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1/*
2 * Generic waiting primitives.
3 *
4 * (C) 2004 Nadia Yvette Chambers, Oracle
5 */
6#include <linux/init.h>
7#include <linux/export.h>
8#include <linux/sched.h>
9#include <linux/mm.h>
10#include <linux/wait.h>
11#include <linux/hash.h>
12#include <linux/kthread.h>
13
14void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
15{
16 spin_lock_init(&q->lock);
17 lockdep_set_class_and_name(&q->lock, key, name);
18 INIT_LIST_HEAD(&q->task_list);
19}
20
21EXPORT_SYMBOL(__init_waitqueue_head);
22
23void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
24{
25 unsigned long flags;
26
27 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
28 spin_lock_irqsave(&q->lock, flags);
29 __add_wait_queue(q, wait);
30 spin_unlock_irqrestore(&q->lock, flags);
31}
32EXPORT_SYMBOL(add_wait_queue);
33
34void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
35{
36 unsigned long flags;
37
38 wait->flags |= WQ_FLAG_EXCLUSIVE;
39 spin_lock_irqsave(&q->lock, flags);
40 __add_wait_queue_tail(q, wait);
41 spin_unlock_irqrestore(&q->lock, flags);
42}
43EXPORT_SYMBOL(add_wait_queue_exclusive);
44
45void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
46{
47 unsigned long flags;
48
49 spin_lock_irqsave(&q->lock, flags);
50 __remove_wait_queue(q, wait);
51 spin_unlock_irqrestore(&q->lock, flags);
52}
53EXPORT_SYMBOL(remove_wait_queue);
54
55
56/*
57 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
58 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
59 * number) then we wake all the non-exclusive tasks and one exclusive task.
60 *
61 * There are circumstances in which we can try to wake a task which has already
62 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
63 * zero in this (rare) case, and we handle it by continuing to scan the queue.
64 */
65static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
66 int nr_exclusive, int wake_flags, void *key)
67{
68 wait_queue_t *curr, *next;
69
70 list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
71 unsigned flags = curr->flags;
72
73 if (curr->func(curr, mode, wake_flags, key) &&
74 (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
75 break;
76 }
77}
78
79/**
80 * __wake_up - wake up threads blocked on a waitqueue.
81 * @q: the waitqueue
82 * @mode: which threads
83 * @nr_exclusive: how many wake-one or wake-many threads to wake up
84 * @key: is directly passed to the wakeup function
85 *
86 * It may be assumed that this function implies a write memory barrier before
87 * changing the task state if and only if any tasks are woken up.
88 */
89void __wake_up(wait_queue_head_t *q, unsigned int mode,
90 int nr_exclusive, void *key)
91{
92 unsigned long flags;
93
94 spin_lock_irqsave(&q->lock, flags);
95 __wake_up_common(q, mode, nr_exclusive, 0, key);
96 spin_unlock_irqrestore(&q->lock, flags);
97}
98EXPORT_SYMBOL(__wake_up);
99
100/*
101 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
102 */
103void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
104{
105 __wake_up_common(q, mode, nr, 0, NULL);
106}
107EXPORT_SYMBOL_GPL(__wake_up_locked);
108
109void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
110{
111 __wake_up_common(q, mode, 1, 0, key);
112}
113EXPORT_SYMBOL_GPL(__wake_up_locked_key);
114
115/**
116 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
117 * @q: the waitqueue
118 * @mode: which threads
119 * @nr_exclusive: how many wake-one or wake-many threads to wake up
120 * @key: opaque value to be passed to wakeup targets
121 *
122 * The sync wakeup differs that the waker knows that it will schedule
123 * away soon, so while the target thread will be woken up, it will not
124 * be migrated to another CPU - ie. the two threads are 'synchronized'
125 * with each other. This can prevent needless bouncing between CPUs.
126 *
127 * On UP it can prevent extra preemption.
128 *
129 * It may be assumed that this function implies a write memory barrier before
130 * changing the task state if and only if any tasks are woken up.
