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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 <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
13void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
14{
15 spin_lock_init(&q->lock);
16 lockdep_set_class_and_name(&q->lock, key, name);
17 INIT_LIST_HEAD(&q->task_list);
18}
19
20EXPORT_SYMBOL(__init_waitqueue_head);
21
22void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
23{
24 unsigned long flags;
25
26 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
27 spin_lock_irqsave(&q->lock, flags);
28 __add_wait_queue(q, wait);
29 spin_unlock_irqrestore(&q->lock, flags);
30}
31EXPORT_SYMBOL(add_wait_queue);
32
33void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
34{
35 unsigned long flags;
36
37 wait->flags |= WQ_FLAG_EXCLUSIVE;
38 spin_lock_irqsave(&q->lock, flags);
39 __add_wait_queue_tail(q, wait);
40 spin_unlock_irqrestore(&q->lock, flags);
41}
42EXPORT_SYMBOL(add_wait_queue_exclusive);
43
44void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
45{
46 unsigned long flags;
47
48 spin_lock_irqsave(&q->lock, flags);
49 __remove_wait_queue(q, wait);
50 spin_unlock_irqrestore(&q->lock, flags);
51}
52EXPORT_SYMBOL(remove_wait_queue);
53
54
55/*
56 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
57 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
58 * number) then we wake all the non-exclusive tasks and one exclusive task.
59 *
60 * There are circumstances in which we can try to wake a task which has already
61 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
62 * zero in this (rare) case, and we handle it by continuing to scan the queue.
63 */
64static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
65 int nr_exclusive, int wake_flags, void *key)
66{
67 wait_queue_t *curr, *next;
68
69 list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
70 unsigned flags = curr->flags;
71
72 if (curr->func(curr, mode, wake_flags, key) &&
73 (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
74 break;
75 }
76}
77
78/**
79 * __wake_up - wake up threads blocked on a waitqueue.
80 * @q: the waitqueue
81 * @mode: which threads
82 * @nr_exclusive: how many wake-one or wake-many threads to wake up
83 * @key: is directly passed to the wakeup function
84 *
85 * It may be assumed that this function implies a write memory barrier before
86 * changing the task state if and only if any tasks are woken up.
87 */
88void __wake_up(wait_queue_head_t *q, unsigned int mode,
89 int nr_exclusive, void *key)
90{
91 unsigned long flags;
92
93 spin_lock_irqsave(&q->lock, flags);
94 __wake_up_common(q, mode, nr_exclusive, 0, key);
95 spin_unlock_irqrestore(&q->lock, flags);
96}
97EXPORT_SYMBOL(__wake_up);
98
99/*
100 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
101 */
102void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
103{
104 __wake_up_common(q, mode, nr, 0, NULL);
105}
106EXPORT_SYMBOL_GPL(__wake_up_locked);
107
108void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
109{
110 __wake_up_common(q, mode, 1, 0, key);
111}
112EXPORT_SYMBOL_GPL(__wake_up_locked_key);
113
114/**
115 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
116 * @q: the waitqueue
117 * @mode: which threads
118 * @nr_exclusive: how many wake-one or wake-many threads to wake up
119 * @key: opaque value to be passed to wakeup targets
120 *
121 * The sync wakeup differs that the waker knows that it will schedule
122 * away soon, so while the target thread will be woken up, it will not
123 * be migrated to another CPU - ie. the two threads are 'synchronized'
124 * with each other. This can prevent needless bouncing between CPUs.
125 *
126 * On UP it can prevent extra preemption.
127 *
128 * It may be assumed that this function implies a write memory barrier before
129 * changing the task state if and only if any tasks are woken up.
