpuc->srcu_nmi_safety);
}
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)),
"Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
return sum;
}
/*
* Return true if the number of pre-existing readers is determined to
* be zero.
*/
static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
{
unsigned long unlocks;
unlocks = srcu_readers_unlock_idx(ssp, idx);
/*
* Make sure that a lock is always counted if the corresponding
* unlock is counted. Needs to be a smp_mb() as the read side may
* contain a read from a variable that is written to before the
* synchronize_srcu() in the write side. In this case smp_mb()s
* A and B act like the store buffering pattern.
*
* This smp_mb() also pairs with smp_mb() C to prevent accesses
* after the synchronize_srcu() from being executed before the
* grace period ends.
*/
smp_mb(); /* A */
/*
* If the locks are the same as the unlocks, then there must have
* been no readers on this index at some point in this function.
* But there might be more readers, as a task might have read
* the current ->srcu_idx but not yet have incremented its CPU's
* ->srcu_lock_count[idx] counter. In fact, it is possible
* that most of the tasks have been preempted between fetching
* ->srcu_idx and incrementing ->srcu_lock_count[idx]. And there
* could be almost (ULONG_MAX / sizeof(struct task_struct)) tasks
* in a system whose address space was fully populated with memory.
* Call this quantity Nt.
*
* So suppose that the updater is preempted at this point in the
* code for a long time. That now-preempted updater has already
* flipped ->srcu_idx (possibly during the preceding grace period),
* done an smp_mb() (again, possibly during the preceding grace
* period), and summed up the ->srcu_unlock_count[idx] counters.
* How many times can a given one of the aforementioned Nt tasks
* increment the old ->srcu_idx value's ->srcu_lock_count[idx]
* counter, in the absence of nesting?
*
* It can clearly do so once, given that it has already fetched
* the old value of ->srcu_idx and is just about to use that value
* to index its increment of ->srcu_lock_count[idx]. But as soon as
* it leaves that SRCU read-side critical section, it will increment
* ->srcu_unlock_count[idx], which must follow the updater's above
* read from that same value. Thus, as soon the reading task does
* an smp_mb() and a later fetch from ->srcu_idx, that task will be
* guaranteed to get the new index. Except that the increment of
* ->srcu_unlock_count[idx] in __srcu_read_unlock() is after the
* smp_mb(), and the fetch from ->srcu_idx in __srcu_read_lock()
* is before the smp_mb(). Thus, that task might not see the new
* value of ->srcu_idx until the -second- __srcu_read_lock(),
* which in turn means that this task might well increment
* ->srcu_lock_count[idx] for the old value of ->srcu_idx twice,
* not just once.
*
* However, it is important to note that a given smp_mb() takes
* effect not just for the task executing it, but also for any
* later task running on that same CPU.
*
* That is, there can be almost Nt + Nc further increments of
* ->srcu_lock_count[idx] for the old index, where Nc is the number
* of CPUs. But this is OK because the size of the task_struct
* structure limits the value of Nt and current systems limit Nc
* to a few thousand.
*
* OK, but what about nesting? This does impose a limit on
* nesting of half of the size of the task_struct structure
* (measured in bytes), which should be sufficient. A late 2022
* TREE01 rcutorture run reported this size to be no less than
* 9408 bytes, allowing up to 4704 levels of nesting, which is
* comfortably beyond excessive. Especially on 64-bit systems,
* which are unlikely to be configured with an address space fully
* populated with memory, at least not anytime soon.
*/
return srcu_readers_lock_idx(ssp, idx) == unlocks;
}
/**
* srcu_readers_active - returns true if there are readers. and false
* otherwise
* @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
*
* Note that this is not an atomic primitive, and can therefore suffer
* severe errors when invoked on an active srcu_struct. That said, it
* can be useful as an error check at cleanup time.
*/
static bool srcu_readers_active(struct srcu_struct *ssp)
{
int cpu;
unsigned long sum = 0;
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += atomic_long_read(&cpuc->srcu_lock_count[0]);
sum += atomic_long_read(&cpuc->srcu_lock_count[1]);
sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]);
sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]);
}
return sum;
}
/*
* We use an adaptive strategy for synchronize_srcu() and especially for
* synchronize_srcu_expedited(). We spin for a fixed time period
* (defined below, boot time configurable) to allow SRCU readers to exit
* their read-side critical sections. If there are still some readers
* after one jiffy, we repeatedly block for one jiffy time periods.
* The blocking time is increased as the grace-period age increases,
* with max blocking time capped at 10 jiffies.
*/
#define SRCU_DEFAULT_RETRY_CHECK_DELAY 5
static ulong srcu_retry_check_delay = SRCU_DEFAULT_RETRY_CHECK_DELAY;
module_param(srcu_retry_check_delay, ulong, 0444);
#define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending.
#define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers.
#define SRCU_DEFAULT_MAX_NODELAY_PHASE_LO 3UL // Lowmark on default per-GP-phase
// no-delay instances.
#define SRCU_DEFAULT_MAX_NODELAY_PHASE_HI 1000UL // Highmark on default per-GP-phase
// no-delay instances.
#define SRCU_UL_CLAMP_LO(val, low) ((val) > (low) ? (val) : (low))
#define SRCU_UL_CLAMP_HI(val, high) ((val) < (high) ? (val) : (high))
#define SRCU_UL_CLAMP(val, low, high) SRCU_UL_CLAMP_HI(SRCU_UL_CLAMP_LO((val), (low)), (high))
// per-GP-phase no-delay instances adjusted to allow non-sleeping poll upto
// one jiffies time duration. Mult by 2 is done to factor in the srcu_get_delay()
// called from process_srcu().
#define SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED \
(2UL * USEC_PER_SEC / HZ / SRCU_DEFAULT_RETRY_CHECK_DELAY)
// Maximum per-GP-phase consecutive no-delay instances.
#define SRCU_DEFAULT_MAX_NODELAY_PHASE \
SRCU_UL_CLAMP(SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED, \
SRCU_DEFAULT_MAX_NODELAY_PHASE_LO, \
SRCU_DEFAULT_MAX_NODELAY_PHASE_HI)
static ulong srcu_max_nodelay_phase = SRCU_DEFAULT_MAX_NODELAY_PHASE;
module_param(srcu_max_nodelay_phase, ulong, 0444);
// Maximum consecutive no-delay instances.
#define SRCU_DEFAULT_MAX_NODELAY (SRCU_DEFAULT_MAX_NODELAY_PHASE > 100 ? \
SRCU_DEFAULT_MAX_NODELAY_PHASE : 100)
static ulong srcu_max_nodelay = SRCU_DEFAULT_MAX_NODELAY;
module_param(srcu_max_nodelay, ulong, 0444);
/*
* Return grace-period delay, zero if there are expedited grace
* periods pending, SRCU_INTERVAL otherwise.
