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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
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);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic waiting primitives.
4 *
5 * (C) 2004 Nadia Yvette Chambers, Oracle
6 */
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 add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
40{
41 unsigned long flags;
42
43 wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
44 spin_lock_irqsave(&wq_head->lock, flags);
45 __add_wait_queue(wq_head, wq_entry);
46 spin_unlock_irqrestore(&wq_head->lock, flags);
47}
48EXPORT_SYMBOL_GPL(add_wait_queue_priority);
49
50void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
51{
52 unsigned long flags;
53
54 spin_lock_irqsave(&wq_head->lock, flags);
55 __remove_wait_queue(wq_head, wq_entry);
56 spin_unlock_irqrestore(&wq_head->lock, flags);
57}
58EXPORT_SYMBOL(remove_wait_queue);
59
60/*
61 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
62 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
63 * number) then we wake that number of exclusive tasks, and potentially all
64 * the non-exclusive tasks. Normally, exclusive tasks will be at the end of
65 * the list and any non-exclusive tasks will be woken first. A priority task
66 * may be at the head of the list, and can consume the event without any other
67 * tasks being woken.
68 *
69 * There are circumstances in which we can try to wake a task which has already
70 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
71 * zero in this (rare) case, and we handle it by continuing to scan the queue.
72 */
73static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
74 int nr_exclusive, int wake_flags, void *key)
75{
76 wait_queue_entry_t *curr, *next;
77
78 lockdep_assert_held(&wq_head->lock);
79
80 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
81
82 if (&curr->entry == &wq_head->head)
83 return nr_exclusive;
84
85 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
86 unsigned flags = curr->flags;
87 int ret;
88
89 ret = curr->func(curr, mode, wake_flags, key);
90 if (ret < 0)
91 break;
92 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
93 break;
94 }
95
96 return nr_exclusive;
97}
98
99static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
100 int nr_exclusive, int wake_flags, void *key)
101{
102 unsigned long flags;
103 int remaining;
104
105 spin_lock_irqsave(&wq_head->lock, flags);
106 remaining = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags,
107 key);
108 spin_unlock_irqrestore(&wq_head->lock, flags);
109
110 return nr_exclusive - remaining;
111}
112
113/**
114 * __wake_up - wake up threads blocked on a waitqueue.
115 * @wq_head: the waitqueue
116 * @mode: which threads
117 * @nr_exclusive: how many wake-one or wake-many threads to wake up
118 * @key: is directly passed to the wakeup function
119 *
120 * If this function wakes up a task, it executes a full memory barrier
121 * before accessing the task state. Returns the number of exclusive
122 * tasks that were awaken.
123 */
124int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
125 int nr_exclusive, void *key)
126{
127 return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
128}
129EXPORT_SYMBOL(__wake_up);
130
131void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key)
132{
133 __wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key);
134}
135
136/*
137 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
138 */
139void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
140{
141 __wake_up_common(wq_head, mode, nr, 0, NULL);
142}
143EXPORT_SYMBOL_GPL(__wake_up_locked);
144
145void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
146{
147 __wake_up_common(wq_head, mode, 1, 0, key);
148}
149EXPORT_SYMBOL_GPL(__wake_up_locked_key);
150
151/**
152 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
153 * @wq_head: the waitqueue
154 * @mode: which threads
155 * @key: opaque value to be passed to wakeup targets
156 *
157 * The sync wakeup differs that the waker knows that it will schedule
158 * away soon, so while the target thread will be woken up, it will not
159 * be migrated to another CPU - ie. the two threads are 'synchronized'
160 * with each other. This can prevent needless bouncing between CPUs.
161 *
162 * On UP it can prevent extra preemption.
163 *
164 * If this function wakes up a task, it executes a full memory barrier before
165 * accessing the task state.
166 */
167void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
168 void *key)
169{
170 if (unlikely(!wq_head))
171 return;
172
173 __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
174}
175EXPORT_SYMBOL_GPL(__wake_up_sync_key);
176
177/**
178 * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
179 * @wq_head: the waitqueue
180 * @mode: which threads
181 * @key: opaque value to be passed to wakeup targets
182 *
183 * The sync wakeup differs in that the waker knows that it will schedule
184 * away soon, so while the target thread will be woken up, it will not
185 * be migrated to another CPU - ie. the two threads are 'synchronized'
186 * with each other. This can prevent needless bouncing between CPUs.