130 */
131void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
132 int nr_exclusive, void *key)
133{
134 unsigned long flags;
135 int wake_flags = 1; /* XXX WF_SYNC */
136
137 if (unlikely(!q))
138 return;
139
140 if (unlikely(nr_exclusive != 1))
141 wake_flags = 0;
142
143 spin_lock_irqsave(&q->lock, flags);
144 __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
145 spin_unlock_irqrestore(&q->lock, flags);
146}
147EXPORT_SYMBOL_GPL(__wake_up_sync_key);
148
149/*
150 * __wake_up_sync - see __wake_up_sync_key()
151 */
152void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
153{
154 __wake_up_sync_key(q, mode, nr_exclusive, NULL);
155}
156EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
157
158/*
159 * Note: we use "set_current_state()" _after_ the wait-queue add,
160 * because we need a memory barrier there on SMP, so that any
161 * wake-function that tests for the wait-queue being active
162 * will be guaranteed to see waitqueue addition _or_ subsequent
163 * tests in this thread will see the wakeup having taken place.
164 *
165 * The spin_unlock() itself is semi-permeable and only protects
166 * one way (it only protects stuff inside the critical region and
167 * stops them from bleeding out - it would still allow subsequent
168 * loads to move into the critical region).
169 */
170void
171prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
172{
173 unsigned long flags;
174
175 wait->flags &= ~WQ_FLAG_EXCLUSIVE;
176 spin_lock_irqsave(&q->lock, flags);
177 if (list_empty(&wait->task_list))
178 __add_wait_queue(q, wait);
179 set_current_state(state);
180 spin_unlock_irqrestore(&q->lock, flags);
181}
182EXPORT_SYMBOL(prepare_to_wait);
183
184void
185prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
186{
187 unsigned long flags;
188
189 wait->flags |= WQ_FLAG_EXCLUSIVE;
190 spin_lock_irqsave(&q->lock, flags);
191 if (list_empty(&wait->task_list))
192 __add_wait_queue_tail(q, wait);
193 set_current_state(state);
194 spin_unlock_irqrestore(&q->lock, flags);
195}
196EXPORT_SYMBOL(prepare_to_wait_exclusive);
197
198long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
199{
200 unsigned long flags;
201
202 if (signal_pending_state(state, current))
203 return -ERESTARTSYS;
204
205 wait->private = current;
206 wait->func = autoremove_wake_function;
207
208 spin_lock_irqsave(&q->lock, flags);
209 if (list_empty(&wait->task_list)) {
210 if (wait->flags & WQ_FLAG_EXCLUSIVE)
211 __add_wait_queue_tail(q, wait);
212 else
213 __add_wait_queue(q, wait);
214 }
215 set_current_state(state);
216 spin_unlock_irqrestore(&q->lock, flags);
217
218 return 0;
219}
220EXPORT_SYMBOL(prepare_to_wait_event);
221
222/**
223 * finish_wait - clean up after waiting in a queue
224 * @q: waitqueue waited on
225 * @wait: wait descriptor
226 *
227 * Sets current thread back to running state and removes
228 * the wait descriptor from the given waitqueue if still
229 * queued.
230 */
231void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
232{
233 unsigned long flags;
234
235 __set_current_state(TASK_RUNNING);
236 /*
237 * We can check for list emptiness outside the lock
238 * IFF:
239 * - we use the "careful" check that verifies both
240 * the next and prev pointers, so that there cannot
241 * be any half-pending updates in progress on other
242 * CPU's that we haven't seen yet (and that might
243 * still change the stack area.
244 * and
245 * - all other users take the lock (ie we can only
246 * have _one_ other CPU that looks at or modifies
247 * the list).
248 */
249 if (!list_empty_careful(&wait->task_list)) {
250 spin_lock_irqsave(&q->lock, flags);
251 list_del_init(&wait->task_list);
252 spin_unlock_irqrestore(&q->lock, flags);
253 }
254}
255EXPORT_SYMBOL(finish_wait);
256
257/**
258 * abort_exclusive_wait - abort exclusive waiting in a queue
259 * @q: waitqueue waited on
260 * @wait: wait descriptor
261 * @mode: runstate of the waiter to be woken
262 * @key: key to identify a wait bit queue or %NULL
263 *
264 * Sets current thread back to running state and removes
265 * the wait descriptor from the given waitqueue if still
266 * queued.
