2 * Generic waiting primitives.
4 * (C) 2004 Nadia Yvette Chambers, Oracle
6 #include <linux/init.h>
7 #include <linux/export.h>
8 #include <linux/sched/signal.h>
9 #include <linux/sched/debug.h>
11 #include <linux/wait.h>
12 #include <linux/hash.h>
13 #include <linux/kthread.h>
15 void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
17 spin_lock_init(&q->lock);
18 lockdep_set_class_and_name(&q->lock, key, name);
19 INIT_LIST_HEAD(&q->task_list);
22 EXPORT_SYMBOL(__init_waitqueue_head);
24 void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
28 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
29 spin_lock_irqsave(&q->lock, flags);
30 __add_wait_queue(q, wait);
31 spin_unlock_irqrestore(&q->lock, flags);
33 EXPORT_SYMBOL(add_wait_queue);
35 void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
39 wait->flags |= WQ_FLAG_EXCLUSIVE;
40 spin_lock_irqsave(&q->lock, flags);
41 __add_wait_queue_tail(q, wait);
42 spin_unlock_irqrestore(&q->lock, flags);
44 EXPORT_SYMBOL(add_wait_queue_exclusive);
46 void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
50 spin_lock_irqsave(&q->lock, flags);
51 __remove_wait_queue(q, wait);
52 spin_unlock_irqrestore(&q->lock, flags);
54 EXPORT_SYMBOL(remove_wait_queue);
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 void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
67 int nr_exclusive, int wake_flags, void *key)
69 wait_queue_t *curr, *next;
71 list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
72 unsigned flags = curr->flags;
74 if (curr->func(curr, mode, wake_flags, key) &&
75 (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
81 * __wake_up - wake up threads blocked on a waitqueue.
83 * @mode: which threads
84 * @nr_exclusive: how many wake-one or wake-many threads to wake up
85 * @key: is directly passed to the wakeup function
87 * It may be assumed that this function implies a write memory barrier before
88 * changing the task state if and only if any tasks are woken up.
90 void __wake_up(wait_queue_head_t *q, unsigned int mode,
91 int nr_exclusive, void *key)
95 spin_lock_irqsave(&q->lock, flags);
96 __wake_up_common(q, mode, nr_exclusive, 0, key);
97 spin_unlock_irqrestore(&q->lock, flags);
99 EXPORT_SYMBOL(__wake_up);
102 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
104 void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
106 __wake_up_common(q, mode, nr, 0, NULL);
108 EXPORT_SYMBOL_GPL(__wake_up_locked);
110 void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
112 __wake_up_common(q, mode, 1, 0, key);
114 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
117 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
119 * @mode: which threads
120 * @nr_exclusive: how many wake-one or wake-many threads to wake up
121 * @key: opaque value to be passed to wakeup targets
123 * The sync wakeup differs that the waker knows that it will schedule
124 * away soon, so while the target thread will be woken up, it will not
125 * be migrated to another CPU - ie. the two threads are 'synchronized'
126 * with each other. This can prevent needless bouncing between CPUs.
128 * On UP it can prevent extra preemption.
130 * It may be assumed that this function implies a write memory barrier before
131 * changing the task state if and only if any tasks are woken up.
133 void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
134 int nr_exclusive, void *key)
137 int wake_flags = 1; /* XXX WF_SYNC */
142 if (unlikely(nr_exclusive != 1))
145 spin_lock_irqsave(&q->lock, flags);
146 __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
147 spin_unlock_irqrestore(&q->lock, flags);
149 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
152 * __wake_up_sync - see __wake_up_sync_key()
154 void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
156 __wake_up_sync_key(q, mode, nr_exclusive, NULL);
158 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
161 * Note: we use "set_current_state()" _after_ the wait-queue add,
162 * because we need a memory barrier there on SMP, so that any
163 * wake-function that tests for the wait-queue being active
164 * will be guaranteed to see waitqueue addition _or_ subsequent
165 * tests in this thread will see the wakeup having taken place.