*/
static unsigned long srcu_get_delay(struct srcu_struct *ssp)
{
unsigned long gpstart;
unsigned long j;
unsigned long jbase = SRCU_INTERVAL;
struct srcu_usage *sup = ssp->srcu_sup;
if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp)))
jbase = 0;
if (rcu_seq_state(READ_ONCE(sup->srcu_gp_seq))) {
j = jiffies - 1;
gpstart = READ_ONCE(sup->srcu_gp_start);
if (time_after(j, gpstart))
jbase += j - gpstart;
if (!jbase) {
ASSERT_EXCLUSIVE_WRITER(sup->srcu_n_exp_nodelay);
WRITE_ONCE(sup->srcu_n_exp_nodelay, READ_ONCE(sup->srcu_n_exp_nodelay) + 1);
if (READ_ONCE(sup->srcu_n_exp_nodelay) > srcu_max_nodelay_phase)
jbase = 1;
}
}
return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase;
}
/**
* cleanup_srcu_struct - deconstruct a sleep-RCU structure
* @ssp: structure to clean up.
*
* Must invoke this after you are finished using a given srcu_struct that
* was initialized via init_srcu_struct(), else you leak memory.
*/
void cleanup_srcu_struct(struct srcu_struct *ssp)
{
int cpu;
struct srcu_usage *sup = ssp->srcu_sup;
if (WARN_ON(!srcu_get_delay(ssp)))
return; /* Just leak it! */
if (WARN_ON(srcu_readers_active(ssp)))
return; /* Just leak it! */
flush_delayed_work(&sup->work);
for_each_possible_cpu(cpu) {
struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
del_timer_sync(&sdp->delay_work);
flush_work(&sdp->work);
if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
return; /* Forgot srcu_barrier(), so just leak it! */
}
if (WARN_ON(rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
WARN_ON(rcu_seq_current(&sup->srcu_gp_seq) != sup->srcu_gp_seq_needed) ||
WARN_ON(srcu_readers_active(ssp))) {
pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n",
__func__, ssp, rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)),
rcu_seq_current(&sup->srcu_gp_seq), sup->srcu_gp_seq_needed);
return; // Caller forgot to stop doing call_srcu()?
// Or caller invoked start_poll_synchronize_srcu()
// and then cleanup_srcu_struct() before that grace
// period ended?
}
kfree(sup->node);
sup->node = NULL;
sup->srcu_size_state = SRCU_SIZE_SMALL;
if (!sup->sda_is_static) {
free_percpu(ssp->sda);
ssp->sda = NULL;
kfree(sup);
ssp->srcu_sup = NULL;
}
}
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
#ifdef CONFIG_PROVE_RCU
/*
* Check for consistent NMI safety.
*/
void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe)
{
int nmi_safe_mask = 1 << nmi_safe;
int old_nmi_safe_mask;
struct srcu_data *sdp;
/* NMI-unsafe use in NMI is a bad sign */
WARN_ON_ONCE(!nmi_safe && in_nmi());
sdp = raw_cpu_ptr(ssp->sda);
old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety);
if (!old_nmi_safe_mask) {
WRITE_ONCE(sdp->srcu_nmi_safety, nmi_safe_mask);
return;
}
WARN_ONCE(old_nmi_safe_mask != nmi_safe_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_nmi_safe_mask, nmi_safe_mask);
}
EXPORT_SYMBOL_GPL(srcu_check_nmi_safety);
#endif /* CONFIG_PROVE_RCU */
/*
* Counts the new reader in the appropriate per-CPU element of the
* srcu_struct.
* Returns an index that must be passed to the matching srcu_read_unlock().
*/
int __srcu_read_lock(struct srcu_struct *ssp)
{
int idx;
idx = READ_ONCE(ssp->srcu_idx) & 0x1;
this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
smp_mb(); /* B */ /* Avoid leaking the critical section. */
return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock);
/*
* Removes the count for the old reader from the appropriate per-CPU
* element of the srcu_struct. Note that this may well be a different
* CPU than that which was incremented by the corresponding srcu_read_lock().
*/
void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
{
smp_mb(); /* C */ /* Avoid leaking the critical section. */
this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
#ifdef CONFIG_NEED_SRCU_NMI_SAFE
/*
* Counts the new reader in the appropriate per-CPU element of the
* srcu_struct, but in an NMI-safe manner using RMW atomics.
* Returns an index that must be passed to the matching srcu_read_unlock().
*/
int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
{
int idx;
struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
idx = READ_ONCE(ssp->srcu_idx) & 0x1;
atomic_long_inc(&sdp->srcu_lock_count[idx]);
smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */
return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
/*
* Removes the count for the old reader from the appropriate per-CPU
* element of the srcu_struct. Note that this may well be a different
* CPU than that which was incremented by the corresponding srcu_read_lock().
*/
void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
{
struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
smp_mb__before_atomic(); /* C */ /* Avoid leaking the critical section. */
atomic_long_inc(&sdp->srcu_unlock_count[idx]);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe);
#endif // CONFIG_NEED_SRCU_NMI_SAFE
/*
* Start an SRCU grace period.
*/
static void srcu_gp_start(struct srcu_struct *ssp)
{
int state;
lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed));
WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);
WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
rcu_seq_start(&ssp->srcu_sup->srcu_gp_seq);
state = rcu_seq_state(ssp->srcu_sup->srcu_gp_seq);
WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
}
static void srcu_delay_timer(struct timer_list *t)
{
struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
}
static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
unsigned long delay)
{
if (!delay) {
queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
return;
}
timer_reduce(&sdp->delay_work, jiffies + delay);
}
/*
* Schedule callback invocation for the specified srcu_data structure,
* if possible, on the corresponding CPU.
*/
static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
{
srcu_queue_delayed_work_on(sdp, delay);
}
/*
* Schedule callback invocation for all srcu_data structures associated
* with the specified srcu_node structure that have callbacks for the
* just-completed grace period, the one corresponding to idx. If possible,
* schedule this invocation on the corresponding CPUs.
*/
static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp,
unsigned long mask, unsigned long delay)
{
int cpu;
for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
if (!(mask & (1UL << (cpu - snp->grplo))))
continue;
srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
}
}
/*
* Note the end of an SRCU grace period. Initiates callback invocation
* and starts a new grace period if needed.
*
* The ->srcu_cb_mutex acquisition does not protect any data, but
* instead prevents more than one grace period from starting while we
* are initiating callback invocation. This allows the ->srcu_have_cbs[]
* array to have a finite number of elements.