131 */
132void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
133 int nr_exclusive, void *key)
134{
135 unsigned long flags;
136 int wake_flags = 1; /* XXX WF_SYNC */
137
138 if (unlikely(!q))
139 return;
140
141 if (unlikely(nr_exclusive != 1))
142 wake_flags = 0;
143
144 spin_lock_irqsave(&q->lock, flags);
145 __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
146 spin_unlock_irqrestore(&q->lock, flags);
147}
148EXPORT_SYMBOL_GPL(__wake_up_sync_key);
149
150/*
151 * __wake_up_sync - see __wake_up_sync_key()
152 */
153void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
154{
155 __wake_up_sync_key(q, mode, nr_exclusive, NULL);
156}
157EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
158
159/*
160 * Note: we use "set_current_state()" _after_ the wait-queue add,
161 * because we need a memory barrier there on SMP, so that any
162 * wake-function that tests for the wait-queue being active
163 * will be guaranteed to see waitqueue addition _or_ subsequent
164 * tests in this thread will see the wakeup having taken place.
165 *
166 * The spin_unlock() itself is semi-permeable and only protects
167 * one way (it only protects stuff inside the critical region and
168 * stops them from bleeding out - it would still allow subsequent
169 * loads to move into the critical region).
170 */
171void
172prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
173{
174 unsigned long flags;
175
176 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
177 spin_lock_irqsave(&q->lock, flags);
178 if (list_empty(&wait->task_list))
179 __add_wait_queue(q, wait);
180 set_current_state(state);
181 spin_unlock_irqrestore(&q->lock, flags);
182}
183EXPORT_SYMBOL(prepare_to_wait);
184
185void
186prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
187{
188 unsigned long flags;
189
190 wait->flags |= WQ_FLAG_EXCLUSIVE;
191 spin_lock_irqsave(&q->lock, flags);
192 if (list_empty(&wait->task_list))
193 __add_wait_queue_tail(q, wait);
194 set_current_state(state);
195 spin_unlock_irqrestore(&q->lock, flags);
196}
197EXPORT_SYMBOL(prepare_to_wait_exclusive);
198
199void init_wait_entry(wait_queue_t *wait, int flags)
200{
201 wait->flags = flags;
202 wait->private = current;
203 wait->func = autoremove_wake_function;
204 INIT_LIST_HEAD(&wait->task_list);
205}
206EXPORT_SYMBOL(init_wait_entry);
207
208long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
209{
210 unsigned long flags;
211 long ret = 0;
212
213 spin_lock_irqsave(&q->lock, flags);
214 if (unlikely(signal_pending_state(state, current))) {
215 /*
216 * Exclusive waiter must not fail if it was selected by wakeup,
217 * it should "consume" the condition we were waiting for.
218 *
219 * The caller will recheck the condition and return success if
220 * we were already woken up, we can not miss the event because
221 * wakeup locks/unlocks the same q->lock.
222 *
223 * But we need to ensure that set-condition + wakeup after that
224 * can't see us, it should wake up another exclusive waiter if
225 * we fail.
226 */
227 list_del_init(&wait->task_list);
228 ret = -ERESTARTSYS;
229 } else {
230 if (list_empty(&wait->task_list)) {
231 if (wait->flags & WQ_FLAG_EXCLUSIVE)
232 __add_wait_queue_tail(q, wait);
233 else
234 __add_wait_queue(q, wait);
235 }
236 set_current_state(state);
237 }
238 spin_unlock_irqrestore(&q->lock, flags);
239
240 return ret;
241}
242EXPORT_SYMBOL(prepare_to_wait_event);
243
244/**
245 * finish_wait - clean up after waiting in a queue
246 * @q: waitqueue waited on
247 * @wait: wait descriptor
248 *
249 * Sets current thread back to running state and removes
250 * the wait descriptor from the given waitqueue if still
251 * queued.
