1 // SPDX-License-Identifier: GPL-2.0-only
3 * Generic waiting primitives.
5 * (C) 2004 Nadia Yvette Chambers, Oracle
9 void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
11 spin_lock_init(&wq_head->lock);
12 lockdep_set_class_and_name(&wq_head->lock, key, name);
13 INIT_LIST_HEAD(&wq_head->head);
16 EXPORT_SYMBOL(__init_waitqueue_head);
18 void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
22 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
23 spin_lock_irqsave(&wq_head->lock, flags);
24 __add_wait_queue(wq_head, wq_entry);
25 spin_unlock_irqrestore(&wq_head->lock, flags);
27 EXPORT_SYMBOL(add_wait_queue);
29 void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
33 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
34 spin_lock_irqsave(&wq_head->lock, flags);
35 __add_wait_queue_entry_tail(wq_head, wq_entry);
36 spin_unlock_irqrestore(&wq_head->lock, flags);
38 EXPORT_SYMBOL(add_wait_queue_exclusive);
40 void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
44 wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
45 spin_lock_irqsave(&wq_head->lock, flags);
46 __add_wait_queue(wq_head, wq_entry);
47 spin_unlock_irqrestore(&wq_head->lock, flags);
49 EXPORT_SYMBOL_GPL(add_wait_queue_priority);
51 void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
55 spin_lock_irqsave(&wq_head->lock, flags);
56 __remove_wait_queue(wq_head, wq_entry);
57 spin_unlock_irqrestore(&wq_head->lock, flags);
59 EXPORT_SYMBOL(remove_wait_queue);
62 * Scan threshold to break wait queue walk.
63 * This allows a waker to take a break from holding the
64 * wait queue lock during the wait queue walk.
66 #define WAITQUEUE_WALK_BREAK_CNT 64
69 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
70 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
71 * number) then we wake that number of exclusive tasks, and potentially all
72 * the non-exclusive tasks. Normally, exclusive tasks will be at the end of
73 * the list and any non-exclusive tasks will be woken first. A priority task
74 * may be at the head of the list, and can consume the event without any other
77 * There are circumstances in which we can try to wake a task which has already
78 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
79 * zero in this (rare) case, and we handle it by continuing to scan the queue.
81 static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
82 int nr_exclusive, int wake_flags, void *key,
83 wait_queue_entry_t *bookmark)
85 wait_queue_entry_t *curr, *next;
88 lockdep_assert_held(&wq_head->lock);
90 if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
91 curr = list_next_entry(bookmark, entry);
93 list_del(&bookmark->entry);
96 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
98 if (&curr->entry == &wq_head->head)
101 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
102 unsigned flags = curr->flags;
105 if (flags & WQ_FLAG_BOOKMARK)
108 ret = curr->func(curr, mode, wake_flags, key);
111 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
114 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
115 (&next->entry != &wq_head->head)) {
116 bookmark->flags = WQ_FLAG_BOOKMARK;
117 list_add_tail(&bookmark->entry, &next->entry);
125 static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
126 int nr_exclusive, int wake_flags, void *key)
129 wait_queue_entry_t bookmark;
132 bookmark.private = NULL;
133 bookmark.func = NULL;
134 INIT_LIST_HEAD(&bookmark.entry);
137 spin_lock_irqsave(&wq_head->lock, flags);
138 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
139 wake_flags, key, &bookmark);
140 spin_unlock_irqrestore(&wq_head->lock, flags);
141 } while (bookmark.flags & WQ_FLAG_BOOKMARK);
145 * __wake_up - wake up threads blocked on a waitqueue.
146 * @wq_head: the waitqueue
147 * @mode: which threads
148 * @nr_exclusive: how many wake-one or wake-many threads to wake up
149 * @key: is directly passed to the wakeup function
151 * If this function wakes up a task, it executes a full memory barrier before
152 * accessing the task state.