267 *
268 * Wakes up the next waiter if the caller is concurrently
269 * woken up through the queue.
270 *
271 * This prevents waiter starvation where an exclusive waiter
272 * aborts and is woken up concurrently and no one wakes up
273 * the next waiter.
274 */
275void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
276 unsigned int mode, void *key)
277{
278 unsigned long flags;
279
280 __set_current_state(TASK_RUNNING);
281 spin_lock_irqsave(&q->lock, flags);
282 if (!list_empty(&wait->task_list))
283 list_del_init(&wait->task_list);
284 else if (waitqueue_active(q))
285 __wake_up_locked_key(q, mode, key);
286 spin_unlock_irqrestore(&q->lock, flags);
287}
288EXPORT_SYMBOL(abort_exclusive_wait);
289
290int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
291{
292 int ret = default_wake_function(wait, mode, sync, key);
293
294 if (ret)
295 list_del_init(&wait->task_list);
296 return ret;
297}
298EXPORT_SYMBOL(autoremove_wake_function);
299
300int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
301{
302 struct wait_bit_key *key = arg;
303 struct wait_bit_queue *wait_bit
304 = container_of(wait, struct wait_bit_queue, wait);
305
306 if (wait_bit->key.flags != key->flags ||
307 wait_bit->key.bit_nr != key->bit_nr ||
308 test_bit(key->bit_nr, key->flags))
309 return 0;
310 else
311 return autoremove_wake_function(wait, mode, sync, key);
312}
313EXPORT_SYMBOL(wake_bit_function);
314
315/*
316 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
317 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
318 * permitted return codes. Nonzero return codes halt waiting and return.
319 */
320int __sched
321__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
322 int (*action)(void *), unsigned mode)
323{
324 int ret = 0;
325
326 do {
327 prepare_to_wait(wq, &q->wait, mode);
328 if (test_bit(q->key.bit_nr, q->key.flags))
329 ret = (*action)(q->key.flags);
330 } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
331 finish_wait(wq, &q->wait);
332 return ret;
333}
334EXPORT_SYMBOL(__wait_on_bit);
335
336int __sched out_of_line_wait_on_bit(void *word, int bit,
337 int (*action)(void *), unsigned mode)
338{
339 wait_queue_head_t *wq = bit_waitqueue(word, bit);
340 DEFINE_WAIT_BIT(wait, word, bit);
341
342 return __wait_on_bit(wq, &wait, action, mode);
343}
344EXPORT_SYMBOL(out_of_line_wait_on_bit);
345
346int __sched
347__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
348 int (*action)(void *), unsigned mode)
349{
350 do {
351 int ret;
352
353 prepare_to_wait_exclusive(wq, &q->wait, mode);
354 if (!test_bit(q->key.bit_nr, q->key.flags))
355 continue;
356 ret = action(q->key.flags);
357 if (!ret)
358 continue;
359 abort_exclusive_wait(wq, &q->wait, mode, &q->key);
360 return ret;
361 } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
362 finish_wait(wq, &q->wait);
363 return 0;
364}
365EXPORT_SYMBOL(__wait_on_bit_lock);
366
367int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
368 int (*action)(void *), unsigned mode)
369{
370 wait_queue_head_t *wq = bit_waitqueue(word, bit);
371 DEFINE_WAIT_BIT(wait, word, bit);
372
373 return __wait_on_bit_lock(wq, &wait, action, mode);
374}
375EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
376
377void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
378{
379 struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
380 if (waitqueue_active(wq))
381 __wake_up(wq, TASK_NORMAL, 1, &key);
382}
383EXPORT_SYMBOL(__wake_up_bit);
384
385/**
386 * wake_up_bit - wake up a waiter on a bit
387 * @word: the word being waited on, a kernel virtual address
388 * @bit: the bit of the word being waited on
389 *
390 * There is a standard hashed waitqueue table for generic use. This
391 * is the part of the hashtable's accessor API that wakes up waiters
392 * on a bit. For instance, if one were to have waiters on a bitflag,
393 * one would call wake_up_bit() after clearing the bit.