252 */
253void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
254{
255 unsigned long flags;
256
257 __set_current_state(TASK_RUNNING);
258 /*
259 * We can check for list emptiness outside the lock
260 * IFF:
261 * - we use the "careful" check that verifies both
262 * the next and prev pointers, so that there cannot
263 * be any half-pending updates in progress on other
264 * CPU's that we haven't seen yet (and that might
265 * still change the stack area.
266 * and
267 * - all other users take the lock (ie we can only
268 * have _one_ other CPU that looks at or modifies
269 * the list).
270 */
271 if (!list_empty_careful(&wait->task_list)) {
272 spin_lock_irqsave(&q->lock, flags);
273 list_del_init(&wait->task_list);
274 spin_unlock_irqrestore(&q->lock, flags);
275 }
276}
277EXPORT_SYMBOL(finish_wait);
278
279int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
280{
281 int ret = default_wake_function(wait, mode, sync, key);
282
283 if (ret)
284 list_del_init(&wait->task_list);
285 return ret;
286}
287EXPORT_SYMBOL(autoremove_wake_function);
288
289static inline bool is_kthread_should_stop(void)
290{
291 return (current->flags & PF_KTHREAD) && kthread_should_stop();
292}
293
294/*
295 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
296 *
297 * add_wait_queue(&wq, &wait);
298 * for (;;) {
299 * if (condition)
300 * break;
301 *
302 * p->state = mode; condition = true;
303 * smp_mb(); // A smp_wmb(); // C
304 * if (!wait->flags & WQ_FLAG_WOKEN) wait->flags |= WQ_FLAG_WOKEN;
305 * schedule() try_to_wake_up();
306 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
307 * wait->flags &= ~WQ_FLAG_WOKEN; condition = true;
308 * smp_mb() // B smp_wmb(); // C
309 * wait->flags |= WQ_FLAG_WOKEN;
310 * }
311 * remove_wait_queue(&wq, &wait);
312 *
313 */
314long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
315{
316 set_current_state(mode); /* A */
317 /*
318 * The above implies an smp_mb(), which matches with the smp_wmb() from
319 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
320 * also observe all state before the wakeup.
321 */
322 if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
323 timeout = schedule_timeout(timeout);
324 __set_current_state(TASK_RUNNING);
325
326 /*
327 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
328 * woken_wake_function() such that we must either observe the wait
329 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
330 * an event.
331 */
332 smp_store_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
333
334 return timeout;
335}
336EXPORT_SYMBOL(wait_woken);
337
338int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
339{
340 /*
341 * Although this function is called under waitqueue lock, LOCK
342 * doesn't imply write barrier and the users expects write
343 * barrier semantics on wakeup functions. The following
344 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
345 * and is paired with smp_store_mb() in wait_woken().
346 */
347 smp_wmb(); /* C */
348 wait->flags |= WQ_FLAG_WOKEN;
349
350 return default_wake_function(wait, mode, sync, key);
351}
352EXPORT_SYMBOL(woken_wake_function);
353
354int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
355{
356 struct wait_bit_key *key = arg;
357 struct wait_bit_queue *wait_bit
358 = container_of(wait, struct wait_bit_queue, wait);
359
360 if (wait_bit->key.flags != key->flags ||
361 wait_bit->key.bit_nr != key->bit_nr ||
362 test_bit(key->bit_nr, key->flags))
363 return 0;
364 else
365 return autoremove_wake_function(wait, mode, sync, key);
366}
367EXPORT_SYMBOL(wake_bit_function);
368
369/*
370 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
371 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
372 * permitted return codes. Nonzero return codes halt waiting and return.