*/
static void srcu_gp_end(struct srcu_struct *ssp)
{
unsigned long cbdelay = 1;
bool cbs;
bool last_lvl;
int cpu;
unsigned long gpseq;
int idx;
unsigned long mask;
struct srcu_data *sdp;
unsigned long sgsne;
struct srcu_node *snp;
int ss_state;
struct srcu_usage *sup = ssp->srcu_sup;
/* Prevent more than one additional grace period. */
mutex_lock(&sup->srcu_cb_mutex);
/* End the current grace period. */
spin_lock_irq_rcu_node(sup);
idx = rcu_seq_state(sup->srcu_gp_seq);
WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp)))
cbdelay = 0;
WRITE_ONCE(sup->srcu_last_gp_end, ktime_get_mono_fast_ns());
rcu_seq_end(&sup->srcu_gp_seq);
gpseq = rcu_seq_current(&sup->srcu_gp_seq);
if (ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, gpseq))
WRITE_ONCE(sup->srcu_gp_seq_needed_exp, gpseq);
spin_unlock_irq_rcu_node(sup);
mutex_unlock(&sup->srcu_gp_mutex);
/* A new grace period can start at this point. But only one. */
/* Initiate callback invocation as needed. */
ss_state = smp_load_acquire(&sup->srcu_size_state);
if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()),
cbdelay);
} else {
idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
srcu_for_each_node_breadth_first(ssp, snp) {
spin_lock_irq_rcu_node(snp);
cbs = false;
last_lvl = snp >= sup->level[rcu_num_lvls - 1];
if (last_lvl)
cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
snp->srcu_have_cbs[idx] = gpseq;
rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
sgsne = snp->srcu_gp_seq_needed_exp;
if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq))
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
if (ss_state < SRCU_SIZE_BIG)
mask = ~0;
else
mask = snp->srcu_data_have_cbs[idx];
snp->srcu_data_have_cbs[idx] = 0;
spin_unlock_irq_rcu_node(snp);
if (cbs)
srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay);
}
}
/* Occasionally prevent srcu_data counter wrap. */
if (!(gpseq & counter_wrap_check))
for_each_possible_cpu(cpu) {
sdp = per_cpu_ptr(ssp->sda, cpu);
spin_lock_irq_rcu_node(sdp);
if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed + 100))
sdp->srcu_gp_seq_needed = gpseq;
if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed_exp + 100))
sdp->srcu_gp_seq_needed_exp = gpseq;
spin_unlock_irq_rcu_node(sdp);
}
/* Callback initiation done, allow grace periods after next. */
mutex_unlock(&sup->srcu_cb_mutex);
/* Start a new grace period if needed. */
spin_lock_irq_rcu_node(sup);
gpseq = rcu_seq_current(&sup->srcu_gp_seq);
if (!rcu_seq_state(gpseq) &&
ULONG_CMP_LT(gpseq, sup->srcu_gp_seq_needed)) {
srcu_gp_start(ssp);
spin_unlock_irq_rcu_node(sup);
srcu_reschedule(ssp, 0);
} else {
spin_unlock_irq_rcu_node(sup);
}
/* Transition to big if needed. */
if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
if (ss_state == SRCU_SIZE_ALLOC)
init_srcu_struct_nodes(ssp, GFP_KERNEL);
else
smp_store_release(&sup->srcu_size_state, ss_state + 1);
}
}
/*
* Funnel-locking scheme to scalably mediate many concurrent expedited
* grace-period requests. This function is invoked for the first known
* expedited request for a grace period that has already been requested,
* but without expediting. To start a completely new grace period,
* whether expedited or not, use srcu_funnel_gp_start() instead.
*/
static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp,
unsigned long s)
{
unsigned long flags;
unsigned long sgsne;
if (snp)
for (; snp != NULL; snp = snp->srcu_parent) {
sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp);
if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, s)) ||
(!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)))
return;
spin_lock_irqsave_rcu_node(snp, flags);
sgsne = snp->srcu_gp_seq_needed_exp;
if (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)) {
spin_unlock_irqrestore_rcu_node(snp, flags);
return;
}
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
spin_unlock_irqrestore_rcu_node(snp, flags);
}
spin_lock_irqsave_ssp_contention(ssp, &flags);
if (ULONG_CMP_LT(ssp->srcu_sup->srcu_gp_seq_needed_exp, s))
WRITE_ONCE(ssp->srcu_sup->srcu_gp_seq_needed_exp, s);
spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags);
}
/*
* Funnel-locking scheme to scalably mediate many concurrent grace-period
* requests. The winner has to do the work of actually starting grace
* period s. Losers must either ensure that their desired grace-period
* number is recorded on at least their leaf srcu_node structure, or they
* must take steps to invoke their own callbacks.
*
* Note that this function also does the work of srcu_funnel_exp_start(),
* in some cases by directly invoking it.
*
* The srcu read lock should be hold around this function. And s is a seq snap
* after holding that lock.
*/
static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
unsigned long s, bool do_norm)
{
unsigned long flags;
int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
unsigned long sgsne;
struct srcu_node *snp;
struct srcu_node *snp_leaf;
unsigned long snp_seq;
struct srcu_usage *sup = ssp->srcu_sup;
/* Ensure that snp node tree is fully initialized before traversing it */
if (smp_load_acquire(&sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
snp_leaf = NULL;
else
snp_leaf = sdp->mynode;
if (snp_leaf)
/* Each pass through the loop does one level of the srcu_node tree. */
for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
if (WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) && snp != snp_leaf)
return; /* GP already done and CBs recorded. */
spin_lock_irqsave_rcu_node(snp, flags);
snp_seq = snp->srcu_have_cbs[idx];
if (!srcu_invl_snp_seq(snp_seq) && ULONG_CMP_GE(snp_seq, s)) {
if (snp == snp_leaf && snp_seq == s)
snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
spin_unlock_irqrestore_rcu_node(snp, flags);
if (snp == snp_leaf && snp_seq != s) {
srcu_schedule_cbs_sdp(sdp, do_norm ? SRCU_INTERVAL : 0);
return;
}
if (!do_norm)
srcu_funnel_exp_start(ssp, snp, s);
return;
}
snp->srcu_have_cbs[idx] = s;
if (snp == snp_leaf)
snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
sgsne = snp->srcu_gp_seq_needed_exp;
if (!do_norm && (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, s)))
WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
spin_unlock_irqrestore_rcu_node(snp, flags);
}
/* Top of tree, must ensure the grace period will be started. */
spin_lock_irqsave_ssp_contention(ssp, &flags);
if (ULONG_CMP_LT(sup->srcu_gp_seq_needed, s)) {
/*
* Record need for grace period s. Pair with load
* acquire setting up for initialization.
