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);
121 spin_lock_irqsave(&wq_head->lock, flags);
122 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key, &bookmark);
123 spin_unlock_irqrestore(&wq_head->lock, flags);
125 while (bookmark.flags & WQ_FLAG_BOOKMARK) {
126 spin_lock_irqsave(&wq_head->lock, flags);
127 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
128 wake_flags, key, &bookmark);
129 spin_unlock_irqrestore(&wq_head->lock, flags);
134 * __wake_up - wake up threads blocked on a waitqueue.
135 * @wq_head: the waitqueue
136 * @mode: which threads
137 * @nr_exclusive: how many wake-one or wake-many threads to wake up
138 * @key: is directly passed to the wakeup function
140 * If this function wakes up a task, it executes a full memory barrier before
141 * accessing the task state.
143 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
144 int nr_exclusive, void *key)
146 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
148 EXPORT_SYMBOL(__wake_up);
151 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
153 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
155 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
157 EXPORT_SYMBOL_GPL(__wake_up_locked);
159 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
161 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
163 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
165 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
166 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
168 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
170 EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
173 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
174 * @wq_head: the waitqueue
175 * @mode: which threads
176 * @nr_exclusive: how many wake-one or wake-many threads to wake up
177 * @key: opaque value to be passed to wakeup targets
179 * The sync wakeup differs that the waker knows that it will schedule
180 * away soon, so while the target thread will be woken up, it will not
181 * be migrated to another CPU - ie. the two threads are 'synchronized'
182 * with each other. This can prevent needless bouncing between CPUs.
184 * On UP it can prevent extra preemption.
186 * If this function wakes up a task, it executes a full memory barrier before
187 * accessing the task state.
189 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
190 int nr_exclusive, void *key)
192 int wake_flags = 1; /* XXX WF_SYNC */
194 if (unlikely(!wq_head))
197 if (unlikely(nr_exclusive != 1))
200 __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key);
202 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
205 * __wake_up_sync - see __wake_up_sync_key()
207 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
209 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
211 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
214 * Note: we use "set_current_state()" _after_ the wait-queue add,
215 * because we need a memory barrier there on SMP, so that any
216 * wake-function that tests for the wait-queue being active
217 * will be guaranteed to see waitqueue addition _or_ subsequent
218 * tests in this thread will see the wakeup having taken place.
220 * The spin_unlock() itself is semi-permeable and only protects
221 * one way (it only protects stuff inside the critical region and
222 * stops them from bleeding out - it would still allow subsequent
223 * loads to move into the critical region).
226 prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
230 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
231 spin_lock_irqsave(&wq_head->lock, flags);
232 if (list_empty(&wq_entry->entry))
233 __add_wait_queue(wq_head, wq_entry);
234 set_current_state(state);
235 spin_unlock_irqrestore(&wq_head->lock, flags);
237 EXPORT_SYMBOL(prepare_to_wait);
240 prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
244 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
245 spin_lock_irqsave(&wq_head->lock, flags);
246 if (list_empty(&wq_entry->entry))
247 __add_wait_queue_entry_tail(wq_head, wq_entry);
248 set_current_state(state);
249 spin_unlock_irqrestore(&wq_head->lock, flags);
251 EXPORT_SYMBOL(prepare_to_wait_exclusive);
253 void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
255 wq_entry->flags = flags;
256 wq_entry->private = current;
257 wq_entry->func = autoremove_wake_function;
258 INIT_LIST_HEAD(&wq_entry->entry);
260 EXPORT_SYMBOL(init_wait_entry);
262 long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
267 spin_lock_irqsave(&wq_head->lock, flags);
268 if (signal_pending_state(state, current)) {
270 * Exclusive waiter must not fail if it was selected by wakeup,
271 * it should "consume" the condition we were waiting for.
273 * The caller will recheck the condition and return success if
274 * we were already woken up, we can not miss the event because
275 * wakeup locks/unlocks the same wq_head->lock.