373 */
374int __sched
375__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
376 wait_bit_action_f *action, unsigned mode)
377{
378 int ret = 0;
379
380 do {
381 prepare_to_wait(wq, &q->wait, mode);
382 if (test_bit(q->key.bit_nr, q->key.flags))
383 ret = (*action)(&q->key, mode);
384 } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
385 finish_wait(wq, &q->wait);
386 return ret;
387}
388EXPORT_SYMBOL(__wait_on_bit);
389
390int __sched out_of_line_wait_on_bit(void *word, int bit,
391 wait_bit_action_f *action, unsigned mode)
392{
393 wait_queue_head_t *wq = bit_waitqueue(word, bit);
394 DEFINE_WAIT_BIT(wait, word, bit);
395
396 return __wait_on_bit(wq, &wait, action, mode);
397}
398EXPORT_SYMBOL(out_of_line_wait_on_bit);
399
400int __sched out_of_line_wait_on_bit_timeout(
401 void *word, int bit, wait_bit_action_f *action,
402 unsigned mode, unsigned long timeout)
403{
404 wait_queue_head_t *wq = bit_waitqueue(word, bit);
405 DEFINE_WAIT_BIT(wait, word, bit);
406
407 wait.key.timeout = jiffies + timeout;
408 return __wait_on_bit(wq, &wait, action, mode);
409}
410EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
411
412int __sched
413__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
414 wait_bit_action_f *action, unsigned mode)
415{
416 int ret = 0;
417
418 for (;;) {
419 prepare_to_wait_exclusive(wq, &q->wait, mode);
420 if (test_bit(q->key.bit_nr, q->key.flags)) {
421 ret = action(&q->key, mode);
422 /*
423 * See the comment in prepare_to_wait_event().
424 * finish_wait() does not necessarily takes wq->lock,
425 * but test_and_set_bit() implies mb() which pairs with
426 * smp_mb__after_atomic() before wake_up_page().
427 */
428 if (ret)
429 finish_wait(wq, &q->wait);
430 }
431 if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
432 if (!ret)
433 finish_wait(wq, &q->wait);
434 return 0;
435 } else if (ret) {
436 return ret;
437 }
438 }
439}
440EXPORT_SYMBOL(__wait_on_bit_lock);
441
442int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
443 wait_bit_action_f *action, unsigned mode)
444{
445 wait_queue_head_t *wq = bit_waitqueue(word, bit);
446 DEFINE_WAIT_BIT(wait, word, bit);
447
448 return __wait_on_bit_lock(wq, &wait, action, mode);
449}
450EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
451
452void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
453{
454 struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
455 if (waitqueue_active(wq))
456 __wake_up(wq, TASK_NORMAL, 1, &key);
457}
458EXPORT_SYMBOL(__wake_up_bit);
459
460/**
461 * wake_up_bit - wake up a waiter on a bit
462 * @word: the word being waited on, a kernel virtual address
463 * @bit: the bit of the word being waited on
464 *
465 * There is a standard hashed waitqueue table for generic use. This
466 * is the part of the hashtable's accessor API that wakes up waiters
467 * on a bit. For instance, if one were to have waiters on a bitflag,
468 * one would call wake_up_bit() after clearing the bit.
469 *
470 * In order for this to function properly, as it uses waitqueue_active()
471 * internally, some kind of memory barrier must be done prior to calling
472 * this. Typically, this will be smp_mb__after_atomic(), but in some
473 * cases where bitflags are manipulated non-atomically under a lock, one
474 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
475 * because spin_unlock() does not guarantee a memory barrier.
476 */
477void wake_up_bit(void *word, int bit)
478{
479 __wake_up_bit(bit_waitqueue(word, bit), word, bit);
480}
481EXPORT_SYMBOL(wake_up_bit);
482
483/*
484 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
485 * index (we're keying off bit -1, but that would produce a horrible hash
486 * value).
487 */
488static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
489{
490 if (BITS_PER_LONG == 64) {
491 unsigned long q = (unsigned long)p;
492 return bit_waitqueue((void *)(q & ~1), q & 1);
493 }
494 return bit_waitqueue(p, 0);
495}
496
497static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
498 void *arg)
499{
500 struct wait_bit_key *key = arg;
501 struct wait_bit_queue *wait_bit
502 = container_of(wait, struct wait_bit_queue, wait);
503 atomic_t *val = key->flags;
504
505 if (wait_bit->key.flags != key->flags ||
506 wait_bit->key.bit_nr != key->bit_nr ||
507 atomic_read(val) != 0)
508 return 0;
509 return autoremove_wake_function(wait, mode, sync, key);
510}
511
512/*
513 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
514 * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
515 * return codes halt waiting and return.