167 * The spin_unlock() itself is semi-permeable and only protects
168 * one way (it only protects stuff inside the critical region and
169 * stops them from bleeding out - it would still allow subsequent
170 * loads to move into the critical region).
173 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
177 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
178 spin_lock_irqsave(&q->lock, flags);
179 if (list_empty(&wait->task_list))
180 __add_wait_queue(q, wait);
181 set_current_state(state);
182 spin_unlock_irqrestore(&q->lock, flags);
184 EXPORT_SYMBOL(prepare_to_wait);
187 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
191 wait->flags |= WQ_FLAG_EXCLUSIVE;
192 spin_lock_irqsave(&q->lock, flags);
193 if (list_empty(&wait->task_list))
194 __add_wait_queue_tail(q, wait);
195 set_current_state(state);
196 spin_unlock_irqrestore(&q->lock, flags);
198 EXPORT_SYMBOL(prepare_to_wait_exclusive);
200 void init_wait_entry(wait_queue_t *wait, int flags)
203 wait->private = current;
204 wait->func = autoremove_wake_function;
205 INIT_LIST_HEAD(&wait->task_list);
207 EXPORT_SYMBOL(init_wait_entry);
209 long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
214 spin_lock_irqsave(&q->lock, flags);
215 if (unlikely(signal_pending_state(state, current))) {
217 * Exclusive waiter must not fail if it was selected by wakeup,
218 * it should "consume" the condition we were waiting for.
220 * The caller will recheck the condition and return success if
221 * we were already woken up, we can not miss the event because
222 * wakeup locks/unlocks the same q->lock.
224 * But we need to ensure that set-condition + wakeup after that
225 * can't see us, it should wake up another exclusive waiter if
228 list_del_init(&wait->task_list);
231 if (list_empty(&wait->task_list)) {
232 if (wait->flags & WQ_FLAG_EXCLUSIVE)
233 __add_wait_queue_tail(q, wait);
235 __add_wait_queue(q, wait);
237 set_current_state(state);
239 spin_unlock_irqrestore(&q->lock, flags);
243 EXPORT_SYMBOL(prepare_to_wait_event);
246 * finish_wait - clean up after waiting in a queue
247 * @q: waitqueue waited on
248 * @wait: wait descriptor
250 * Sets current thread back to running state and removes
251 * the wait descriptor from the given waitqueue if still
254 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
258 __set_current_state(TASK_RUNNING);
260 * We can check for list emptiness outside the lock
262 * - we use the "careful" check that verifies both
263 * the next and prev pointers, so that there cannot
264 * be any half-pending updates in progress on other
265 * CPU's that we haven't seen yet (and that might
266 * still change the stack area.
268 * - all other users take the lock (ie we can only
269 * have _one_ other CPU that looks at or modifies
272 if (!list_empty_careful(&wait->task_list)) {
273 spin_lock_irqsave(&q->lock, flags);
274 list_del_init(&wait->task_list);
275 spin_unlock_irqrestore(&q->lock, flags);
278 EXPORT_SYMBOL(finish_wait);
280 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
282 int ret = default_wake_function(wait, mode, sync, key);
285 list_del_init(&wait->task_list);
288 EXPORT_SYMBOL(autoremove_wake_function);
290 static inline bool is_kthread_should_stop(void)
292 return (current->flags & PF_KTHREAD) && kthread_should_stop();
296 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
298 * add_wait_queue(&wq, &wait);
303 * p->state = mode; condition = true;
304 * smp_mb(); // A smp_wmb(); // C
305 * if (!wait->flags & WQ_FLAG_WOKEN) wait->flags |= WQ_FLAG_WOKEN;
306 * schedule() try_to_wake_up();
307 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
308 * wait->flags &= ~WQ_FLAG_WOKEN; condition = true;
309 * smp_mb() // B smp_wmb(); // C
310 * wait->flags |= WQ_FLAG_WOKEN;
312 * remove_wait_queue(&wq, &wait);
315 long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
317 set_current_state(mode); /* A */
319 * The above implies an smp_mb(), which matches with the smp_wmb() from
320 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
321 * also observe all state before the wakeup.