*/
smp_store_release(&sup->srcu_gp_seq_needed, s); /*^^^*/
}
if (!do_norm && ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, s))
WRITE_ONCE(sup->srcu_gp_seq_needed_exp, s);
/* If grace period not already in progress, start it. */
if (!WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) &&
rcu_seq_state(sup->srcu_gp_seq) == SRCU_STATE_IDLE) {
WARN_ON_ONCE(ULONG_CMP_GE(sup->srcu_gp_seq, sup->srcu_gp_seq_needed));
srcu_gp_start(ssp);
// And how can that list_add() in the "else" clause
// possibly be safe for concurrent execution? Well,
// it isn't. And it does not have to be. After all, it
// can only be executed during early boot when there is only
// the one boot CPU running with interrupts still disabled.
if (likely(srcu_init_done))
queue_delayed_work(rcu_gp_wq, &sup->work,
!!srcu_get_delay(ssp));
else if (list_empty(&sup->work.work.entry))
list_add(&sup->work.work.entry, &srcu_boot_list);
}
spin_unlock_irqrestore_rcu_node(sup, flags);
}
/*
* Wait until all readers counted by array index idx complete, but
* loop an additional time if there is an expedited grace period pending.
* The caller must ensure that ->srcu_idx is not changed while checking.
*/
static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount)
{
unsigned long curdelay;
curdelay = !srcu_get_delay(ssp);
for (;;) {
if (srcu_readers_active_idx_check(ssp, idx))
return true;
if ((--trycount + curdelay) <= 0)
return false;
udelay(srcu_retry_check_delay);
}
}
/*
* Increment the ->srcu_idx counter so that future SRCU readers will
* use the other rank of the ->srcu_(un)lock_count[] arrays. This allows
* us to wait for pre-existing readers in a starvation-free manner.
*/
static void srcu_flip(struct srcu_struct *ssp)
{
/*
* Because the flip of ->srcu_idx is executed only if the
* preceding call to srcu_readers_active_idx_check() found that
* the ->srcu_unlock_count[] and ->srcu_lock_count[] sums matched
* and because that summing uses atomic_long_read(), there is
* ordering due to a control dependency between that summing and
* the WRITE_ONCE() in this call to srcu_flip(). This ordering
* ensures that if this updater saw a given reader's increment from
* __srcu_read_lock(), that reader was using a value of ->srcu_idx
* from before the previous call to srcu_flip(), which should be
* quite rare. This ordering thus helps forward progress because
* the grace period could otherwise be delayed by additional
* calls to __srcu_read_lock() using that old (soon to be new)
* value of ->srcu_idx.
*
* This sum-equality check and ordering also ensures that if
* a given call to __srcu_read_lock() uses the new value of
* ->srcu_idx, this updater's earlier scans cannot have seen
* that reader's increments, which is all to the good, because
* this grace period need not wait on that reader. After all,
* if those earlier scans had seen that reader, there would have
* been a sum mismatch and this code would not be reached.
*
* This means that the following smp_mb() is redundant, but
* it stays until either (1) Compilers learn about this sort of
* control dependency or (2) Some production workload running on
* a production system is unduly delayed by this slowpath smp_mb().
*/
smp_mb(); /* E */ /* Pairs with B and C. */
WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter.
/*
* Ensure that if the updater misses an __srcu_read_unlock()
* increment, that task's __srcu_read_lock() following its next
* __srcu_read_lock() or __srcu_read_unlock() will see the above
* counter update. Note that both this memory barrier and the
* one in srcu_readers_active_idx_check() provide the guarantee
* for __srcu_read_lock().
*/
smp_mb(); /* D */ /* Pairs with C. */
}
/*
* If SRCU is likely idle, return true, otherwise return false.
*
* Note that it is OK for several current from-idle requests for a new
* grace period from idle to specify expediting because they will all end
* up requesting the same grace period anyhow. So no loss.
*
* Note also that if any CPU (including the current one) is still invoking
* callbacks, this function will nevertheless say "idle". This is not
* ideal, but the overhead of checking all CPUs' callback lists is even
* less ideal, especially on large systems. Furthermore, the wakeup
* can happen before the callback is fully removed, so we have no choice
* but to accept this type of error.
*
* This function is also subject to counter-wrap errors, but let's face
* it, if this function was preempted for enough time for the counters
* to wrap, it really doesn't matter whether or not we expedite the grace
* period. The extra overhead of a needlessly expedited grace period is
* negligible when amortized over that time period, and the extra latency
* of a needlessly non-expedited grace period is similarly negligible.
*/
static bool srcu_might_be_idle(struct srcu_struct *ssp)
{
unsigned long curseq;
unsigned long flags;
struct srcu_data *sdp;
unsigned long t;
unsigned long tlast;
check_init_srcu_struct(ssp);
/* If the local srcu_data structure has callbacks, not idle. */
sdp = raw_cpu_ptr(ssp->sda);
spin_lock_irqsave_rcu_node(sdp, flags);
if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
spin_unlock_irqrestore_rcu_node(sdp, flags);
return false; /* Callbacks already present, so not idle. */
}
spin_unlock_irqrestore_rcu_node(sdp, flags);
/*
* No local callbacks, so probabilistically probe global state.
* Exact information would require acquiring locks, which would
* kill scalability, hence the probabilistic nature of the probe.
*/
/* First, see if enough time has passed since the last GP. */
t = ktime_get_mono_fast_ns();
tlast = READ_ONCE(ssp->srcu_sup->srcu_last_gp_end);
if (exp_holdoff == 0 ||
time_in_range_open(t, tlast, tlast + exp_holdoff))
return false; /* Too soon after last GP. */
/* Next, check for probable idleness. */
curseq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq);
smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */
if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_sup->srcu_gp_seq_needed)))
return false; /* Grace period in progress, so not idle. */
smp_mb(); /* Order ->srcu_gp_seq with prior access. */
if (curseq != rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq))
return false; /* GP # changed, so not idle. */
return true; /* With reasonable probability, idle! */
}
/*
* SRCU callback function to leak a callback.
*/
static void srcu_leak_callback(struct rcu_head *rhp)
{
}
/*
* Start an SRCU grace period, and also queue the callback if non-NULL.
*/
static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
struct rcu_head *rhp, bool do_norm)
{
unsigned long flags;
int idx;
bool needexp = false;
bool needgp = false;
unsigned long s;
struct srcu_data *sdp;
struct srcu_node *sdp_mynode;
int ss_state;
check_init_srcu_struct(ssp);
/*
* While starting a new grace period, make sure we are in an
* SRCU read-side critical section so that the grace-period
* sequence number cannot wrap around in the meantime.
