projects/linux·blob v4.8 · refs

624 lines · 17.7 KiB

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
199long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
200{
201 unsigned long flags;
202
203 if (signal_pending_state(state, current))
204 return -ERESTARTSYS;
205
206 wait->private = current;
207 wait->func = autoremove_wake_function;
208
209 spin_lock_irqsave(&q->lock, flags);
210 if (list_empty(&wait->task_list)) {
211 if (wait->flags & WQ_FLAG_EXCLUSIVE)
212 __add_wait_queue_tail(q, wait);
213 else
214 __add_wait_queue(q, wait);
215 }
216 set_current_state(state);
217 spin_unlock_irqrestore(&q->lock, flags);
218
219 return 0;
220}
221EXPORT_SYMBOL(prepare_to_wait_event);
222
223/**
224 * finish_wait - clean up after waiting in a queue
225 * @q: waitqueue waited on
226 * @wait: wait descriptor
227 *
228 * Sets current thread back to running state and removes
229 * the wait descriptor from the given waitqueue if still
230 * queued.
231 */
232void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
233{
234 unsigned long flags;
235
236 __set_current_state(TASK_RUNNING);
237 /*
238 * We can check for list emptiness outside the lock
239 * IFF:
240 * - we use the "careful" check that verifies both
241 * the next and prev pointers, so that there cannot
242 * be any half-pending updates in progress on other
243 * CPU's that we haven't seen yet (and that might
244 * still change the stack area.
245 * and
246 * - all other users take the lock (ie we can only
247 * have _one_ other CPU that looks at or modifies
248 * the list).
249 */
250 if (!list_empty_careful(&wait->task_list)) {
251 spin_lock_irqsave(&q->lock, flags);
252 list_del_init(&wait->task_list);
253 spin_unlock_irqrestore(&q->lock, flags);
254 }
255}
256EXPORT_SYMBOL(finish_wait);
257
258/**
259 * abort_exclusive_wait - abort exclusive waiting in a queue
260 * @q: waitqueue waited on
261 * @wait: wait descriptor
262 * @mode: runstate of the waiter to be woken
263 * @key: key to identify a wait bit queue or %NULL
264 *
265 * Sets current thread back to running state and removes
266 * the wait descriptor from the given waitqueue if still
267 * queued.
268 *
269 * Wakes up the next waiter if the caller is concurrently
270 * woken up through the queue.
271 *
272 * This prevents waiter starvation where an exclusive waiter
273 * aborts and is woken up concurrently and no one wakes up
274 * the next waiter.
275 */
276void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
277 unsigned int mode, void *key)
278{
279 unsigned long flags;
280
281 __set_current_state(TASK_RUNNING);
282 spin_lock_irqsave(&q->lock, flags);
283 if (!list_empty(&wait->task_list))
284 list_del_init(&wait->task_list);
285 else if (waitqueue_active(q))
286 __wake_up_locked_key(q, mode, key);
287 spin_unlock_irqrestore(&q->lock, flags);
288}
289EXPORT_SYMBOL(abort_exclusive_wait);
290
291int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
292{
293 int ret = default_wake_function(wait, mode, sync, key);
294
295 if (ret)
296 list_del_init(&wait->task_list);
297 return ret;
298}
299EXPORT_SYMBOL(autoremove_wake_function);
300
301static inline bool is_kthread_should_stop(void)
302{
303 return (current->flags & PF_KTHREAD) && kthread_should_stop();
304}
305
306/*
307 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
308 *
309 * add_wait_queue(&wq, &wait);
310 * for (;;) {
311 * if (condition)
312 * break;
313 *
314 * p->state = mode; condition = true;
315 * smp_mb(); // A smp_wmb(); // C
316 * if (!wait->flags & WQ_FLAG_WOKEN) wait->flags |= WQ_FLAG_WOKEN;
317 * schedule() try_to_wake_up();
318 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
319 * wait->flags &= ~WQ_FLAG_WOKEN; condition = true;
320 * smp_mb() // B smp_wmb(); // C
321 * wait->flags |= WQ_FLAG_WOKEN;
322 * }
323 * remove_wait_queue(&wq, &wait);
324 *
325 */
326long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
327{
328 set_current_state(mode); /* A */
329 /*
330 * The above implies an smp_mb(), which matches with the smp_wmb() from
331 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
332 * also observe all state before the wakeup.
333 */
334 if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
335 timeout = schedule_timeout(timeout);
336 __set_current_state(TASK_RUNNING);
337
338 /*
339 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
340 * woken_wake_function() such that we must either observe the wait
341 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
342 * an event.
