Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0-only
2 : /*
3 : * Generic waiting primitives.
4 : *
5 : * (C) 2004 Nadia Yvette Chambers, Oracle
6 : */
7 :
8 1902 : void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
9 : {
10 2158 : spin_lock_init(&wq_head->lock);
11 : lockdep_set_class_and_name(&wq_head->lock, key, name);
12 4316 : INIT_LIST_HEAD(&wq_head->head);
13 1902 : }
14 :
15 : EXPORT_SYMBOL(__init_waitqueue_head);
16 :
17 0 : void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
18 : {
19 : unsigned long flags;
20 :
21 0 : wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
22 0 : spin_lock_irqsave(&wq_head->lock, flags);
23 0 : __add_wait_queue(wq_head, wq_entry);
24 0 : spin_unlock_irqrestore(&wq_head->lock, flags);
25 0 : }
26 : EXPORT_SYMBOL(add_wait_queue);
27 :
28 0 : void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
29 : {
30 : unsigned long flags;
31 :
32 0 : wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
33 0 : spin_lock_irqsave(&wq_head->lock, flags);
34 0 : __add_wait_queue_entry_tail(wq_head, wq_entry);
35 0 : spin_unlock_irqrestore(&wq_head->lock, flags);
36 0 : }
37 : EXPORT_SYMBOL(add_wait_queue_exclusive);
38 :
39 0 : void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
40 : {
41 : unsigned long flags;
42 :
43 0 : wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
44 0 : spin_lock_irqsave(&wq_head->lock, flags);
45 0 : __add_wait_queue(wq_head, wq_entry);
46 0 : spin_unlock_irqrestore(&wq_head->lock, flags);
47 0 : }
48 : EXPORT_SYMBOL_GPL(add_wait_queue_priority);
49 :
50 0 : void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
51 : {
52 : unsigned long flags;
53 :
54 0 : spin_lock_irqsave(&wq_head->lock, flags);
55 0 : __remove_wait_queue(wq_head, wq_entry);
56 0 : spin_unlock_irqrestore(&wq_head->lock, flags);
57 0 : }
58 : EXPORT_SYMBOL(remove_wait_queue);
59 :
60 : /*
61 : * Scan threshold to break wait queue walk.
62 : * This allows a waker to take a break from holding the
63 : * wait queue lock during the wait queue walk.
64 : */
65 : #define WAITQUEUE_WALK_BREAK_CNT 64
66 :
67 : /*
68 : * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
69 : * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
70 : * number) then we wake that number of exclusive tasks, and potentially all
71 : * the non-exclusive tasks. Normally, exclusive tasks will be at the end of
72 : * the list and any non-exclusive tasks will be woken first. A priority task
73 : * may be at the head of the list, and can consume the event without any other
74 : * tasks being woken.
75 : *
76 : * There are circumstances in which we can try to wake a task which has already
77 : * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
78 : * zero in this (rare) case, and we handle it by continuing to scan the queue.
79 : */
80 670 : static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
81 : int nr_exclusive, int wake_flags, void *key,
82 : wait_queue_entry_t *bookmark)
83 : {
84 : wait_queue_entry_t *curr, *next;
85 670 : int cnt = 0;
86 :
87 : lockdep_assert_held(&wq_head->lock);
88 :
89 670 : if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
90 0 : curr = list_next_entry(bookmark, entry);
91 :
92 0 : list_del(&bookmark->entry);
93 0 : bookmark->flags = 0;
94 : } else
95 670 : curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
96 :
97 670 : if (&curr->entry == &wq_head->head)
98 : return nr_exclusive;
99 :
100 0 : list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
101 0 : unsigned flags = curr->flags;
102 : int ret;
103 :
104 0 : if (flags & WQ_FLAG_BOOKMARK)
105 0 : continue;
106 :
107 0 : ret = curr->func(curr, mode, wake_flags, key);
108 0 : if (ret < 0)
109 : break;
110 0 : if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
111 : break;
112 :
113 0 : if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
114 0 : (&next->entry != &wq_head->head)) {
115 0 : bookmark->flags = WQ_FLAG_BOOKMARK;
116 0 : list_add_tail(&bookmark->entry, &next->entry);
117 : break;
118 : }
119 : }
120 :
121 : return nr_exclusive;
122 : }
123 :
124 670 : static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
125 : int nr_exclusive, int wake_flags, void *key)
126 : {
127 : unsigned long flags;
128 : wait_queue_entry_t bookmark;
129 670 : int remaining = nr_exclusive;
130 :
131 670 : bookmark.flags = 0;
132 670 : bookmark.private = NULL;
133 670 : bookmark.func = NULL;
134 : INIT_LIST_HEAD(&bookmark.entry);
135 :
136 : do {
137 670 : spin_lock_irqsave(&wq_head->lock, flags);
138 670 : remaining = __wake_up_common(wq_head, mode, remaining,
139 : wake_flags, key, &bookmark);
140 1340 : spin_unlock_irqrestore(&wq_head->lock, flags);
141 670 : } while (bookmark.flags & WQ_FLAG_BOOKMARK);
142 :
143 670 : return nr_exclusive - remaining;
144 : }
145 :
146 : /**
147 : * __wake_up - wake up threads blocked on a waitqueue.