323 if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
324 timeout = schedule_timeout(timeout);
325 __set_current_state(TASK_RUNNING);
328 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
329 * woken_wake_function() such that we must either observe the wait
330 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
333 smp_store_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
337 EXPORT_SYMBOL(wait_woken);
339 int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
342 * Although this function is called under waitqueue lock, LOCK
343 * doesn't imply write barrier and the users expects write
344 * barrier semantics on wakeup functions. The following
345 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
346 * and is paired with smp_store_mb() in wait_woken().
349 wait->flags |= WQ_FLAG_WOKEN;
351 return default_wake_function(wait, mode, sync, key);
353 EXPORT_SYMBOL(woken_wake_function);
355 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
357 struct wait_bit_key *key = arg;
358 struct wait_bit_queue *wait_bit
359 = container_of(wait, struct wait_bit_queue, wait);
361 if (wait_bit->key.flags != key->flags ||
362 wait_bit->key.bit_nr != key->bit_nr ||
363 test_bit(key->bit_nr, key->flags))
366 return autoremove_wake_function(wait, mode, sync, key);
368 EXPORT_SYMBOL(wake_bit_function);
371 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
372 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
373 * permitted return codes. Nonzero return codes halt waiting and return.
376 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
377 wait_bit_action_f *action, unsigned mode)
382 prepare_to_wait(wq, &q->wait, mode);
383 if (test_bit(q->key.bit_nr, q->key.flags))
384 ret = (*action)(&q->key, mode);
385 } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
386 finish_wait(wq, &q->wait);
389 EXPORT_SYMBOL(__wait_on_bit);
391 int __sched out_of_line_wait_on_bit(void *word, int bit,
392 wait_bit_action_f *action, unsigned mode)
394 wait_queue_head_t *wq = bit_waitqueue(word, bit);
395 DEFINE_WAIT_BIT(wait, word, bit);
397 return __wait_on_bit(wq, &wait, action, mode);
399 EXPORT_SYMBOL(out_of_line_wait_on_bit);
401 int __sched out_of_line_wait_on_bit_timeout(
402 void *word, int bit, wait_bit_action_f *action,
403 unsigned mode, unsigned long timeout)
405 wait_queue_head_t *wq = bit_waitqueue(word, bit);
406 DEFINE_WAIT_BIT(wait, word, bit);
408 wait.key.timeout = jiffies + timeout;
409 return __wait_on_bit(wq, &wait, action, mode);
411 EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
414 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
415 wait_bit_action_f *action, unsigned mode)
420 prepare_to_wait_exclusive(wq, &q->wait, mode);
421 if (test_bit(q->key.bit_nr, q->key.flags)) {
422 ret = action(&q->key, mode);
424 * See the comment in prepare_to_wait_event().
425 * finish_wait() does not necessarily takes wq->lock,
426 * but test_and_set_bit() implies mb() which pairs with
427 * smp_mb__after_atomic() before wake_up_page().
430 finish_wait(wq, &q->wait);
432 if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
434 finish_wait(wq, &q->wait);
441 EXPORT_SYMBOL(__wait_on_bit_lock);
443 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
444 wait_bit_action_f *action, unsigned mode)
446 wait_queue_head_t *wq = bit_waitqueue(word, bit);
447 DEFINE_WAIT_BIT(wait, word, bit);
449 return __wait_on_bit_lock(wq, &wait, action, mode);
451 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
453 void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
455 struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
456 if (waitqueue_active(wq))
457 __wake_up(wq, TASK_NORMAL, 1, &key);
459 EXPORT_SYMBOL(__wake_up_bit);
462 * wake_up_bit - wake up a waiter on a bit
463 * @word: the word being waited on, a kernel virtual address
464 * @bit: the bit of the word being waited on
466 * There is a standard hashed waitqueue table for generic use. This
467 * is the part of the hashtable's accessor API that wakes up waiters
468 * on a bit. For instance, if one were to have waiters on a bitflag,
469 * one would call wake_up_bit() after clearing the bit.