343 */
344 smp_store_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
345
346 return timeout;
347}
348EXPORT_SYMBOL(wait_woken);
349
350int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
351{
352 /*
353 * Although this function is called under waitqueue lock, LOCK
354 * doesn't imply write barrier and the users expects write
355 * barrier semantics on wakeup functions. The following
356 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
357 * and is paired with smp_store_mb() in wait_woken().
358 */
359 smp_wmb(); /* C */
360 wait->flags |= WQ_FLAG_WOKEN;
361
362 return default_wake_function(wait, mode, sync, key);
363}
364EXPORT_SYMBOL(woken_wake_function);
365
366int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
367{
368 struct wait_bit_key *key = arg;
369 struct wait_bit_queue *wait_bit
370 = container_of(wait, struct wait_bit_queue, wait);
371
372 if (wait_bit->key.flags != key->flags ||
373 wait_bit->key.bit_nr != key->bit_nr ||
374 test_bit(key->bit_nr, key->flags))
375 return 0;
376 else
377 return autoremove_wake_function(wait, mode, sync, key);
378}
379EXPORT_SYMBOL(wake_bit_function);
380
381/*
382 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
383 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
384 * permitted return codes. Nonzero return codes halt waiting and return.
385 */
386int __sched
387__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
388 wait_bit_action_f *action, unsigned mode)
389{
390 int ret = 0;
391
392 do {
393 prepare_to_wait(wq, &q->wait, mode);
394 if (test_bit(q->key.bit_nr, q->key.flags))
395 ret = (*action)(&q->key, mode);
396 } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
397 finish_wait(wq, &q->wait);
398 return ret;
399}
400EXPORT_SYMBOL(__wait_on_bit);
401
402int __sched out_of_line_wait_on_bit(void *word, int bit,
403 wait_bit_action_f *action, unsigned mode)
404{
405 wait_queue_head_t *wq = bit_waitqueue(word, bit);
406 DEFINE_WAIT_BIT(wait, word, bit);
407
408 return __wait_on_bit(wq, &wait, action, mode);
409}
410EXPORT_SYMBOL(out_of_line_wait_on_bit);
411
412int __sched out_of_line_wait_on_bit_timeout(
413 void *word, int bit, wait_bit_action_f *action,
414 unsigned mode, unsigned long timeout)
415{
416 wait_queue_head_t *wq = bit_waitqueue(word, bit);
417 DEFINE_WAIT_BIT(wait, word, bit);
418
419 wait.key.timeout = jiffies + timeout;
420 return __wait_on_bit(wq, &wait, action, mode);
421}
422EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
423
424int __sched
425__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
426 wait_bit_action_f *action, unsigned mode)
427{
428 do {
429 int ret;
430
431 prepare_to_wait_exclusive(wq, &q->wait, mode);
432 if (!test_bit(q->key.bit_nr, q->key.flags))
433 continue;
434 ret = action(&q->key, mode);
435 if (!ret)
436 continue;
437 abort_exclusive_wait(wq, &q->wait, mode, &q->key);
438 return ret;
439 } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
440 finish_wait(wq, &q->wait);
441 return 0;
442}
443EXPORT_SYMBOL(__wait_on_bit_lock);
444
445int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
446 wait_bit_action_f *action, unsigned mode)
447{
448 wait_queue_head_t *wq = bit_waitqueue(word, bit);
449 DEFINE_WAIT_BIT(wait, word, bit);
450
451 return __wait_on_bit_lock(wq, &wait, action, mode);
452}
453EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
454
455void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
456{
457 struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
458 if (waitqueue_active(wq))
459 __wake_up(wq, TASK_NORMAL, 1, &key);
460}
461EXPORT_SYMBOL(__wake_up_bit);
462
463/**
464 * wake_up_bit - wake up a waiter on a bit
465 * @word: the word being waited on, a kernel virtual address
466 * @bit: the bit of the word being waited on
467 *
468 * There is a standard hashed waitqueue table for generic use. This
469 * is the part of the hashtable's accessor API that wakes up waiters
470 * on a bit. For instance, if one were to have waiters on a bitflag,
471 * one would call wake_up_bit() after clearing the bit.
472 *
473 * In order for this to function properly, as it uses waitqueue_active()
474 * internally, some kind of memory barrier must be done prior to calling
475 * this. Typically, this will be smp_mb__after_atomic(), but in some
476 * cases where bitflags are manipulated non-atomically under a lock, one
477 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
478 * because spin_unlock() does not guarantee a memory barrier.
