Commit | Line | Data |
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457c8996 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
1da177e4 LT |
2 | /* |
3 | * Generic waiting primitives. | |
4 | * | |
6d49e352 | 5 | * (C) 2004 Nadia Yvette Chambers, Oracle |
1da177e4 | 6 | */ |
325ea10c | 7 | #include "sched.h" |
1da177e4 | 8 | |
9d9d676f | 9 | void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key) |
21d71f51 | 10 | { |
9d9d676f IM |
11 | spin_lock_init(&wq_head->lock); |
12 | lockdep_set_class_and_name(&wq_head->lock, key, name); | |
2055da97 | 13 | INIT_LIST_HEAD(&wq_head->head); |
21d71f51 | 14 | } |
eb4542b9 | 15 | |
2fc39111 | 16 | EXPORT_SYMBOL(__init_waitqueue_head); |
eb4542b9 | 17 | |
9d9d676f | 18 | void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
19 | { |
20 | unsigned long flags; | |
21 | ||
50816c48 | 22 | wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
9d9d676f | 23 | spin_lock_irqsave(&wq_head->lock, flags); |
c6b9d9a3 | 24 | __add_wait_queue(wq_head, wq_entry); |
9d9d676f | 25 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
26 | } |
27 | EXPORT_SYMBOL(add_wait_queue); | |
28 | ||
9d9d676f | 29 | void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
30 | { |
31 | unsigned long flags; | |
32 | ||
50816c48 | 33 | wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
9d9d676f IM |
34 | spin_lock_irqsave(&wq_head->lock, flags); |
35 | __add_wait_queue_entry_tail(wq_head, wq_entry); | |
36 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
1da177e4 LT |
37 | } |
38 | EXPORT_SYMBOL(add_wait_queue_exclusive); | |
39 | ||
9d9d676f | 40 | void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
41 | { |
42 | unsigned long flags; | |
43 | ||
9d9d676f IM |
44 | spin_lock_irqsave(&wq_head->lock, flags); |
45 | __remove_wait_queue(wq_head, wq_entry); | |
46 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
1da177e4 LT |
47 | } |
48 | EXPORT_SYMBOL(remove_wait_queue); | |
49 | ||
2554db91 TC |
50 | /* |
51 | * Scan threshold to break wait queue walk. | |
52 | * This allows a waker to take a break from holding the | |
53 | * wait queue lock during the wait queue walk. | |
54 | */ | |
55 | #define WAITQUEUE_WALK_BREAK_CNT 64 | |
1da177e4 | 56 | |
b4145872 PZ |
57 | /* |
58 | * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just | |
59 | * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve | |
60 | * number) then we wake all the non-exclusive tasks and one exclusive task. | |
61 | * | |
62 | * There are circumstances in which we can try to wake a task which has already | |
63 | * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns | |
64 | * zero in this (rare) case, and we handle it by continuing to scan the queue. | |
65 | */ | |
2554db91 TC |
66 | static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, |
67 | int nr_exclusive, int wake_flags, void *key, | |
68 | wait_queue_entry_t *bookmark) | |
b4145872 | 69 | { |
ac6424b9 | 70 | wait_queue_entry_t *curr, *next; |
2554db91 TC |
71 | int cnt = 0; |
72 | ||
e05a8e4d CH |
73 | lockdep_assert_held(&wq_head->lock); |
74 | ||
2554db91 TC |
75 | if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) { |
76 | curr = list_next_entry(bookmark, entry); | |
b4145872 | 77 | |
2554db91 TC |
78 | list_del(&bookmark->entry); |
79 | bookmark->flags = 0; | |
80 | } else | |
81 | curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry); | |
82 | ||
83 | if (&curr->entry == &wq_head->head) | |
84 | return nr_exclusive; | |
85 | ||
86 | list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) { | |
b4145872 | 87 | unsigned flags = curr->flags; |
2554db91 TC |
88 | int ret; |
89 | ||
90 | if (flags & WQ_FLAG_BOOKMARK) | |
91 | continue; | |
92 | ||
93 | ret = curr->func(curr, mode, wake_flags, key); | |
3510ca20 LT |