471 * In order for this to function properly, as it uses waitqueue_active()
472 * internally, some kind of memory barrier must be done prior to calling
473 * this. Typically, this will be smp_mb__after_atomic(), but in some
474 * cases where bitflags are manipulated non-atomically under a lock, one
475 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
476 * because spin_unlock() does not guarantee a memory barrier.
478 void wake_up_bit(void *word, int bit)
480 __wake_up_bit(bit_waitqueue(word, bit), word, bit);
482 EXPORT_SYMBOL(wake_up_bit);
485 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
486 * index (we're keying off bit -1, but that would produce a horrible hash
489 static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
491 if (BITS_PER_LONG == 64) {
492 unsigned long q = (unsigned long)p;
493 return bit_waitqueue((void *)(q & ~1), q & 1);
495 return bit_waitqueue(p, 0);
498 static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
501 struct wait_bit_key *key = arg;
502 struct wait_bit_queue *wait_bit
503 = container_of(wait, struct wait_bit_queue, wait);
504 atomic_t *val = key->flags;
506 if (wait_bit->key.flags != key->flags ||
507 wait_bit->key.bit_nr != key->bit_nr ||
508 atomic_read(val) != 0)
510 return autoremove_wake_function(wait, mode, sync, key);
514 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
515 * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
516 * return codes halt waiting and return.
519 int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
520 int (*action)(atomic_t *), unsigned mode)
526 prepare_to_wait(wq, &q->wait, mode);
528 if (atomic_read(val) == 0)
530 ret = (*action)(val);
531 } while (!ret && atomic_read(val) != 0);
532 finish_wait(wq, &q->wait);
536 #define DEFINE_WAIT_ATOMIC_T(name, p) \
537 struct wait_bit_queue name = { \
538 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
540 .private = current, \
541 .func = wake_atomic_t_function, \
543 LIST_HEAD_INIT((name).wait.task_list), \
547 __sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
550 wait_queue_head_t *wq = atomic_t_waitqueue(p);
551 DEFINE_WAIT_ATOMIC_T(wait, p);
553 return __wait_on_atomic_t(wq, &wait, action, mode);
555 EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
558 * wake_up_atomic_t - Wake up a waiter on a atomic_t
559 * @p: The atomic_t being waited on, a kernel virtual address
561 * Wake up anyone waiting for the atomic_t to go to zero.
563 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
564 * check is done by the waiter's wake function, not the by the waker itself).
566 void wake_up_atomic_t(atomic_t *p)
568 __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
570 EXPORT_SYMBOL(wake_up_atomic_t);
572 __sched int bit_wait(struct wait_bit_key *word, int mode)
575 if (signal_pending_state(mode, current))
579 EXPORT_SYMBOL(bit_wait);
581 __sched int bit_wait_io(struct wait_bit_key *word, int mode)
584 if (signal_pending_state(mode, current))
588 EXPORT_SYMBOL(bit_wait_io);
590 __sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
592 unsigned long now = READ_ONCE(jiffies);
593 if (time_after_eq(now, word->timeout))
595 schedule_timeout(word->timeout - now);
596 if (signal_pending_state(mode, current))
600 EXPORT_SYMBOL_GPL(bit_wait_timeout);
602 __sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
604 unsigned long now = READ_ONCE(jiffies);
605 if (time_after_eq(now, word->timeout))
607 io_schedule_timeout(word->timeout - now);
608 if (signal_pending_state(mode, current))
612 EXPORT_SYMBOL_GPL(bit_wait_io_timeout);