516 */
517static __sched
518int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
519 int (*action)(atomic_t *), unsigned mode)
520{
521 atomic_t *val;
522 int ret = 0;
523
524 do {
525 prepare_to_wait(wq, &q->wait, mode);
526 val = q->key.flags;
527 if (atomic_read(val) == 0)
528 break;
529 ret = (*action)(val);
530 } while (!ret && atomic_read(val) != 0);
531 finish_wait(wq, &q->wait);
532 return ret;
533}
534
535#define DEFINE_WAIT_ATOMIC_T(name, p) \
536 struct wait_bit_queue name = { \
537 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
538 .wait = { \
539 .private = current, \
540 .func = wake_atomic_t_function, \
541 .task_list = \
542 LIST_HEAD_INIT((name).wait.task_list), \
543 }, \
544 }
545
546__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
547 unsigned mode)
548{
549 wait_queue_head_t *wq = atomic_t_waitqueue(p);
550 DEFINE_WAIT_ATOMIC_T(wait, p);
551
552 return __wait_on_atomic_t(wq, &wait, action, mode);
553}
554EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
555
556/**
557 * wake_up_atomic_t - Wake up a waiter on a atomic_t
558 * @p: The atomic_t being waited on, a kernel virtual address
559 *
560 * Wake up anyone waiting for the atomic_t to go to zero.
561 *
562 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
563 * check is done by the waiter's wake function, not the by the waker itself).
564 */
565void wake_up_atomic_t(atomic_t *p)
566{
567 __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
568}
569EXPORT_SYMBOL(wake_up_atomic_t);
570
571__sched int bit_wait(struct wait_bit_key *word, int mode)
572{
573 schedule();
574 if (signal_pending_state(mode, current))
575 return -EINTR;
576 return 0;
577}
578EXPORT_SYMBOL(bit_wait);
579
580__sched int bit_wait_io(struct wait_bit_key *word, int mode)
581{
582 io_schedule();
583 if (signal_pending_state(mode, current))
584 return -EINTR;
585 return 0;
586}
587EXPORT_SYMBOL(bit_wait_io);
588
589__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
590{
591 unsigned long now = READ_ONCE(jiffies);
592 if (time_after_eq(now, word->timeout))
593 return -EAGAIN;
594 schedule_timeout(word->timeout - now);
595 if (signal_pending_state(mode, current))
596 return -EINTR;
597 return 0;
598}
599EXPORT_SYMBOL_GPL(bit_wait_timeout);
600
601__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
602{
603 unsigned long now = READ_ONCE(jiffies);
604 if (time_after_eq(now, word->timeout))
605 return -EAGAIN;
606 io_schedule_timeout(word->timeout - now);
607 if (signal_pending_state(mode, current))
608 return -EINTR;
609 return 0;
610}
611EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
1/*
2 * Generic waiting primitives.
3 *
4 * (C) 2004 Nadia Yvette Chambers, Oracle
5 */
6#include "sched.h"
7
8void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
9{
10 spin_lock_init(&wq_head->lock);
11 lockdep_set_class_and_name(&wq_head->lock, key, name);
12 INIT_LIST_HEAD(&wq_head->head);
13}
14
15EXPORT_SYMBOL(__init_waitqueue_head);
16
17void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
18{
19 unsigned long flags;
20
21 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
22 spin_lock_irqsave(&wq_head->lock, flags);
23 __add_wait_queue(wq_head, wq_entry);
24 spin_unlock_irqrestore(&wq_head->lock, flags);
25}
26EXPORT_SYMBOL(add_wait_queue);
27
28void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
29{
30 unsigned long flags;
31
32 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
33 spin_lock_irqsave(&wq_head->lock, flags);
34 __add_wait_queue_entry_tail(wq_head, wq_entry);
35 spin_unlock_irqrestore(&wq_head->lock, flags);
36}
37EXPORT_SYMBOL(add_wait_queue_exclusive);
38
39void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
40{
41 unsigned long flags;
42
43 spin_lock_irqsave(&wq_head->lock, flags);
44 __remove_wait_queue(wq_head, wq_entry);
45 spin_unlock_irqrestore(&wq_head->lock, flags);
46}
47EXPORT_SYMBOL(remove_wait_queue);
48
49/*
50 * Scan threshold to break wait queue walk.