154 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
155 int nr_exclusive, void *key)
157 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
159 EXPORT_SYMBOL(__wake_up);
162 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
164 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
166 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
168 EXPORT_SYMBOL_GPL(__wake_up_locked);
170 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
172 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
174 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
176 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
177 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
179 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
181 EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
184 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
185 * @wq_head: the waitqueue
186 * @mode: which threads
187 * @key: opaque value to be passed to wakeup targets
189 * The sync wakeup differs that the waker knows that it will schedule
190 * away soon, so while the target thread will be woken up, it will not
191 * be migrated to another CPU - ie. the two threads are 'synchronized'
192 * with each other. This can prevent needless bouncing between CPUs.
194 * On UP it can prevent extra preemption.
196 * If this function wakes up a task, it executes a full memory barrier before
197 * accessing the task state.
199 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
202 if (unlikely(!wq_head))
205 __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
207 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
210 * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
211 * @wq_head: the waitqueue
212 * @mode: which threads
213 * @key: opaque value to be passed to wakeup targets
215 * The sync wakeup differs in that the waker knows that it will schedule
216 * away soon, so while the target thread will be woken up, it will not
217 * be migrated to another CPU - ie. the two threads are 'synchronized'
218 * with each other. This can prevent needless bouncing between CPUs.
220 * On UP it can prevent extra preemption.
222 * If this function wakes up a task, it executes a full memory barrier before
223 * accessing the task state.
225 void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
226 unsigned int mode, void *key)
228 __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
230 EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
233 * __wake_up_sync - see __wake_up_sync_key()
235 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
237 __wake_up_sync_key(wq_head, mode, NULL);
239 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
241 void __wake_up_pollfree(struct wait_queue_head *wq_head)
243 __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
244 /* POLLFREE must have cleared the queue. */
245 WARN_ON_ONCE(waitqueue_active(wq_head));
249 * Note: we use "set_current_state()" _after_ the wait-queue add,
250 * because we need a memory barrier there on SMP, so that any
251 * wake-function that tests for the wait-queue being active
252 * will be guaranteed to see waitqueue addition _or_ subsequent
253 * tests in this thread will see the wakeup having taken place.
255 * The spin_unlock() itself is semi-permeable and only protects
256 * one way (it only protects stuff inside the critical region and
257 * stops them from bleeding out - it would still allow subsequent
258 * loads to move into the critical region).
261 prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
265 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
266 spin_lock_irqsave(&wq_head->lock, flags);
267 if (list_empty(&wq_entry->entry))
268 __add_wait_queue(wq_head, wq_entry);
269 set_current_state(state);
270 spin_unlock_irqrestore(&wq_head->lock, flags);
272 EXPORT_SYMBOL(prepare_to_wait);
274 /* Returns true if we are the first waiter in the queue, false otherwise. */
276 prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
279 bool was_empty = false;
281 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
282 spin_lock_irqsave(&wq_head->lock, flags);
283 if (list_empty(&wq_entry->entry)) {
284 was_empty = list_empty(&wq_head->head);
285 __add_wait_queue_entry_tail(wq_head, wq_entry);
287 set_current_state(state);
288 spin_unlock_irqrestore(&wq_head->lock, flags);
291 EXPORT_SYMBOL(prepare_to_wait_exclusive);
293 void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
295 wq_entry->flags = flags;
296 wq_entry->private = current;
297 wq_entry->func = autoremove_wake_function;
298 INIT_LIST_HEAD(&wq_entry->entry);
300 EXPORT_SYMBOL(init_wait_entry);
302 long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
307 spin_lock_irqsave(&wq_head->lock, flags);
308 if (signal_pending_state(state, current)) {
310 * Exclusive waiter must not fail if it was selected by wakeup,
311 * it should "consume" the condition we were waiting for.
313 * The caller will recheck the condition and return success if
314 * we were already woken up, we can not miss the event because
315 * wakeup locks/unlocks the same wq_head->lock.