*/
idx = __srcu_read_lock_nmisafe(ssp);
ss_state = smp_load_acquire(&ssp->srcu_sup->srcu_size_state);
if (ss_state < SRCU_SIZE_WAIT_CALL)
sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
else
sdp = raw_cpu_ptr(ssp->sda);
spin_lock_irqsave_sdp_contention(sdp, &flags);
if (rhp)
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
/*
* It's crucial to capture the snapshot 's' for acceleration before
* reading the current gp_seq that is used for advancing. This is
* essential because if the acceleration snapshot is taken after a
* failed advancement attempt, there's a risk that a grace period may
* conclude and a new one may start in the interim. If the snapshot is
* captured after this sequence of events, the acceleration snapshot 's'
* could be excessively advanced, leading to acceleration failure.
* In such a scenario, an 'acceleration leak' can occur, where new
* callbacks become indefinitely stuck in the RCU_NEXT_TAIL segment.
* Also note that encountering advancing failures is a normal
* occurrence when the grace period for RCU_WAIT_TAIL is in progress.
*
* To see this, consider the following events which occur if
* rcu_seq_snap() were to be called after advance:
*
* 1) The RCU_WAIT_TAIL segment has callbacks (gp_num = X + 4) and the
* RCU_NEXT_READY_TAIL also has callbacks (gp_num = X + 8).
*
* 2) The grace period for RCU_WAIT_TAIL is seen as started but not
* completed so rcu_seq_current() returns X + SRCU_STATE_SCAN1.
*
* 3) This value is passed to rcu_segcblist_advance() which can't move
* any segment forward and fails.
*
* 4) srcu_gp_start_if_needed() still proceeds with callback acceleration.
* But then the call to rcu_seq_snap() observes the grace period for the
* RCU_WAIT_TAIL segment as completed and the subsequent one for the
* RCU_NEXT_READY_TAIL segment as started (ie: X + 4 + SRCU_STATE_SCAN1)
* so it returns a snapshot of the next grace period, which is X + 12.
*
* 5) The value of X + 12 is passed to rcu_segcblist_accelerate() but the
* freshly enqueued callback in RCU_NEXT_TAIL can't move to
* RCU_NEXT_READY_TAIL which already has callbacks for a previous grace
* period (gp_num = X + 8). So acceleration fails.
*/
s = rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq);
if (rhp) {
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
/*
* Acceleration can never fail because the base current gp_seq
* used for acceleration is <= the value of gp_seq used for
* advancing. This means that RCU_NEXT_TAIL segment will
* always be able to be emptied by the acceleration into the
* RCU_NEXT_READY_TAIL or RCU_WAIT_TAIL segments.
*/
WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s));
}
if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
sdp->srcu_gp_seq_needed = s;
needgp = true;
}
if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
sdp->srcu_gp_seq_needed_exp = s;
needexp = true;
}
spin_unlock_irqrestore_rcu_node(sdp, flags);
/* Ensure that snp node tree is fully initialized before traversing it */
if (ss_state < SRCU_SIZE_WAIT_BARRIER)
sdp_mynode = NULL;
else
sdp_mynode = sdp->mynode;
if (needgp)
srcu_funnel_gp_start(ssp, sdp, s, do_norm);
else if (needexp)
srcu_funnel_exp_start(ssp, sdp_mynode, s);
__srcu_read_unlock_nmisafe(ssp, idx);
return s;
}
/*
* Enqueue an SRCU callback on the srcu_data structure associated with
* the current CPU and the specified srcu_struct structure, initiating
* grace-period processing if it is not already running.
*
* Note that all CPUs must agree that the grace period extended beyond
* all pre-existing SRCU read-side critical section. On systems with
* more than one CPU, this means that when "func()" is invoked, each CPU
* is guaranteed to have executed a full memory barrier since the end of
* its last corresponding SRCU read-side critical section whose beginning
* preceded the call to call_srcu(). It also means that each CPU executing
* an SRCU read-side critical section that continues beyond the start of
* "func()" must have executed a memory barrier after the call_srcu()
* but before the beginning of that SRCU read-side critical section.
* Note that these guarantees include CPUs that are offline, idle, or
* executing in user mode, as well as CPUs that are executing in the kernel.
*
* Furthermore, if CPU A invoked call_srcu() and CPU B invoked the
* resulting SRCU callback function "func()", then both CPU A and CPU
* B are guaranteed to execute a full memory barrier during the time
* interval between the call to call_srcu() and the invocation of "func()".
* This guarantee applies even if CPU A and CPU B are the same CPU (but
* again only if the system has more than one CPU).
*
* Of course, these guarantees apply only for invocations of call_srcu(),
* srcu_read_lock(), and srcu_read_unlock() that are all passed the same
* srcu_struct structure.
*/
static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm)
{
if (debug_rcu_head_queue(rhp)) {
/* Probable double call_srcu(), so leak the callback. */
WRITE_ONCE(rhp->func, srcu_leak_callback);
WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
return;
}
rhp->func = func;
(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
}
/**
* call_srcu() - Queue a callback for invocation after an SRCU grace period
* @ssp: srcu_struct in queue the callback
* @rhp: structure to be used for queueing the SRCU callback.
* @func: function to be invoked after the SRCU grace period
*
* The callback function will be invoked some time after a full SRCU
* grace period elapses, in other words after all pre-existing SRCU
* read-side critical sections have completed. However, the callback
* function might well execute concurrently with other SRCU read-side
* critical sections that started after call_srcu() was invoked. SRCU
* read-side critical sections are delimited by srcu_read_lock() and
* srcu_read_unlock(), and may be nested.
*
* The callback will be invoked from process context, but must nevertheless
* be fast and must not block.
*/
void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func)
{
__call_srcu(ssp, rhp, func, true);
}
EXPORT_SYMBOL_GPL(call_srcu);
/*
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
*/
static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
{
struct rcu_synchronize rcu;
srcu_lock_sync(&ssp->dep_map);
RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
return;
might_sleep();
check_init_srcu_struct(ssp);
init_completion(&rcu.completion);
init_rcu_head_on_stack(&rcu.head);
__call_srcu(ssp, &rcu.head, wakeme_after_rcu, do_norm);
wait_for_completion(&rcu.completion);
destroy_rcu_head_on_stack(&rcu.head);
/*
* Make sure that later code is ordered after the SRCU grace
* period. This pairs with the spin_lock_irq_rcu_node()
* in srcu_invoke_callbacks(). Unlike Tree RCU, this is needed
* because the current CPU might have been totally uninvolved with
* (and thus unordered against) that grace period.