394 *
395 * In order for this to function properly, as it uses waitqueue_active()
396 * internally, some kind of memory barrier must be done prior to calling
397 * this. Typically, this will be smp_mb__after_clear_bit(), but in some
398 * cases where bitflags are manipulated non-atomically under a lock, one
399 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
400 * because spin_unlock() does not guarantee a memory barrier.
401 */
402void wake_up_bit(void *word, int bit)
403{
404 __wake_up_bit(bit_waitqueue(word, bit), word, bit);
405}
406EXPORT_SYMBOL(wake_up_bit);
407
408wait_queue_head_t *bit_waitqueue(void *word, int bit)
409{
410 const int shift = BITS_PER_LONG == 32 ? 5 : 6;
411 const struct zone *zone = page_zone(virt_to_page(word));
412 unsigned long val = (unsigned long)word << shift | bit;
413
414 return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
415}
416EXPORT_SYMBOL(bit_waitqueue);
417
418/*
419 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
420 * index (we're keying off bit -1, but that would produce a horrible hash
421 * value).
422 */
423static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
424{
425 if (BITS_PER_LONG == 64) {
426 unsigned long q = (unsigned long)p;
427 return bit_waitqueue((void *)(q & ~1), q & 1);
428 }
429 return bit_waitqueue(p, 0);
430}
431
432static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
433 void *arg)
434{
435 struct wait_bit_key *key = arg;
436 struct wait_bit_queue *wait_bit
437 = container_of(wait, struct wait_bit_queue, wait);
438 atomic_t *val = key->flags;
439
440 if (wait_bit->key.flags != key->flags ||
441 wait_bit->key.bit_nr != key->bit_nr ||
442 atomic_read(val) != 0)
443 return 0;
444 return autoremove_wake_function(wait, mode, sync, key);
445}
446
447/*
448 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
449 * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
450 * return codes halt waiting and return.
451 */
452static __sched
453int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
454 int (*action)(atomic_t *), unsigned mode)
455{
456 atomic_t *val;
457 int ret = 0;
458
459 do {
460 prepare_to_wait(wq, &q->wait, mode);
461 val = q->key.flags;
462 if (atomic_read(val) == 0)
463 break;
464 ret = (*action)(val);
465 } while (!ret && atomic_read(val) != 0);
466 finish_wait(wq, &q->wait);
467 return ret;
468}
469
470#define DEFINE_WAIT_ATOMIC_T(name, p) \
471 struct wait_bit_queue name = { \
472 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
473 .wait = { \
474 .private = current, \
475 .func = wake_atomic_t_function, \
476 .task_list = \
477 LIST_HEAD_INIT((name).wait.task_list), \
478 }, \
479 }
480
481__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
482 unsigned mode)
483{
484 wait_queue_head_t *wq = atomic_t_waitqueue(p);
485 DEFINE_WAIT_ATOMIC_T(wait, p);
486
487 return __wait_on_atomic_t(wq, &wait, action, mode);
488}
489EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
490
491/**
492 * wake_up_atomic_t - Wake up a waiter on a atomic_t
493 * @p: The atomic_t being waited on, a kernel virtual address
494 *
495 * Wake up anyone waiting for the atomic_t to go to zero.
496 *
497 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
498 * check is done by the waiter's wake function, not the by the waker itself).
499 */
500void wake_up_atomic_t(atomic_t *p)
501{
502 __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
503}
504EXPORT_SYMBOL(wake_up_atomic_t);