51 * This allows a waker to take a break from holding the
52 * wait queue lock during the wait queue walk.
53 */
54#define WAITQUEUE_WALK_BREAK_CNT 64
55
56/*
57 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
58 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
59 * number) then we wake all the non-exclusive tasks and one exclusive task.
60 *
61 * There are circumstances in which we can try to wake a task which has already
62 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
63 * zero in this (rare) case, and we handle it by continuing to scan the queue.
64 */
65static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
66 int nr_exclusive, int wake_flags, void *key,
67 wait_queue_entry_t *bookmark)
68{
69 wait_queue_entry_t *curr, *next;
70 int cnt = 0;
71
72 if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
73 curr = list_next_entry(bookmark, entry);
74
75 list_del(&bookmark->entry);
76 bookmark->flags = 0;
77 } else
78 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
79
80 if (&curr->entry == &wq_head->head)
81 return nr_exclusive;
82
83 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
84 unsigned flags = curr->flags;
85 int ret;
86
87 if (flags & WQ_FLAG_BOOKMARK)
88 continue;
89
90 ret = curr->func(curr, mode, wake_flags, key);
91 if (ret < 0)
92 break;
93 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
94 break;
95
96 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
97 (&next->entry != &wq_head->head)) {
98 bookmark->flags = WQ_FLAG_BOOKMARK;
99 list_add_tail(&bookmark->entry, &next->entry);
100 break;
101 }
102 }
103
104 return nr_exclusive;
105}
106
107static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
108 int nr_exclusive, int wake_flags, void *key)
109{
110 unsigned long flags;
111 wait_queue_entry_t bookmark;
112
113 bookmark.flags = 0;
114 bookmark.private = NULL;
115 bookmark.func = NULL;
116 INIT_LIST_HEAD(&bookmark.entry);
117
118 spin_lock_irqsave(&wq_head->lock, flags);
119 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key, &bookmark);
120 spin_unlock_irqrestore(&wq_head->lock, flags);
121
122 while (bookmark.flags & WQ_FLAG_BOOKMARK) {
123 spin_lock_irqsave(&wq_head->lock, flags);
124 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
125 wake_flags, key, &bookmark);
126 spin_unlock_irqrestore(&wq_head->lock, flags);
127 }
128}
129
130/**
131 * __wake_up - wake up threads blocked on a waitqueue.
132 * @wq_head: the waitqueue
133 * @mode: which threads
134 * @nr_exclusive: how many wake-one or wake-many threads to wake up
135 * @key: is directly passed to the wakeup function
136 *
137 * It may be assumed that this function implies a write memory barrier before
138 * changing the task state if and only if any tasks are woken up.
139 */
140void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
141 int nr_exclusive, void *key)
142{
143 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
144}
145EXPORT_SYMBOL(__wake_up);
146
147/*
148 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
149 */
150void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
151{
152 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
153}
154EXPORT_SYMBOL_GPL(__wake_up_locked);
155
156void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
157{
158 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
159}
160EXPORT_SYMBOL_GPL(__wake_up_locked_key);
161
162void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
163 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
164{
165 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
166}
167EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
168
169/**
170 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
171 * @wq_head: the waitqueue
172 * @mode: which threads
173 * @nr_exclusive: how many wake-one or wake-many threads to wake up
174 * @key: opaque value to be passed to wakeup targets
175 *
176 * The sync wakeup differs that the waker knows that it will schedule
177 * away soon, so while the target thread will be woken up, it will not
178 * be migrated to another CPU - ie. the two threads are 'synchronized'
179 * with each other. This can prevent needless bouncing between CPUs.
180 *
181 * On UP it can prevent extra preemption.