277 * But we need to ensure that set-condition + wakeup after that
278 * can't see us, it should wake up another exclusive waiter if
281 list_del_init(&wq_entry->entry);
284 if (list_empty(&wq_entry->entry)) {
285 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
286 __add_wait_queue_entry_tail(wq_head, wq_entry);
288 __add_wait_queue(wq_head, wq_entry);
290 set_current_state(state);
292 spin_unlock_irqrestore(&wq_head->lock, flags);
296 EXPORT_SYMBOL(prepare_to_wait_event);
299 * Note! These two wait functions are entered with the
300 * wait-queue lock held (and interrupts off in the _irq
301 * case), so there is no race with testing the wakeup
302 * condition in the caller before they add the wait
303 * entry to the wake queue.
305 int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
307 if (likely(list_empty(&wait->entry)))
308 __add_wait_queue_entry_tail(wq, wait);
310 set_current_state(TASK_INTERRUPTIBLE);
311 if (signal_pending(current))
314 spin_unlock(&wq->lock);
316 spin_lock(&wq->lock);
320 EXPORT_SYMBOL(do_wait_intr);
322 int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
324 if (likely(list_empty(&wait->entry)))
325 __add_wait_queue_entry_tail(wq, wait);
327 set_current_state(TASK_INTERRUPTIBLE);
328 if (signal_pending(current))
331 spin_unlock_irq(&wq->lock);
333 spin_lock_irq(&wq->lock);
337 EXPORT_SYMBOL(do_wait_intr_irq);
340 * finish_wait - clean up after waiting in a queue
341 * @wq_head: waitqueue waited on
342 * @wq_entry: wait descriptor
344 * Sets current thread back to running state and removes
345 * the wait descriptor from the given waitqueue if still
348 void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
352 __set_current_state(TASK_RUNNING);
354 * We can check for list emptiness outside the lock
356 * - we use the "careful" check that verifies both
357 * the next and prev pointers, so that there cannot
358 * be any half-pending updates in progress on other
359 * CPU's that we haven't seen yet (and that might
360 * still change the stack area.
362 * - all other users take the lock (ie we can only
363 * have _one_ other CPU that looks at or modifies
366 if (!list_empty_careful(&wq_entry->entry)) {
367 spin_lock_irqsave(&wq_head->lock, flags);
368 list_del_init(&wq_entry->entry);
369 spin_unlock_irqrestore(&wq_head->lock, flags);
372 EXPORT_SYMBOL(finish_wait);
374 int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
376 int ret = default_wake_function(wq_entry, mode, sync, key);
379 list_del_init(&wq_entry->entry);
383 EXPORT_SYMBOL(autoremove_wake_function);
385 static inline bool is_kthread_should_stop(void)
387 return (current->flags & PF_KTHREAD) && kthread_should_stop();
391 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
393 * add_wait_queue(&wq_head, &wait);
398 * // in wait_woken() // in woken_wake_function()
400 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
401 * smp_mb(); // A try_to_wake_up():
402 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
403 * schedule() if (p->state & mode)
404 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
405 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
406 * smp_mb(); // B condition = true;
408 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
410 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
413 * The below executes an smp_mb(), which matches with the full barrier
414 * executed by the try_to_wake_up() in woken_wake_function() such that
415 * either we see the store to wq_entry->flags in woken_wake_function()
416 * or woken_wake_function() sees our store to current->state.
418 set_current_state(mode); /* A */
419 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
420 timeout = schedule_timeout(timeout);
421 __set_current_state(TASK_RUNNING);
424 * The below executes an smp_mb(), which matches with the smp_mb() (C)
425 * in woken_wake_function() such that either we see the wait condition
426 * being true or the store to wq_entry->flags in woken_wake_function()
427 * follows ours in the coherence order.
429 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
433 EXPORT_SYMBOL(wait_woken);
435 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
437 /* Pairs with the smp_store_mb() in wait_woken(). */
439 wq_entry->flags |= WQ_FLAG_WOKEN;
441 return default_wake_function(wq_entry, mode, sync, key);
443 EXPORT_SYMBOL(woken_wake_function);