148 : * @wq_head: the waitqueue
149 : * @mode: which threads
150 : * @nr_exclusive: how many wake-one or wake-many threads to wake up
151 : * @key: is directly passed to the wakeup function
152 : *
153 : * If this function wakes up a task, it executes a full memory barrier
154 : * before accessing the task state. Returns the number of exclusive
155 : * tasks that were awaken.
156 : */
157 345 : int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
158 : int nr_exclusive, void *key)
159 : {
160 345 : return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
161 : }
162 : EXPORT_SYMBOL(__wake_up);
163 :
164 : /*
165 : * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
166 : */
167 0 : void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
168 : {
169 0 : __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
170 0 : }
171 : EXPORT_SYMBOL_GPL(__wake_up_locked);
172 :
173 0 : void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
174 : {
175 0 : __wake_up_common(wq_head, mode, 1, 0, key, NULL);
176 0 : }
177 : EXPORT_SYMBOL_GPL(__wake_up_locked_key);
178 :
179 0 : void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
180 : unsigned int mode, void *key, wait_queue_entry_t *bookmark)
181 : {
182 0 : __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
183 0 : }
184 : EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
185 :
186 : /**
187 : * __wake_up_sync_key - wake up threads blocked on a waitqueue.
188 : * @wq_head: the waitqueue
189 : * @mode: which threads
190 : * @key: opaque value to be passed to wakeup targets
191 : *
192 : * The sync wakeup differs that the waker knows that it will schedule
193 : * away soon, so while the target thread will be woken up, it will not
194 : * be migrated to another CPU - ie. the two threads are 'synchronized'
195 : * with each other. This can prevent needless bouncing between CPUs.
196 : *
197 : * On UP it can prevent extra preemption.
198 : *
199 : * If this function wakes up a task, it executes a full memory barrier before
200 : * accessing the task state.
201 : */
202 325 : void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
203 : void *key)
204 : {
205 325 : if (unlikely(!wq_head))
206 : return;
207 :
208 325 : __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
209 : }
210 : EXPORT_SYMBOL_GPL(__wake_up_sync_key);
211 :
212 : /**
213 : * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
214 : * @wq_head: the waitqueue
215 : * @mode: which threads
216 : * @key: opaque value to be passed to wakeup targets
217 : *
218 : * The sync wakeup differs in that the waker knows that it will schedule
219 : * away soon, so while the target thread will be woken up, it will not
220 : * be migrated to another CPU - ie. the two threads are 'synchronized'
221 : * with each other. This can prevent needless bouncing between CPUs.
222 : *
223 : * On UP it can prevent extra preemption.
224 : *
225 : * If this function wakes up a task, it executes a full memory barrier before
226 : * accessing the task state.
227 : */
228 0 : void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
229 : unsigned int mode, void *key)
230 : {
231 0 : __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
232 0 : }
233 : EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
234 :
235 : /*
236 : * __wake_up_sync - see __wake_up_sync_key()
237 : */
238 0 : void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
239 : {
240 0 : __wake_up_sync_key(wq_head, mode, NULL);
241 0 : }
242 : EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
243 :
244 0 : void __wake_up_pollfree(struct wait_queue_head *wq_head)
245 : {
246 0 : __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
247 : /* POLLFREE must have cleared the queue. */
248 0 : WARN_ON_ONCE(waitqueue_active(wq_head));
249 0 : }
250 :
251 : /*
252 : * Note: we use "set_current_state()" _after_ the wait-queue add,
253 : * because we need a memory barrier there on SMP, so that any
254 : * wake-function that tests for the wait-queue being active
255 : * will be guaranteed to see waitqueue addition _or_ subsequent
256 : * tests in this thread will see the wakeup having taken place.