479 */
480void wake_up_bit(void *word, int bit)
481{
482 __wake_up_bit(bit_waitqueue(word, bit), word, bit);
483}
484EXPORT_SYMBOL(wake_up_bit);
485
486wait_queue_head_t *bit_waitqueue(void *word, int bit)
487{
488 const int shift = BITS_PER_LONG == 32 ? 5 : 6;
489 const struct zone *zone = page_zone(virt_to_page(word));
490 unsigned long val = (unsigned long)word << shift | bit;
491
492 return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
493}
494EXPORT_SYMBOL(bit_waitqueue);
495
496/*
497 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
498 * index (we're keying off bit -1, but that would produce a horrible hash
499 * value).
500 */
501static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
502{
503 if (BITS_PER_LONG == 64) {
504 unsigned long q = (unsigned long)p;
505 return bit_waitqueue((void *)(q & ~1), q & 1);
506 }
507 return bit_waitqueue(p, 0);
508}
509
510static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
511 void *arg)
512{
513 struct wait_bit_key *key = arg;
514 struct wait_bit_queue *wait_bit
515 = container_of(wait, struct wait_bit_queue, wait);
516 atomic_t *val = key->flags;
517
518 if (wait_bit->key.flags != key->flags ||
519 wait_bit->key.bit_nr != key->bit_nr ||
520 atomic_read(val) != 0)
521 return 0;
522 return autoremove_wake_function(wait, mode, sync, key);
523}
524
525/*
526 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
527 * the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
528 * return codes halt waiting and return.
529 */
530static __sched
531int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
532 int (*action)(atomic_t *), unsigned mode)
533{
534 atomic_t *val;
535 int ret = 0;
536
537 do {
538 prepare_to_wait(wq, &q->wait, mode);
539 val = q->key.flags;
540 if (atomic_read(val) == 0)
541 break;
542 ret = (*action)(val);
543 } while (!ret && atomic_read(val) != 0);
544 finish_wait(wq, &q->wait);
545 return ret;
546}
547
548#define DEFINE_WAIT_ATOMIC_T(name, p) \
549 struct wait_bit_queue name = { \
550 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
551 .wait = { \
552 .private = current, \
553 .func = wake_atomic_t_function, \
554 .task_list = \
555 LIST_HEAD_INIT((name).wait.task_list), \
556 }, \
557 }
558
559__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
560 unsigned mode)
561{
562 wait_queue_head_t *wq = atomic_t_waitqueue(p);
563 DEFINE_WAIT_ATOMIC_T(wait, p);
564
565 return __wait_on_atomic_t(wq, &wait, action, mode);
566}
567EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
568
569/**
570 * wake_up_atomic_t - Wake up a waiter on a atomic_t
571 * @p: The atomic_t being waited on, a kernel virtual address
572 *
573 * Wake up anyone waiting for the atomic_t to go to zero.
574 *
575 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
576 * check is done by the waiter's wake function, not the by the waker itself).
577 */
578void wake_up_atomic_t(atomic_t *p)
579{
580 __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
581}
582EXPORT_SYMBOL(wake_up_atomic_t);
583
584__sched int bit_wait(struct wait_bit_key *word, int mode)
585{
586 schedule();
587 if (signal_pending_state(mode, current))
588 return -EINTR;
589 return 0;
590}
591EXPORT_SYMBOL(bit_wait);
592
593__sched int bit_wait_io(struct wait_bit_key *word, int mode)
594{
595 io_schedule();
596 if (signal_pending_state(mode, current))
597 return -EINTR;
598 return 0;
599}
600EXPORT_SYMBOL(bit_wait_io);
601
602__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
603{
604 unsigned long now = READ_ONCE(jiffies);
605 if (time_after_eq(now, word->timeout))
606 return -EAGAIN;
607 schedule_timeout(word->timeout - now);
608 if (signal_pending_state(mode, current))
609 return -EINTR;
610 return 0;
611}
612EXPORT_SYMBOL_GPL(bit_wait_timeout);
613
614__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
615{
616 unsigned long now = READ_ONCE(jiffies);
617 if (time_after_eq(now, word->timeout))
618 return -EAGAIN;
619 io_schedule_timeout(word->timeout - now);
620 if (signal_pending_state(mode, current))
621 return -EINTR;
622 return 0;
623}
624EXPORT_SYMBOL_GPL(bit_wait_io_timeout);