187 *
188 * On UP it can prevent extra preemption.
189 *
190 * If this function wakes up a task, it executes a full memory barrier before
191 * accessing the task state.
192 */
193void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
194 unsigned int mode, void *key)
195{
196 __wake_up_common(wq_head, mode, 1, WF_SYNC, key);
197}
198EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
199
200/*
201 * __wake_up_sync - see __wake_up_sync_key()
202 */
203void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
204{
205 __wake_up_sync_key(wq_head, mode, NULL);
206}
207EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
208
209void __wake_up_pollfree(struct wait_queue_head *wq_head)
210{
211 __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
212 /* POLLFREE must have cleared the queue. */
213 WARN_ON_ONCE(waitqueue_active(wq_head));
214}
215
216/*
217 * Note: we use "set_current_state()" _after_ the wait-queue add,
218 * because we need a memory barrier there on SMP, so that any
219 * wake-function that tests for the wait-queue being active
220 * will be guaranteed to see waitqueue addition _or_ subsequent
221 * tests in this thread will see the wakeup having taken place.
222 *
223 * The spin_unlock() itself is semi-permeable and only protects
224 * one way (it only protects stuff inside the critical region and
225 * stops them from bleeding out - it would still allow subsequent
226 * loads to move into the critical region).
227 */
228void
229prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
230{
231 unsigned long flags;
232
233 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
234 spin_lock_irqsave(&wq_head->lock, flags);
235 if (list_empty(&wq_entry->entry))
236 __add_wait_queue(wq_head, wq_entry);
237 set_current_state(state);
238 spin_unlock_irqrestore(&wq_head->lock, flags);
239}
240EXPORT_SYMBOL(prepare_to_wait);
241
242/* Returns true if we are the first waiter in the queue, false otherwise. */
243bool
244prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
245{
246 unsigned long flags;
247 bool was_empty = false;
248
249 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
250 spin_lock_irqsave(&wq_head->lock, flags);
251 if (list_empty(&wq_entry->entry)) {
252 was_empty = list_empty(&wq_head->head);
253 __add_wait_queue_entry_tail(wq_head, wq_entry);
254 }
255 set_current_state(state);
256 spin_unlock_irqrestore(&wq_head->lock, flags);
257 return was_empty;
258}
259EXPORT_SYMBOL(prepare_to_wait_exclusive);
260
261void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
262{
263 wq_entry->flags = flags;
264 wq_entry->private = current;
265 wq_entry->func = autoremove_wake_function;
266 INIT_LIST_HEAD(&wq_entry->entry);
267}
268EXPORT_SYMBOL(init_wait_entry);
269
270long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
271{
272 unsigned long flags;
273 long ret = 0;
274
275 spin_lock_irqsave(&wq_head->lock, flags);
276 if (signal_pending_state(state, current)) {
277 /*
278 * Exclusive waiter must not fail if it was selected by wakeup,
279 * it should "consume" the condition we were waiting for.
280 *
281 * The caller will recheck the condition and return success if
282 * we were already woken up, we can not miss the event because
283 * wakeup locks/unlocks the same wq_head->lock.
284 *
285 * But we need to ensure that set-condition + wakeup after that
286 * can't see us, it should wake up another exclusive waiter if
287 * we fail.
288 */
289 list_del_init(&wq_entry->entry);
290 ret = -ERESTARTSYS;
291 } else {
292 if (list_empty(&wq_entry->entry)) {
293 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
294 __add_wait_queue_entry_tail(wq_head, wq_entry);
295 else
296 __add_wait_queue(wq_head, wq_entry);
297 }
298 set_current_state(state);
299 }
300 spin_unlock_irqrestore(&wq_head->lock, flags);
301
302 return ret;
303}
304EXPORT_SYMBOL(prepare_to_wait_event);
305
306/*
307 * Note! These two wait functions are entered with the
308 * wait-queue lock held (and interrupts off in the _irq
309 * case), so there is no race with testing the wakeup
310 * condition in the caller before they add the wait
311 * entry to the wake queue.