257 : *
258 : * The spin_unlock() itself is semi-permeable and only protects
259 : * one way (it only protects stuff inside the critical region and
260 : * stops them from bleeding out - it would still allow subsequent
261 : * loads to move into the critical region).
262 : */
263 : void
264 2 : prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
265 : {
266 : unsigned long flags;
267 :
268 2 : wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
269 2 : spin_lock_irqsave(&wq_head->lock, flags);
270 4 : if (list_empty(&wq_entry->entry))
271 : __add_wait_queue(wq_head, wq_entry);
272 2 : set_current_state(state);
273 4 : spin_unlock_irqrestore(&wq_head->lock, flags);
274 2 : }
275 : EXPORT_SYMBOL(prepare_to_wait);
276 :
277 : /* Returns true if we are the first waiter in the queue, false otherwise. */
278 : bool
279 0 : prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
280 : {
281 : unsigned long flags;
282 0 : bool was_empty = false;
283 :
284 0 : wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
285 0 : spin_lock_irqsave(&wq_head->lock, flags);
286 0 : if (list_empty(&wq_entry->entry)) {
287 0 : was_empty = list_empty(&wq_head->head);
288 : __add_wait_queue_entry_tail(wq_head, wq_entry);
289 : }
290 0 : set_current_state(state);
291 0 : spin_unlock_irqrestore(&wq_head->lock, flags);
292 0 : return was_empty;
293 : }
294 : EXPORT_SYMBOL(prepare_to_wait_exclusive);
295 :
296 53 : void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
297 : {
298 53 : wq_entry->flags = flags;
299 53 : wq_entry->private = current;
300 53 : wq_entry->func = autoremove_wake_function;
301 106 : INIT_LIST_HEAD(&wq_entry->entry);
302 53 : }
303 : EXPORT_SYMBOL(init_wait_entry);
304 :
305 104 : long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
306 : {
307 : unsigned long flags;
308 104 : long ret = 0;
309 :
310 104 : spin_lock_irqsave(&wq_head->lock, flags);
311 104 : if (signal_pending_state(state, current)) {
312 : /*
313 : * Exclusive waiter must not fail if it was selected by wakeup,
314 : * it should "consume" the condition we were waiting for.
315 : *
316 : * The caller will recheck the condition and return success if
317 : * we were already woken up, we can not miss the event because
318 : * wakeup locks/unlocks the same wq_head->lock.
319 : *
320 : * But we need to ensure that set-condition + wakeup after that
321 : * can't see us, it should wake up another exclusive waiter if
322 : * we fail.
323 : */
324 0 : list_del_init(&wq_entry->entry);
325 0 : ret = -ERESTARTSYS;
326 : } else {
327 208 : if (list_empty(&wq_entry->entry)) {
328 53 : if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
329 : __add_wait_queue_entry_tail(wq_head, wq_entry);
330 : else
331 : __add_wait_queue(wq_head, wq_entry);
332 : }
333 104 : set_current_state(state);
334 : }
335 208 : spin_unlock_irqrestore(&wq_head->lock, flags);
336 :
337 104 : return ret;
338 : }
339 : EXPORT_SYMBOL(prepare_to_wait_event);
340 :
341 : /*
342 : * Note! These two wait functions are entered with the
343 : * wait-queue lock held (and interrupts off in the _irq
344 : * case), so there is no race with testing the wakeup
345 : * condition in the caller before they add the wait
346 : * entry to the wake queue.