317 * But we need to ensure that set-condition + wakeup after that
318 * can't see us, it should wake up another exclusive waiter if
321 list_del_init(&wq_entry->entry);
324 if (list_empty(&wq_entry->entry)) {
325 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
326 __add_wait_queue_entry_tail(wq_head, wq_entry);
328 __add_wait_queue(wq_head, wq_entry);
330 set_current_state(state);
332 spin_unlock_irqrestore(&wq_head->lock, flags);
336 EXPORT_SYMBOL(prepare_to_wait_event);
339 * Note! These two wait functions are entered with the
340 * wait-queue lock held (and interrupts off in the _irq
341 * case), so there is no race with testing the wakeup
342 * condition in the caller before they add the wait
343 * entry to the wake queue.
345 int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
347 if (likely(list_empty(&wait->entry)))
348 __add_wait_queue_entry_tail(wq, wait);
350 set_current_state(TASK_INTERRUPTIBLE);
351 if (signal_pending(current))
354 spin_unlock(&wq->lock);
356 spin_lock(&wq->lock);
360 EXPORT_SYMBOL(do_wait_intr);
362 int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
364 if (likely(list_empty(&wait->entry)))
365 __add_wait_queue_entry_tail(wq, wait);
367 set_current_state(TASK_INTERRUPTIBLE);
368 if (signal_pending(current))
371 spin_unlock_irq(&wq->lock);
373 spin_lock_irq(&wq->lock);
377 EXPORT_SYMBOL(do_wait_intr_irq);
380 * finish_wait - clean up after waiting in a queue
381 * @wq_head: waitqueue waited on
382 * @wq_entry: wait descriptor
384 * Sets current thread back to running state and removes
385 * the wait descriptor from the given waitqueue if still
388 void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
392 __set_current_state(TASK_RUNNING);
394 * We can check for list emptiness outside the lock
396 * - we use the "careful" check that verifies both
397 * the next and prev pointers, so that there cannot
398 * be any half-pending updates in progress on other
399 * CPU's that we haven't seen yet (and that might
400 * still change the stack area.
402 * - all other users take the lock (ie we can only
403 * have _one_ other CPU that looks at or modifies
406 if (!list_empty_careful(&wq_entry->entry)) {
407 spin_lock_irqsave(&wq_head->lock, flags);
408 list_del_init(&wq_entry->entry);
409 spin_unlock_irqrestore(&wq_head->lock, flags);
412 EXPORT_SYMBOL(finish_wait);
414 int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
416 int ret = default_wake_function(wq_entry, mode, sync, key);
419 list_del_init_careful(&wq_entry->entry);
423 EXPORT_SYMBOL(autoremove_wake_function);
425 static inline bool is_kthread_should_stop(void)
427 return (current->flags & PF_KTHREAD) && kthread_should_stop();
431 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
433 * add_wait_queue(&wq_head, &wait);
438 * // in wait_woken() // in woken_wake_function()
440 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
441 * smp_mb(); // A try_to_wake_up():
442 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
443 * schedule() if (p->state & mode)
444 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
445 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
446 * smp_mb(); // B condition = true;
448 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
450 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
453 * The below executes an smp_mb(), which matches with the full barrier
454 * executed by the try_to_wake_up() in woken_wake_function() such that
455 * either we see the store to wq_entry->flags in woken_wake_function()
456 * or woken_wake_function() sees our store to current->state.
458 set_current_state(mode); /* A */
459 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
460 timeout = schedule_timeout(timeout);
461 __set_current_state(TASK_RUNNING);
464 * The below executes an smp_mb(), which matches with the smp_mb() (C)
465 * in woken_wake_function() such that either we see the wait condition
466 * being true or the store to wq_entry->flags in woken_wake_function()
467 * follows ours in the coherence order.
469 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
473 EXPORT_SYMBOL(wait_woken);
475 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
477 /* Pairs with the smp_store_mb() in wait_woken(). */
479 wq_entry->flags |= WQ_FLAG_WOKEN;
481 return default_wake_function(wq_entry, mode, sync, key);
483 EXPORT_SYMBOL(woken_wake_function);