182 *
183 * It may be assumed that this function implies a write memory barrier before
184 * changing the task state if and only if any tasks are woken up.
185 */
186void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
187 int nr_exclusive, void *key)
188{
189 int wake_flags = 1; /* XXX WF_SYNC */
190
191 if (unlikely(!wq_head))
192 return;
193
194 if (unlikely(nr_exclusive != 1))
195 wake_flags = 0;
196
197 __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key);
198}
199EXPORT_SYMBOL_GPL(__wake_up_sync_key);
200
201/*
202 * __wake_up_sync - see __wake_up_sync_key()
203 */
204void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
205{
206 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
207}
208EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
209
210/*
211 * Note: we use "set_current_state()" _after_ the wait-queue add,
212 * because we need a memory barrier there on SMP, so that any
213 * wake-function that tests for the wait-queue being active
214 * will be guaranteed to see waitqueue addition _or_ subsequent
215 * tests in this thread will see the wakeup having taken place.
216 *
217 * The spin_unlock() itself is semi-permeable and only protects
218 * one way (it only protects stuff inside the critical region and
219 * stops them from bleeding out - it would still allow subsequent
220 * loads to move into the critical region).
221 */
222void
223prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
224{
225 unsigned long flags;
226
227 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
228 spin_lock_irqsave(&wq_head->lock, flags);
229 if (list_empty(&wq_entry->entry))
230 __add_wait_queue(wq_head, wq_entry);
231 set_current_state(state);
232 spin_unlock_irqrestore(&wq_head->lock, flags);
233}
234EXPORT_SYMBOL(prepare_to_wait);
235
236void
237prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
238{
239 unsigned long flags;
240
241 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
242 spin_lock_irqsave(&wq_head->lock, flags);
243 if (list_empty(&wq_entry->entry))
244 __add_wait_queue_entry_tail(wq_head, wq_entry);
245 set_current_state(state);
246 spin_unlock_irqrestore(&wq_head->lock, flags);
247}
248EXPORT_SYMBOL(prepare_to_wait_exclusive);
249
250void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
251{
252 wq_entry->flags = flags;
253 wq_entry->private = current;
254 wq_entry->func = autoremove_wake_function;
255 INIT_LIST_HEAD(&wq_entry->entry);
256}
257EXPORT_SYMBOL(init_wait_entry);
258
259long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
260{
261 unsigned long flags;
262 long ret = 0;
263
264 spin_lock_irqsave(&wq_head->lock, flags);
265 if (unlikely(signal_pending_state(state, current))) {
266 /*
267 * Exclusive waiter must not fail if it was selected by wakeup,
268 * it should "consume" the condition we were waiting for.
269 *
270 * The caller will recheck the condition and return success if
271 * we were already woken up, we can not miss the event because
272 * wakeup locks/unlocks the same wq_head->lock.
273 *
274 * But we need to ensure that set-condition + wakeup after that
275 * can't see us, it should wake up another exclusive waiter if
276 * we fail.
277 */
278 list_del_init(&wq_entry->entry);
279 ret = -ERESTARTSYS;
280 } else {
281 if (list_empty(&wq_entry->entry)) {
282 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
283 __add_wait_queue_entry_tail(wq_head, wq_entry);
284 else
285 __add_wait_queue(wq_head, wq_entry);
286 }
287 set_current_state(state);
288 }
289 spin_unlock_irqrestore(&wq_head->lock, flags);
290
291 return ret;
292}
293EXPORT_SYMBOL(prepare_to_wait_event);
294
295/*
296 * Note! These two wait functions are entered with the
297 * wait-queue lock held (and interrupts off in the _irq
298 * case), so there is no race with testing the wakeup
299 * condition in the caller before they add the wait
300 * entry to the wake queue.
