* Generic waiting primitives.
*
* (C) 2004 Nadia Yvette Chambers, Oracle
*/
#include "sched.h"
void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
{
spin_lock_init(&wq_head->lock);
lockdep_set_class_and_name(&wq_head->lock, key, name);
INIT_LIST_HEAD(&wq_head->head);
}
EXPORT_SYMBOL(__init_waitqueue_head);
void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{
unsigned long flags;
wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
__add_wait_queue(wq_head, wq_entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue);
void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{
unsigned long flags;
wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
__add_wait_queue_entry_tail(wq_head, wq_entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue_exclusive);
void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{
unsigned long flags;
spin_lock_irqsave(&wq_head->lock, flags);
__remove_wait_queue(wq_head, wq_entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(remove_wait_queue);
* Scan threshold to break wait queue walk.
* This allows a waker to take a break from holding the
* wait queue lock during the wait queue walk.
*/
#define WAITQUEUE_WALK_BREAK_CNT 64
* The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
* wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
* number) then we wake all the non-exclusive tasks and one exclusive task.
*
* There are circumstances in which we can try to wake a task which has already
* started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
* zero in this (rare) case, and we handle it by continuing to scan the queue.
*/
static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, int wake_flags,
void *key, wait_queue_entry_t *bookmark)
{
wait_queue_entry_t *curr, *next;
int cnt = 0;
lockdep_assert_held(&wq_head->lock);
if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
curr = list_next_entry(bookmark, entry);
list_del(&bookmark->entry);
bookmark->flags = 0;
} else {
curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
}
if (&curr->entry == &wq_head->head) {
return nr_exclusive;
}
list_for_each_entry_safe_from(curr, next, &wq_head->head, entry)
{
unsigned flags = curr->flags;
int ret;
if (flags & WQ_FLAG_BOOKMARK) {
continue;
}
ret = curr->func(curr, mode, wake_flags, key);
if (ret < 0) {
break;
}
if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) {
break;
}
if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) && (&next->entry != &wq_head->head)) {
bookmark->flags = WQ_FLAG_BOOKMARK;
list_add_tail(&bookmark->entry, &next->entry);
break;
}
}
return nr_exclusive;
}
static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, int wake_flags,
void *key)
{
unsigned long flags;
wait_queue_entry_t bookmark;
bookmark.flags = 0;
bookmark.private = NULL;
bookmark.func = NULL;
INIT_LIST_HEAD(&bookmark.entry);
do {
spin_lock_irqsave(&wq_head->lock, flags);
nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key, &bookmark);
spin_unlock_irqrestore(&wq_head->lock, flags);
} while (bookmark.flags & WQ_FLAG_BOOKMARK);
}
* __wake_up - wake up threads blocked on a waitqueue.
* @wq_head: the waitqueue
* @mode: which threads
* @nr_exclusive: how many wake-one or wake-many threads to wake up
* @key: is directly passed to the wakeup function
*
* If this function wakes up a task, it executes a full memory barrier before
* accessing the task state.
*/
void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive, void *key)
{
__wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
}
EXPORT_SYMBOL(__wake_up);
* Same as __wake_up but called with the spinlock in wait_queue_head_t held.
*/
void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
{
__wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_locked);
void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
{
__wake_up_common(wq_head, mode, 1, 0, key, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_locked_key);
void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head, unsigned int mode, void *key,
wait_queue_entry_t *bookmark)
{
__wake_up_common(wq_head, mode, 1, 0, key, bookmark);
}
EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
* __wake_up_sync_key - wake up threads blocked on a waitqueue.
* @wq_head: the waitqueue
* @mode: which threads
* @key: opaque value to be passed to wakeup targets
*
* The sync wakeup differs that the waker knows that it will schedule
* away soon, so while the target thread will be woken up, it will not
* be migrated to another CPU - ie. the two threads are 'synchronized'
* with each other. This can prevent needless bouncing between CPUs.
*
* On UP it can prevent extra preemption.
*
* If this function wakes up a task, it executes a full memory barrier before
* accessing the task state.
*/
void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
{
if (unlikely(!wq_head)) {
return;
}
__wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
}
EXPORT_SYMBOL_GPL(__wake_up_sync_key);
* __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
* @wq_head: the waitqueue
* @mode: which threads
* @key: opaque value to be passed to wakeup targets
*
* The sync wakeup differs in that the waker knows that it will schedule
* away soon, so while the target thread will be woken up, it will not
* be migrated to another CPU - ie. the two threads are 'synchronized'
* with each other. This can prevent needless bouncing between CPUs.
*
* On UP it can prevent extra preemption.
*
* If this function wakes up a task, it executes a full memory barrier before
* accessing the task state.
*/
void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
{
__wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
* __wake_up_sync - see __wake_up_sync_key()
*/
void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
{
__wake_up_sync_key(wq_head, mode, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_sync);
void __wake_up_pollfree(struct wait_queue_head *wq_head)
{
__wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
WARN_ON_ONCE(waitqueue_active(wq_head));
}
* Note: we use "set_current_state()" _after_ the wait-queue add,
* because we need a memory barrier there on SMP, so that any
* wake-function that tests for the wait-queue being active
* will be guaranteed to see waitqueue addition _or_ subsequent
* tests in this thread will see the wakeup having taken place.
*
* The spin_unlock() itself is semi-permeable and only protects
* one way (it only protects stuff inside the critical region and
* stops them from bleeding out - it would still allow subsequent
* loads to move into the critical region).