347 : */
348 0 : int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
349 : {
350 0 : if (likely(list_empty(&wait->entry)))
351 : __add_wait_queue_entry_tail(wq, wait);
352 :
353 0 : set_current_state(TASK_INTERRUPTIBLE);
354 0 : if (signal_pending(current))
355 : return -ERESTARTSYS;
356 :
357 0 : spin_unlock(&wq->lock);
358 0 : schedule();
359 0 : spin_lock(&wq->lock);
360 :
361 0 : return 0;
362 : }
363 : EXPORT_SYMBOL(do_wait_intr);
364 :
365 0 : int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
366 : {
367 0 : if (likely(list_empty(&wait->entry)))
368 : __add_wait_queue_entry_tail(wq, wait);
369 :
370 0 : set_current_state(TASK_INTERRUPTIBLE);
371 0 : if (signal_pending(current))
372 : return -ERESTARTSYS;
373 :
374 0 : spin_unlock_irq(&wq->lock);
375 0 : schedule();
376 0 : spin_lock_irq(&wq->lock);
377 :
378 0 : return 0;
379 : }
380 : EXPORT_SYMBOL(do_wait_intr_irq);
381 :
382 : /**
383 : * finish_wait - clean up after waiting in a queue
384 : * @wq_head: waitqueue waited on
385 : * @wq_entry: wait descriptor
386 : *
387 : * Sets current thread back to running state and removes
388 : * the wait descriptor from the given waitqueue if still
389 : * queued.
390 : */
391 52 : void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
392 : {
393 : unsigned long flags;
394 :
395 52 : __set_current_state(TASK_RUNNING);
396 : /*
397 : * We can check for list emptiness outside the lock
398 : * IFF:
399 : * - we use the "careful" check that verifies both
400 : * the next and prev pointers, so that there cannot
401 : * be any half-pending updates in progress on other
402 : * CPU's that we haven't seen yet (and that might
403 : * still change the stack area.
404 : * and
405 : * - all other users take the lock (ie we can only
406 : * have _one_ other CPU that looks at or modifies
407 : * the list).
408 : */
409 104 : if (!list_empty_careful(&wq_entry->entry)) {
410 52 : spin_lock_irqsave(&wq_head->lock, flags);
411 104 : list_del_init(&wq_entry->entry);
412 52 : spin_unlock_irqrestore(&wq_head->lock, flags);
413 : }
414 52 : }
415 : EXPORT_SYMBOL(finish_wait);
416 :
417 0 : int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
418 : {
419 0 : int ret = default_wake_function(wq_entry, mode, sync, key);
420 :
421 0 : if (ret)
422 0 : list_del_init_careful(&wq_entry->entry);
423 :
424 0 : return ret;
425 : }
426 : EXPORT_SYMBOL(autoremove_wake_function);
427 :
428 0 : static inline bool is_kthread_should_stop(void)
429 : {
430 0 : return (current->flags & PF_KTHREAD) && kthread_should_stop();
431 : }
432 :
433 : /*
434 : * DEFINE_WAIT_FUNC(wait, woken_wake_func);
435 : *
436 : * add_wait_queue(&wq_head, &wait);
437 : * for (;;) {
438 : * if (condition)
439 : * break;
440 : *
441 : * // in wait_woken() // in woken_wake_function()
442 : *
443 : * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
444 : * smp_mb(); // A try_to_wake_up():
445 : * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
446 : * schedule() if (p->state & mode)
447 : * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
448 : * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
449 : * smp_mb(); // B condition = true;
450 : * } smp_mb(); // C
451 : * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
452 : */
453 0 : long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
454 : {
455 : /*
456 : * The below executes an smp_mb(), which matches with the full barrier
457 : * executed by the try_to_wake_up() in woken_wake_function() such that
458 : * either we see the store to wq_entry->flags in woken_wake_function()
459 : * or woken_wake_function() sees our store to current->state.
460 : */
461 0 : set_current_state(mode); /* A */
462 0 : if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
463 0 : timeout = schedule_timeout(timeout);
464 0 : __set_current_state(TASK_RUNNING);
465 :
466 : /*
467 : * The below executes an smp_mb(), which matches with the smp_mb() (C)
468 : * in woken_wake_function() such that either we see the wait condition
469 : * being true or the store to wq_entry->flags in woken_wake_function()
470 : * follows ours in the coherence order.
471 : */
472 0 : smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
473 :
474 0 : return timeout;
475 : }
476 : EXPORT_SYMBOL(wait_woken);
477 :
478 0 : int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
479 : {
480 : /* Pairs with the smp_store_mb() in wait_woken(). */
481 0 : smp_mb(); /* C */
482 0 : wq_entry->flags |= WQ_FLAG_WOKEN;
483 :
484 0 : return default_wake_function(wq_entry, mode, sync, key);
485 : }
486 : EXPORT_SYMBOL(woken_wake_function);
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