*/
smp_mb();
}
/**
* synchronize_srcu_expedited - Brute-force SRCU grace period
* @ssp: srcu_struct with which to synchronize.
*
* Wait for an SRCU grace period to elapse, but be more aggressive about
* spinning rather than blocking when waiting.
*
* Note that synchronize_srcu_expedited() has the same deadlock and
* memory-ordering properties as does synchronize_srcu().
*/
void synchronize_srcu_expedited(struct srcu_struct *ssp)
{
__synchronize_srcu(ssp, rcu_gp_is_normal());
}
EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
/**
* synchronize_srcu - wait for prior SRCU read-side critical-section completion
* @ssp: srcu_struct with which to synchronize.
*
* Wait for the count to drain to zero of both indexes. To avoid the
* possible starvation of synchronize_srcu(), it waits for the count of
* the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
* and then flip the srcu_idx and wait for the count of the other index.
*
* Can block; must be called from process context.
*
* Note that it is illegal to call synchronize_srcu() from the corresponding
* SRCU read-side critical section; doing so will result in deadlock.
* However, it is perfectly legal to call synchronize_srcu() on one
* srcu_struct from some other srcu_struct's read-side critical section,
* as long as the resulting graph of srcu_structs is acyclic.
*
* There are memory-ordering constraints implied by synchronize_srcu().
* On systems with more than one CPU, when synchronize_srcu() returns,
* each CPU is guaranteed to have executed a full memory barrier since
* the end of its last corresponding SRCU read-side critical section
* whose beginning preceded the call to synchronize_srcu(). In addition,
* each CPU having an SRCU read-side critical section that extends beyond
* the return from synchronize_srcu() is guaranteed to have executed a
* full memory barrier after the beginning of synchronize_srcu() and before
* the beginning of that SRCU read-side critical section. Note that these
* guarantees include CPUs that are offline, idle, or executing in user mode,
* as well as CPUs that are executing in the kernel.
*
* Furthermore, if CPU A invoked synchronize_srcu(), which returned
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
* to have executed a full memory barrier during the execution of
* synchronize_srcu(). This guarantee applies even if CPU A and CPU B
* are the same CPU, but again only if the system has more than one CPU.
*
* Of course, these memory-ordering guarantees apply only when
* synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
* passed the same srcu_struct structure.
*
* Implementation of these memory-ordering guarantees is similar to
* that of synchronize_rcu().
*
* If SRCU is likely idle, expedite the first request. This semantic
* was provided by Classic SRCU, and is relied upon by its users, so TREE
* SRCU must also provide it. Note that detecting idleness is heuristic
* and subject to both false positives and negatives.
*/
void synchronize_srcu(struct srcu_struct *ssp)
{
if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
synchronize_srcu_expedited(ssp);
else
__synchronize_srcu(ssp, true);
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
/**
* get_state_synchronize_srcu - Provide an end-of-grace-period cookie
* @ssp: srcu_struct to provide cookie for.
*
* This function returns a cookie that can be passed to
* poll_state_synchronize_srcu(), which will return true if a full grace
* period has elapsed in the meantime. It is the caller's responsibility
* to make sure that grace period happens, for example, by invoking
* call_srcu() after return from get_state_synchronize_srcu().
*/
unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
{
// Any prior manipulation of SRCU-protected data must happen
// before the load from ->srcu_gp_seq.
smp_mb();
return rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
/**
* start_poll_synchronize_srcu - Provide cookie and start grace period
* @ssp: srcu_struct to provide cookie for.
*
* This function returns a cookie that can be passed to
* poll_state_synchronize_srcu(), which will return true if a full grace
* period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
* this function also ensures that any needed SRCU grace period will be
* started. This convenience does come at a cost in terms of CPU overhead.
*/
unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
{
return srcu_gp_start_if_needed(ssp, NULL, true);
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
/**
* poll_state_synchronize_srcu - Has cookie's grace period ended?
* @ssp: srcu_struct to provide cookie for.
* @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
*
* This function takes the cookie that was returned from either
* get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
* returns @true if an SRCU grace period elapsed since the time that the
* cookie was created.
*
* Because cookies are finite in size, wrapping/overflow is possible.
* This is more pronounced on 32-bit systems where cookies are 32 bits,
* where in theory wrapping could happen in about 14 hours assuming
* 25-microsecond expedited SRCU grace periods. However, a more likely
* overflow lower bound is on the order of 24 days in the case of
* one-millisecond SRCU grace periods. Of course, wrapping in a 64-bit
* system requires geologic timespans, as in more than seven million years
* even for expedited SRCU grace periods.
*
* Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems
* that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU. This uses
* a 16-bit cookie, which rcutorture routinely wraps in a matter of a
* few minutes. If this proves to be a problem, this counter will be
* expanded to the same size as for Tree SRCU.
*/
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
{
if (cookie != SRCU_GET_STATE_COMPLETED &&
!rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))
return false;
// Ensure that the end of the SRCU grace period happens before
// any subsequent code that the caller might execute.
smp_mb(); // ^^^
return true;
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
/*
* Callback function for srcu_barrier() use.
*/
static void srcu_barrier_cb(struct rcu_head *rhp)
{
struct srcu_data *sdp;
struct srcu_struct *ssp;
rhp->next = rhp; // Mark the callback as having been invoked.
sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
ssp = sdp->ssp;
if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt))
complete(&ssp->srcu_sup->srcu_barrier_completion);
}
/*
* Enqueue an srcu_barrier() callback on the specified srcu_data
* structure's ->cblist. but only if that ->cblist already has at least one
* callback enqueued. Note that if a CPU already has callbacks enqueue,
* it must have already registered the need for a future grace period,
* so all we need do is enqueue a callback that will use the same grace
* period as the last callback already in the queue.
*/
static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp)
{
spin_lock_irq_rcu_node(sdp);
atomic_inc(&ssp->srcu_sup->srcu_barrier_cpu_cnt);
sdp->srcu_barrier_head.func = srcu_barrier_cb;
debug_rcu_head_queue(&sdp->srcu_barrier_head);
if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
&sdp->srcu_barrier_head)) {
debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
atomic_dec(&ssp->srcu_sup->srcu_barrier_cpu_cnt);
}
spin_unlock_irq_rcu_node(sdp);
}
/**
* srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
* @ssp: srcu_struct on which to wait for in-flight callbacks.
