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 remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
44 spin_lock_irqsave(&wq_head->lock, flags);
45 __remove_wait_queue(wq_head, wq_entry);
46 spin_unlock_irqrestore(&wq_head->lock, flags);
48 EXPORT_SYMBOL(remove_wait_queue);
51 * Scan threshold to break wait queue walk.
52 * This allows a waker to take a break from holding the
53 * wait queue lock during the wait queue walk.
55 #define WAITQUEUE_WALK_BREAK_CNT 64
58 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
59 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
60 * number) then we wake all the non-exclusive tasks and one exclusive task.
62 * There are circumstances in which we can try to wake a task which has already
63 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
64 * zero in this (rare) case, and we handle it by continuing to scan the queue.
66 static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
67 int nr_exclusive, int wake_flags, void *key,
68 wait_queue_entry_t *bookmark)
70 wait_queue_entry_t *curr, *next;
73 lockdep_assert_held(&wq_head->lock);
75 if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
76 curr = list_next_entry(bookmark, entry);
78 list_del(&bookmark->entry);
81 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
83 if (&curr->entry == &wq_head->head)
86 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
87 unsigned flags = curr->flags;
90 if (flags & WQ_FLAG_BOOKMARK)
93 ret = curr->func(curr, mode, wake_flags, key);
96 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
99 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
100 (&next->entry != &wq_head->head)) {
101 bookmark->flags = WQ_FLAG_BOOKMARK;
102 list_add_tail(&bookmark->entry, &next->entry);
110 static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
111 int nr_exclusive, int wake_flags, void *key)
114 wait_queue_entry_t bookmark;
117 bookmark.private = NULL;
118 bookmark.func = NULL;
119 INIT_LIST_HEAD(&bookmark.entry);
122 spin_lock_irqsave(&wq_head->lock, flags);
123 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
124 wake_flags, key, &bookmark);
125 spin_unlock_irqrestore(&wq_head->lock, flags);
126 } while (bookmark.flags & WQ_FLAG_BOOKMARK);
130 * __wake_up - wake up threads blocked on a waitqueue.
131 * @wq_head: the waitqueue
132 * @mode: which threads
133 * @nr_exclusive: how many wake-one or wake-many threads to wake up
134 * @key: is directly passed to the wakeup function
136 * If this function wakes up a task, it executes a full memory barrier before
137 * accessing the task state.
139 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
140 int nr_exclusive, void *key)
142 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
144 EXPORT_SYMBOL(__wake_up);
147 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
149 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
151 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
153 EXPORT_SYMBOL_GPL(__wake_up_locked);
155 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
157 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
159 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
161 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
162 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
164 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
166 EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
169 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
170 * @wq_head: the waitqueue
171 * @mode: which threads
172 * @nr_exclusive: how many wake-one or wake-many threads to wake up
173 * @key: opaque value to be passed to wakeup targets
175 * The sync wakeup differs that the waker knows that it will schedule
176 * away soon, so while the target thread will be woken up, it will not
177 * be migrated to another CPU - ie. the two threads are 'synchronized'
178 * with each other. This can prevent needless bouncing between CPUs.
180 * On UP it can prevent extra preemption.
182 * If this function wakes up a task, it executes a full memory barrier before
183 * accessing the task state.
185 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
186 int nr_exclusive, void *key)
188 int wake_flags = 1; /* XXX WF_SYNC */
190 if (unlikely(!wq_head))
193 if (unlikely(nr_exclusive != 1))
196 __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key);
198 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
201 * __wake_up_sync - see __wake_up_sync_key()
203 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
205 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
207 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
209 void __wake_up_pollfree(struct wait_queue_head *wq_head)
211 __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
212 /* POLLFREE must have cleared the queue. */
213 WARN_ON_ONCE(waitqueue_active(wq_head));
217 * Note: we use "set_current_state()" _after_ the wait-queue add,
218 * because we need a memory barrier there on SMP, so that any
219 * wake-function that tests for the wait-queue being active
220 * will be guaranteed to see waitqueue addition _or_ subsequent
221 * tests in this thread will see the wakeup having taken place.
223 * The spin_unlock() itself is semi-permeable and only protects
224 * one way (it only protects stuff inside the critical region and
225 * stops them from bleeding out - it would still allow subsequent
226 * loads to move into the critical region).