301 */
302int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
303{
304 if (likely(list_empty(&wait->entry)))
305 __add_wait_queue_entry_tail(wq, wait);
306
307 set_current_state(TASK_INTERRUPTIBLE);
308 if (signal_pending(current))
309 return -ERESTARTSYS;
310
311 spin_unlock(&wq->lock);
312 schedule();
313 spin_lock(&wq->lock);
314
315 return 0;
316}
317EXPORT_SYMBOL(do_wait_intr);
318
319int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
320{
321 if (likely(list_empty(&wait->entry)))
322 __add_wait_queue_entry_tail(wq, wait);
323
324 set_current_state(TASK_INTERRUPTIBLE);
325 if (signal_pending(current))
326 return -ERESTARTSYS;
327
328 spin_unlock_irq(&wq->lock);
329 schedule();
330 spin_lock_irq(&wq->lock);
331
332 return 0;
333}
334EXPORT_SYMBOL(do_wait_intr_irq);
335
336/**
337 * finish_wait - clean up after waiting in a queue
338 * @wq_head: waitqueue waited on
339 * @wq_entry: wait descriptor
340 *
341 * Sets current thread back to running state and removes
342 * the wait descriptor from the given waitqueue if still
343 * queued.
344 */
345void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
346{
347 unsigned long flags;
348
349 __set_current_state(TASK_RUNNING);
350 /*
351 * We can check for list emptiness outside the lock
352 * IFF:
353 * - we use the "careful" check that verifies both
354 * the next and prev pointers, so that there cannot
355 * be any half-pending updates in progress on other
356 * CPU's that we haven't seen yet (and that might
357 * still change the stack area.
358 * and
359 * - all other users take the lock (ie we can only
360 * have _one_ other CPU that looks at or modifies
361 * the list).
362 */
363 if (!list_empty_careful(&wq_entry->entry)) {
364 spin_lock_irqsave(&wq_head->lock, flags);
365 list_del_init(&wq_entry->entry);
366 spin_unlock_irqrestore(&wq_head->lock, flags);
367 }
368}
369EXPORT_SYMBOL(finish_wait);
370
371int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
372{
373 int ret = default_wake_function(wq_entry, mode, sync, key);
374
375 if (ret)
376 list_del_init(&wq_entry->entry);
377
378 return ret;
379}
380EXPORT_SYMBOL(autoremove_wake_function);
381
382static inline bool is_kthread_should_stop(void)
383{
384 return (current->flags & PF_KTHREAD) && kthread_should_stop();
385}
386
387/*
388 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
389 *
390 * add_wait_queue(&wq_head, &wait);
391 * for (;;) {
392 * if (condition)
393 * break;
394 *
395 * p->state = mode; condition = true;
396 * smp_mb(); // A smp_wmb(); // C
397 * if (!wq_entry->flags & WQ_FLAG_WOKEN) wq_entry->flags |= WQ_FLAG_WOKEN;
398 * schedule() try_to_wake_up();
399 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
400 * wq_entry->flags &= ~WQ_FLAG_WOKEN; condition = true;
401 * smp_mb() // B smp_wmb(); // C
402 * wq_entry->flags |= WQ_FLAG_WOKEN;
403 * }
404 * remove_wait_queue(&wq_head, &wait);
405 *
406 */
407long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
408{
409 set_current_state(mode); /* A */
410 /*
411 * The above implies an smp_mb(), which matches with the smp_wmb() from
412 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
413 * also observe all state before the wakeup.
414 */
415 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
416 timeout = schedule_timeout(timeout);
417 __set_current_state(TASK_RUNNING);
418
419 /*
420 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
421 * woken_wake_function() such that we must either observe the wait
422 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
423 * an event.
424 */
425 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
426
427 return timeout;
428}
429EXPORT_SYMBOL(wait_woken);
430
431int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
432{
433 /*
434 * Although this function is called under waitqueue lock, LOCK
435 * doesn't imply write barrier and the users expects write
436 * barrier semantics on wakeup functions. The following
437 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
438 * and is paired with smp_store_mb() in wait_woken().
439 */
440 smp_wmb(); /* C */
441 wq_entry->flags |= WQ_FLAG_WOKEN;
442
443 return default_wake_function(wq_entry, mode, sync, key);
444}
445EXPORT_SYMBOL(woken_wake_function);