*/
void srcu_barrier(struct srcu_struct *ssp)
{
int cpu;
int idx;
unsigned long s = rcu_seq_snap(&ssp->srcu_sup->srcu_barrier_seq);
check_init_srcu_struct(ssp);
mutex_lock(&ssp->srcu_sup->srcu_barrier_mutex);
if (rcu_seq_done(&ssp->srcu_sup->srcu_barrier_seq, s)) {
smp_mb(); /* Force ordering following return. */
mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex);
return; /* Someone else did our work for us. */
}
rcu_seq_start(&ssp->srcu_sup->srcu_barrier_seq);
init_completion(&ssp->srcu_sup->srcu_barrier_completion);
/* Initial count prevents reaching zero until all CBs are posted. */
atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 1);
idx = __srcu_read_lock_nmisafe(ssp);
if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, get_boot_cpu_id()));
else
for_each_possible_cpu(cpu)
srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
__srcu_read_unlock_nmisafe(ssp, idx);
/* Remove the initial count, at which point reaching zero can happen. */
if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt))
complete(&ssp->srcu_sup->srcu_barrier_completion);
wait_for_completion(&ssp->srcu_sup->srcu_barrier_completion);
rcu_seq_end(&ssp->srcu_sup->srcu_barrier_seq);
mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex);
}
EXPORT_SYMBOL_GPL(srcu_barrier);
/**
* srcu_batches_completed - return batches completed.
* @ssp: srcu_struct on which to report batch completion.
*
* Report the number of batches, correlated with, but not necessarily
* precisely the same as, the number of grace periods that have elapsed.
*/
unsigned long srcu_batches_completed(struct srcu_struct *ssp)
{
return READ_ONCE(ssp->srcu_idx);
}
EXPORT_SYMBOL_GPL(srcu_batches_completed);
/*
* Core SRCU state machine. Push state bits of ->srcu_gp_seq
* to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
* completed in that state.
*/
static void srcu_advance_state(struct srcu_struct *ssp)
{
int idx;
mutex_lock(&ssp->srcu_sup->srcu_gp_mutex);
/*
* Because readers might be delayed for an extended period after
* fetching ->srcu_idx for their index, at any point in time there
* might well be readers using both idx=0 and idx=1. We therefore
* need to wait for readers to clear from both index values before
* invoking a callback.
*
* The load-acquire ensures that we see the accesses performed
* by the prior grace period.
*/
idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq)); /* ^^^ */
if (idx == SRCU_STATE_IDLE) {
spin_lock_irq_rcu_node(ssp->srcu_sup);
if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) {
WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq));
spin_unlock_irq_rcu_node(ssp->srcu_sup);
mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return;
}
idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq));
if (idx == SRCU_STATE_IDLE)
srcu_gp_start(ssp);
spin_unlock_irq_rcu_node(ssp->srcu_sup);
if (idx != SRCU_STATE_IDLE) {
mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* Someone else started the grace period. */
}
}
if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
idx = 1 ^ (ssp->srcu_idx & 1);
if (!try_check_zero(ssp, idx, 1)) {
mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* readers present, retry later. */
}
srcu_flip(ssp);
spin_lock_irq_rcu_node(ssp->srcu_sup);
rcu_seq_set_state(&ssp->srcu_sup->srcu_gp_seq, SRCU_STATE_SCAN2);
ssp->srcu_sup->srcu_n_exp_nodelay = 0;
spin_unlock_irq_rcu_node(ssp->srcu_sup);
}
if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
/*
* SRCU read-side critical sections are normally short,
* so check at least twice in quick succession after a flip.
*/
idx = 1 ^ (ssp->srcu_idx & 1);
if (!try_check_zero(ssp, idx, 2)) {
mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* readers present, retry later. */
}
ssp->srcu_sup->srcu_n_exp_nodelay = 0;
srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */
}
}
/*
* Invoke a limited number of SRCU callbacks that have passed through
* their grace period. If there are more to do, SRCU will reschedule
* the workqueue. Note that needed memory barriers have been executed
* in this task's context by srcu_readers_active_idx_check().
*/
static void srcu_invoke_callbacks(struct work_struct *work)
{
long len;
bool more;
struct rcu_cblist ready_cbs;
struct rcu_head *rhp;
struct srcu_data *sdp;
struct srcu_struct *ssp;
sdp = container_of(work, struct srcu_data, work);
ssp = sdp->ssp;
rcu_cblist_init(&ready_cbs);
spin_lock_irq_rcu_node(sdp);
WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
/*
* Although this function is theoretically re-entrant, concurrent
* callbacks invocation is disallowed to avoid executing an SRCU barrier
* too early.
*/
if (sdp->srcu_cblist_invoking ||
!rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
spin_unlock_irq_rcu_node(sdp);
return; /* Someone else on the job or nothing to do. */
}
/* We are on the job! Extract and invoke ready callbacks. */
sdp->srcu_cblist_invoking = true;
rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
len = ready_cbs.len;
spin_unlock_irq_rcu_node(sdp);
rhp = rcu_cblist_dequeue(&ready_cbs);
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
debug_rcu_head_unqueue(rhp);
debug_rcu_head_callback(rhp);
local_bh_disable();
rhp->func(rhp);
local_bh_enable();
}
WARN_ON_ONCE(ready_cbs.len);
/*
* Update counts, accelerate new callbacks, and if needed,
* schedule another round of callback invocation.
*/
spin_lock_irq_rcu_node(sdp);
rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
sdp->srcu_cblist_invoking = false;
more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
spin_unlock_irq_rcu_node(sdp);
/* An SRCU barrier or callbacks from previous nesting work pending */
if (more)
srcu_schedule_cbs_sdp(sdp, 0);
}
/*
* Finished one round of SRCU grace period. Start another if there are
* more SRCU callbacks queued, otherwise put SRCU into not-running state.
*/
static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay)
{
bool pushgp = true;
spin_lock_irq_rcu_node(ssp->srcu_sup);
if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) {
if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq))) {
/* All requests fulfilled, time to go idle. */
pushgp = false;
}
} else if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)) {
/* Outstanding request and no GP. Start one. */
srcu_gp_start(ssp);
}
spin_unlock_irq_rcu_node(ssp->srcu_sup);
if (pushgp)
queue_delayed_work(rcu_gp_wq, &ssp->srcu_sup->work, delay);
}
/*
* This is the work-queue function that handles SRCU grace periods.