229 prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
233 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
234 spin_lock_irqsave(&wq_head->lock, flags);
235 if (list_empty(&wq_entry->entry))
236 __add_wait_queue(wq_head, wq_entry);
237 set_current_state(state);
238 spin_unlock_irqrestore(&wq_head->lock, flags);
240 EXPORT_SYMBOL(prepare_to_wait);
242 /* Returns true if we are the first waiter in the queue, false otherwise. */
244 prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
247 bool was_empty = false;
249 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
250 spin_lock_irqsave(&wq_head->lock, flags);
251 if (list_empty(&wq_entry->entry)) {
252 was_empty = list_empty(&wq_head->head);
253 __add_wait_queue_entry_tail(wq_head, wq_entry);
255 set_current_state(state);
256 spin_unlock_irqrestore(&wq_head->lock, flags);
259 EXPORT_SYMBOL(prepare_to_wait_exclusive);
261 void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
263 wq_entry->flags = flags;
264 wq_entry->private = current;
265 wq_entry->func = autoremove_wake_function;
266 INIT_LIST_HEAD(&wq_entry->entry);
268 EXPORT_SYMBOL(init_wait_entry);
270 long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
275 spin_lock_irqsave(&wq_head->lock, flags);
276 if (signal_pending_state(state, current)) {
278 * Exclusive waiter must not fail if it was selected by wakeup,
279 * it should "consume" the condition we were waiting for.
281 * The caller will recheck the condition and return success if
282 * we were already woken up, we can not miss the event because
283 * wakeup locks/unlocks the same wq_head->lock.
285 * But we need to ensure that set-condition + wakeup after that
286 * can't see us, it should wake up another exclusive waiter if
289 list_del_init(&wq_entry->entry);
292 if (list_empty(&wq_entry->entry)) {
293 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
294 __add_wait_queue_entry_tail(wq_head, wq_entry);
296 __add_wait_queue(wq_head, wq_entry);
298 set_current_state(state);
300 spin_unlock_irqrestore(&wq_head->lock, flags);
304 EXPORT_SYMBOL(prepare_to_wait_event);
307 * Note! These two wait functions are entered with the
308 * wait-queue lock held (and interrupts off in the _irq
309 * case), so there is no race with testing the wakeup
310 * condition in the caller before they add the wait
311 * entry to the wake queue.
313 int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
315 if (likely(list_empty(&wait->entry)))
316 __add_wait_queue_entry_tail(wq, wait);
318 set_current_state(TASK_INTERRUPTIBLE);
319 if (signal_pending(current))
322 spin_unlock(&wq->lock);
324 spin_lock(&wq->lock);
328 EXPORT_SYMBOL(do_wait_intr);
330 int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
332 if (likely(list_empty(&wait->entry)))
333 __add_wait_queue_entry_tail(wq, wait);
335 set_current_state(TASK_INTERRUPTIBLE);
336 if (signal_pending(current))
339 spin_unlock_irq(&wq->lock);
341 spin_lock_irq(&wq->lock);
345 EXPORT_SYMBOL(do_wait_intr_irq);
348 * finish_wait - clean up after waiting in a queue
349 * @wq_head: waitqueue waited on
350 * @wq_entry: wait descriptor
352 * Sets current thread back to running state and removes
353 * the wait descriptor from the given waitqueue if still
356 void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
360 __set_current_state(TASK_RUNNING);
362 * We can check for list emptiness outside the lock
364 * - we use the "careful" check that verifies both
365 * the next and prev pointers, so that there cannot
366 * be any half-pending updates in progress on other
367 * CPU's that we haven't seen yet (and that might
368 * still change the stack area.
370 * - all other users take the lock (ie we can only
371 * have _one_ other CPU that looks at or modifies
374 if (!list_empty_careful(&wq_entry->entry)) {
375 spin_lock_irqsave(&wq_head->lock, flags);
376 list_del_init(&wq_entry->entry);
377 spin_unlock_irqrestore(&wq_head->lock, flags);
380 EXPORT_SYMBOL(finish_wait);
382 int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
384 int ret = default_wake_function(wq_entry, mode, sync, key);
387 list_del_init_careful(&wq_entry->entry);
391 EXPORT_SYMBOL(autoremove_wake_function);
393 static inline bool is_kthread_should_stop(void)
395 return (current->flags & PF_KTHREAD) && kthread_should_stop();
399 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
401 * add_wait_queue(&wq_head, &wait);
406 * // in wait_woken() // in woken_wake_function()
408 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
409 * smp_mb(); // A try_to_wake_up():
410 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
411 * schedule() if (p->state & mode)
412 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
413 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
414 * smp_mb(); // B condition = true;
416 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
418 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
421 * The below executes an smp_mb(), which matches with the full barrier
422 * executed by the try_to_wake_up() in woken_wake_function() such that
423 * either we see the store to wq_entry->flags in woken_wake_function()
424 * or woken_wake_function() sees our store to current->state.
426 set_current_state(mode); /* A */
427 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
428 timeout = schedule_timeout(timeout);
429 __set_current_state(TASK_RUNNING);
432 * The below executes an smp_mb(), which matches with the smp_mb() (C)
433 * in woken_wake_function() such that either we see the wait condition
434 * being true or the store to wq_entry->flags in woken_wake_function()
435 * follows ours in the coherence order.
437 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
441 EXPORT_SYMBOL(wait_woken);
443 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
445 /* Pairs with the smp_store_mb() in wait_woken(). */
447 wq_entry->flags |= WQ_FLAG_WOKEN;
449 return default_wake_function(wq_entry, mode, sync, key);
451 EXPORT_SYMBOL(woken_wake_function);