*/
void prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
{
unsigned long flags;
wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
if (list_empty(&wq_entry->entry)) {
__add_wait_queue(wq_head, wq_entry);
}
set_current_state(state);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(prepare_to_wait);
bool prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
{
unsigned long flags;
bool was_empty = false;
wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
if (list_empty(&wq_entry->entry)) {
was_empty = list_empty(&wq_head->head);
__add_wait_queue_entry_tail(wq_head, wq_entry);
}
set_current_state(state);
spin_unlock_irqrestore(&wq_head->lock, flags);
return was_empty;
}
EXPORT_SYMBOL(prepare_to_wait_exclusive);
void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
{
wq_entry->flags = flags;
wq_entry->private = current;
wq_entry->func = autoremove_wake_function;
INIT_LIST_HEAD(&wq_entry->entry);
}
EXPORT_SYMBOL(init_wait_entry);
long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
{
unsigned long flags;
long ret = 0;
spin_lock_irqsave(&wq_head->lock, flags);
if (signal_pending_state(state, current)) {
* Exclusive waiter must not fail if it was selected by wakeup,
* it should "consume" the condition we were waiting for.
*
* The caller will recheck the condition and return success if
* we were already woken up, we can not miss the event because
* wakeup locks/unlocks the same wq_head->lock.
*
* But we need to ensure that set-condition + wakeup after that
* can't see us, it should wake up another exclusive waiter if
* we fail.
*/
list_del_init(&wq_entry->entry);
ret = -ERESTARTSYS;
} else {
if (list_empty(&wq_entry->entry)) {
if (wq_entry->flags & WQ_FLAG_EXCLUSIVE) {
__add_wait_queue_entry_tail(wq_head, wq_entry);
} else {
__add_wait_queue(wq_head, wq_entry);
}
}
set_current_state(state);
}
spin_unlock_irqrestore(&wq_head->lock, flags);
return ret;
}
EXPORT_SYMBOL(prepare_to_wait_event);
* Note! These two wait functions are entered with the
* wait-queue lock held (and interrupts off in the _irq
* case), so there is no race with testing the wakeup
* condition in the caller before they add the wait
* entry to the wake queue.
*/
int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
{
if (likely(list_empty(&wait->entry))) {
__add_wait_queue_entry_tail(wq, wait);
}
set_current_state(TASK_INTERRUPTIBLE);
if (signal_pending(current)) {
return -ERESTARTSYS;
}
spin_unlock(&wq->lock);
schedule();
spin_lock(&wq->lock);
return 0;
}
EXPORT_SYMBOL(do_wait_intr);
int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
{
if (likely(list_empty(&wait->entry))) {
__add_wait_queue_entry_tail(wq, wait);
}
set_current_state(TASK_INTERRUPTIBLE);
if (signal_pending(current)) {
return -ERESTARTSYS;
}
spin_unlock_irq(&wq->lock);
schedule();
spin_lock_irq(&wq->lock);
return 0;
}
EXPORT_SYMBOL(do_wait_intr_irq);
* finish_wait - clean up after waiting in a queue
* @wq_head: waitqueue waited on
* @wq_entry: wait descriptor
*
* Sets current thread back to running state and removes
* the wait descriptor from the given waitqueue if still
* queued.
*/
void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{
unsigned long flags;
__set_current_state(TASK_RUNNING);
* We can check for list emptiness outside the lock
* IFF:
* - we use the "careful" check that verifies both
* the next and prev pointers, so that there cannot
* be any half-pending updates in progress on other
* CPU's that we haven't seen yet (and that might
* still change the stack area.
* and
* - all other users take the lock (ie we can only
* have _one_ other CPU that looks at or modifies
* the list).
*/
if (!list_empty_careful(&wq_entry->entry)) {
spin_lock_irqsave(&wq_head->lock, flags);
list_del_init(&wq_entry->entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
}
EXPORT_SYMBOL(finish_wait);
__sched int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int sync, void *key)
{
int ret = default_wake_function(wq_entry, mode, sync, key);
if (ret) {
list_del_init_careful(&wq_entry->entry);
}
return ret;
}
EXPORT_SYMBOL(autoremove_wake_function);
static inline bool is_kthread_should_stop(void)
{
return (current->flags & PF_KTHREAD) && kthread_should_stop();
}
* DEFINE_WAIT_FUNC(wait, woken_wake_func);
*
* add_wait_queue(&wq_head, &wait);
* for (;;) {
* if (condition)
* break;
*
* // in wait_woken() // in woken_wake_function()
*
* p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
* smp_mb(); // A try_to_wake_up():
* if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
* schedule() if (p->state & mode)
* p->state = TASK_RUNNING; p->state = TASK_RUNNING;
* wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
* smp_mb(); // B condition = true;
* } smp_mb(); // C
* remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
*/
__sched long wait_woken(struct wait_queue_entry *wq_entry, unsigned int mode, long timeout)
{
* The below executes an smp_mb(), which matches with the full barrier
* executed by the try_to_wake_up() in woken_wake_function() such that
* either we see the store to wq_entry->flags in woken_wake_function()
* or woken_wake_function() sees our store to current->state.
*/
set_current_state(mode);
if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) {
timeout = schedule_timeout(timeout);
}
__set_current_state(TASK_RUNNING);
* The below executes an smp_mb(), which matches with the smp_mb() (C)
* in woken_wake_function() such that either we see the wait condition
* being true or the store to wq_entry->flags in woken_wake_function()
* follows ours in the coherence order.
*/
smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN);
return timeout;
}
EXPORT_SYMBOL(wait_woken);
__sched int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int sync, void *key)
{
smp_mb();
wq_entry->flags |= WQ_FLAG_WOKEN;
return default_wake_function(wq_entry, mode, sync, key);
}
EXPORT_SYMBOL(woken_wake_function);