*/
static void process_srcu(struct work_struct *work)
{
unsigned long curdelay;
unsigned long j;
struct srcu_struct *ssp;
struct srcu_usage *sup;
sup = container_of(work, struct srcu_usage, work.work);
ssp = sup->srcu_ssp;
srcu_advance_state(ssp);
curdelay = srcu_get_delay(ssp);
if (curdelay) {
WRITE_ONCE(sup->reschedule_count, 0);
} else {
j = jiffies;
if (READ_ONCE(sup->reschedule_jiffies) == j) {
ASSERT_EXCLUSIVE_WRITER(sup->reschedule_count);
WRITE_ONCE(sup->reschedule_count, READ_ONCE(sup->reschedule_count) + 1);
if (READ_ONCE(sup->reschedule_count) > srcu_max_nodelay)
curdelay = 1;
} else {
WRITE_ONCE(sup->reschedule_count, 1);
WRITE_ONCE(sup->reschedule_jiffies, j);
}
}
srcu_reschedule(ssp, curdelay);
}
void srcutorture_get_gp_data(struct srcu_struct *ssp, int *flags,
unsigned long *gp_seq)
{
*flags = 0;
*gp_seq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq);
}
EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
static const char * const srcu_size_state_name[] = {
"SRCU_SIZE_SMALL",
"SRCU_SIZE_ALLOC",
"SRCU_SIZE_WAIT_BARRIER",
"SRCU_SIZE_WAIT_CALL",
"SRCU_SIZE_WAIT_CBS1",
"SRCU_SIZE_WAIT_CBS2",
"SRCU_SIZE_WAIT_CBS3",
"SRCU_SIZE_WAIT_CBS4",
"SRCU_SIZE_BIG",
"SRCU_SIZE_???",
};
void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
{
int cpu;
int idx;
unsigned long s0 = 0, s1 = 0;
int ss_state = READ_ONCE(ssp->srcu_sup->srcu_size_state);
int ss_state_idx = ss_state;
idx = ssp->srcu_idx & 0x1;
if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name))
ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1;
pr_alert("%s%s Tree SRCU g%ld state %d (%s)",
tt, tf, rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq), ss_state,
srcu_size_state_name[ss_state_idx]);
if (!ssp->sda) {
// Called after cleanup_srcu_struct(), perhaps.
pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n");
} else {
pr_cont(" per-CPU(idx=%d):", idx);
for_each_possible_cpu(cpu) {
unsigned long l0, l1;
unsigned long u0, u1;
long c0, c1;
struct srcu_data *sdp;
sdp = per_cpu_ptr(ssp->sda, cpu);
u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx]));
u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx]));
/*
* Make sure that a lock is always counted if the corresponding
* unlock is counted.
*/
smp_rmb();
l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx]));
l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx]));
c0 = l0 - u0;
c1 = l1 - u1;
pr_cont(" %d(%ld,%ld %c)",
cpu, c0, c1,
"C."[rcu_segcblist_empty(&sdp->srcu_cblist)]);
s0 += c0;
s1 += c1;
}
pr_cont(" T(%ld,%ld)\n", s0, s1);
}
if (SRCU_SIZING_IS_TORTURE())
srcu_transition_to_big(ssp);
}
EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
static int __init srcu_bootup_announce(void)
{
pr_info("Hierarchical SRCU implementation.\n");
if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF)
pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff);
if (srcu_retry_check_delay != SRCU_DEFAULT_RETRY_CHECK_DELAY)
pr_info("\tNon-default retry check delay of %lu us.\n", srcu_retry_check_delay);
if (srcu_max_nodelay != SRCU_DEFAULT_MAX_NODELAY)
pr_info("\tNon-default max no-delay of %lu.\n", srcu_max_nodelay);
pr_info("\tMax phase no-delay instances is %lu.\n", srcu_max_nodelay_phase);
return 0;
}
early_initcall(srcu_bootup_announce);
void __init srcu_init(void)
{
struct srcu_usage *sup;
/* Decide on srcu_struct-size strategy. */
if (SRCU_SIZING_IS(SRCU_SIZING_AUTO)) {
if (nr_cpu_ids >= big_cpu_lim) {
convert_to_big = SRCU_SIZING_INIT; // Don't bother waiting for contention.
pr_info("%s: Setting srcu_struct sizes to big.\n", __func__);
} else {
convert_to_big = SRCU_SIZING_NONE | SRCU_SIZING_CONTEND;
pr_info("%s: Setting srcu_struct sizes based on contention.\n", __func__);
}
}
/*
* Once that is set, call_srcu() can follow the normal path and
* queue delayed work. This must follow RCU workqueues creation
* and timers initialization.
*/
srcu_init_done = true;
while (!list_empty(&srcu_boot_list)) {
sup = list_first_entry(&srcu_boot_list, struct srcu_usage,
work.work.entry);
list_del_init(&sup->work.work.entry);
if (SRCU_SIZING_IS(SRCU_SIZING_INIT) &&
sup->srcu_size_state == SRCU_SIZE_SMALL)
sup->srcu_size_state = SRCU_SIZE_ALLOC;
queue_work(rcu_gp_wq, &sup->work.work);
}
}
#ifdef CONFIG_MODULES
/* Initialize any global-scope srcu_struct structures used by this module. */
static int srcu_module_coming(struct module *mod)
{
int i;
struct srcu_struct *ssp;
struct srcu_struct **sspp = mod->srcu_struct_ptrs;
for (i = 0; i < mod->num_srcu_structs; i++) {
ssp = *(sspp++);
ssp->sda = alloc_percpu(struct srcu_data);
if (WARN_ON_ONCE(!ssp->sda))
return -ENOMEM;
}
return 0;
}
/* Clean up any global-scope srcu_struct structures used by this module. */
static void srcu_module_going(struct module *mod)
{
int i;
struct srcu_struct *ssp;
struct srcu_struct **sspp = mod->srcu_struct_ptrs;
for (i = 0; i < mod->num_srcu_structs; i++) {
ssp = *(sspp++);
if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed)) &&
!WARN_ON_ONCE(!ssp->srcu_sup->sda_is_static))
cleanup_srcu_struct(ssp);
if (!WARN_ON(srcu_readers_active(ssp)))
free_percpu(ssp->sda);
}
}
/* Handle one module, either coming or going. */
static int srcu_module_notify(struct notifier_block *self,
unsigned long val, void *data)
{
struct module *mod = data;
int ret = 0;
switch (val) {
case MODULE_STATE_COMING:
ret = srcu_module_coming(mod);
break;
case MODULE_STATE_GOING:
srcu_module_going(mod);
break;
default:
break;
}
return ret;
}
static struct notifier_block srcu_module_nb = {
.notifier_call = srcu_module_notify,
.priority = 0,
};
static __init int init_srcu_module_notifier(void)
{
int ret;
ret = register_module_notifier(&srcu_module_nb);
if (ret)
pr_warn("Failed to register srcu module notifier\n");
return ret;
}
late_initcall(init_srcu_module_notifier);
#endif /* #ifdef CONFIG_MODULES */
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