312 */
313int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
314{
315 if (likely(list_empty(&wait->entry)))
316 __add_wait_queue_entry_tail(wq, wait);
317
318 set_current_state(TASK_INTERRUPTIBLE);
319 if (signal_pending(current))
320 return -ERESTARTSYS;
321
322 spin_unlock(&wq->lock);
323 schedule();
324 spin_lock(&wq->lock);
325
326 return 0;
327}
328EXPORT_SYMBOL(do_wait_intr);
329
330int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
331{
332 if (likely(list_empty(&wait->entry)))
333 __add_wait_queue_entry_tail(wq, wait);
334
335 set_current_state(TASK_INTERRUPTIBLE);
336 if (signal_pending(current))
337 return -ERESTARTSYS;
338
339 spin_unlock_irq(&wq->lock);
340 schedule();
341 spin_lock_irq(&wq->lock);
342
343 return 0;
344}
345EXPORT_SYMBOL(do_wait_intr_irq);
346
347/**
348 * finish_wait - clean up after waiting in a queue
349 * @wq_head: waitqueue waited on
350 * @wq_entry: wait descriptor
351 *
352 * Sets current thread back to running state and removes
353 * the wait descriptor from the given waitqueue if still
354 * queued.
355 */
356void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
357{
358 unsigned long flags;
359
360 __set_current_state(TASK_RUNNING);
361 /*
362 * We can check for list emptiness outside the lock
363 * IFF:
364 * - we use the "careful" check that verifies both
365 * the next and prev pointers, so that there cannot
366 * be any half-pending updates in progress on other
367 * CPU's that we haven't seen yet (and that might
368 * still change the stack area.
369 * and
370 * - all other users take the lock (ie we can only
371 * have _one_ other CPU that looks at or modifies
372 * the list).
373 */
374 if (!list_empty_careful(&wq_entry->entry)) {
375 spin_lock_irqsave(&wq_head->lock, flags);
376 list_del_init(&wq_entry->entry);
377 spin_unlock_irqrestore(&wq_head->lock, flags);
378 }
379}
380EXPORT_SYMBOL(finish_wait);
381
382int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
383{
384 int ret = default_wake_function(wq_entry, mode, sync, key);
385
386 if (ret)
387 list_del_init_careful(&wq_entry->entry);
388
389 return ret;
390}
391EXPORT_SYMBOL(autoremove_wake_function);
392
393/*
394 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
395 *
396 * add_wait_queue(&wq_head, &wait);
397 * for (;;) {
398 * if (condition)
399 * break;
400 *
401 * // in wait_woken() // in woken_wake_function()
402 *
403 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
404 * smp_mb(); // A try_to_wake_up():
405 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
406 * schedule() if (p->state & mode)
407 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
408 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
409 * smp_mb(); // B condition = true;
410 * } smp_mb(); // C
411 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
412 */
413long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
414{
415 /*
416 * The below executes an smp_mb(), which matches with the full barrier
417 * executed by the try_to_wake_up() in woken_wake_function() such that
418 * either we see the store to wq_entry->flags in woken_wake_function()
419 * or woken_wake_function() sees our store to current->state.
420 */
421 set_current_state(mode); /* A */
422 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park())
423 timeout = schedule_timeout(timeout);
424 __set_current_state(TASK_RUNNING);
425
426 /*
427 * The below executes an smp_mb(), which matches with the smp_mb() (C)
428 * in woken_wake_function() such that either we see the wait condition
429 * being true or the store to wq_entry->flags in woken_wake_function()
430 * follows ours in the coherence order.
431 */
432 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
433
434 return timeout;
435}
436EXPORT_SYMBOL(wait_woken);
437
438int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
439{
440 /* Pairs with the smp_store_mb() in wait_woken(). */
441 smp_mb(); /* C */
442 wq_entry->flags |= WQ_FLAG_WOKEN;
443
444 return default_wake_function(wq_entry, mode, sync, key);
445}
446EXPORT_SYMBOL(woken_wake_function);