94 | if (ret < 0) |
95 | break; | |
96 | if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) | |
b4145872 | 97 | break; |
2554db91 TC |
98 | |
99 | if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) && | |
100 | (&next->entry != &wq_head->head)) { | |
101 | bookmark->flags = WQ_FLAG_BOOKMARK; | |
102 | list_add_tail(&bookmark->entry, &next->entry); | |
103 | break; | |
104 | } | |
105 | } | |
97fb7a0a | 106 | |
2554db91 TC |
107 | return nr_exclusive; |
108 | } | |
109 | ||
110 | static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, | |
111 | int nr_exclusive, int wake_flags, void *key) | |
112 | { | |
113 | unsigned long flags; | |
114 | wait_queue_entry_t bookmark; | |
115 | ||
116 | bookmark.flags = 0; | |
117 | bookmark.private = NULL; | |
118 | bookmark.func = NULL; | |
119 | INIT_LIST_HEAD(&bookmark.entry); | |
120 | ||
016190a4 | 121 | do { |
2554db91 TC |
122 | spin_lock_irqsave(&wq_head->lock, flags); |
123 | nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, | |
124 | wake_flags, key, &bookmark); | |
125 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
016190a4 | 126 | } while (bookmark.flags & WQ_FLAG_BOOKMARK); |
b4145872 PZ |
127 | } |
128 | ||
129 | /** | |
130 | * __wake_up - wake up threads blocked on a waitqueue. | |
9d9d676f | 131 | * @wq_head: the waitqueue |
b4145872 PZ |
132 | * @mode: which threads |
133 | * @nr_exclusive: how many wake-one or wake-many threads to wake up | |
134 | * @key: is directly passed to the wakeup function | |
135 | * | |
7696f991 AP |
136 | * If this function wakes up a task, it executes a full memory barrier before |
137 | * accessing the task state. | |
b4145872 | 138 | */ |
9d9d676f | 139 | void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, |
b4145872 PZ |
140 | int nr_exclusive, void *key) |
141 | { | |
2554db91 | 142 | __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key); |
b4145872 PZ |
143 | } |
144 | EXPORT_SYMBOL(__wake_up); | |
145 | ||
146 | /* | |
147 | * Same as __wake_up but called with the spinlock in wait_queue_head_t held. | |
148 | */ | |
9d9d676f | 149 | void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr) |
b4145872 | 150 | { |
2554db91 | 151 | __wake_up_common(wq_head, mode, nr, 0, NULL, NULL); |
b4145872 PZ |
152 | } |
153 | EXPORT_SYMBOL_GPL(__wake_up_locked); | |
154 | ||
9d9d676f | 155 | void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key) |
b4145872 | 156 | { |
2554db91 | 157 | __wake_up_common(wq_head, mode, 1, 0, key, NULL); |
b4145872 PZ |
158 | } |
159 | EXPORT_SYMBOL_GPL(__wake_up_locked_key); | |
160 | ||
11a19c7b TC |
161 | void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head, |
162 | unsigned int mode, void *key, wait_queue_entry_t *bookmark) | |
163 | { | |
164 | __wake_up_common(wq_head, mode, 1, 0, key, bookmark); | |
165 | } | |
166 | EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark); | |
167 | ||
b4145872 PZ |
168 | /** |
169 | * __wake_up_sync_key - wake up threads blocked on a waitqueue. | |
9d9d676f | 170 | * @wq_head: the waitqueue |
b4145872 PZ |
171 | * @mode: which threads |
172 | * @nr_exclusive: how many wake-one or wake-many threads to wake up | |
173 | * @key: opaque value to be passed to wakeup targets | |
174 | * | |
175 | * The sync wakeup differs that the waker knows that it will schedule | |
176 | * away soon, so while the target thread will be woken up, it will not | |
177 | * be migrated to another CPU - ie. the two threads are 'synchronized' | |
178 | * with each other. This can prevent needless bouncing between CPUs. | |
179 | * | |
180 | * On UP it can prevent extra preemption. | |
181 | * | |
7696f991 AP |
182 | * If this function wakes up a task, it executes a full memory barrier before |
183 | * accessing the task state. | |
b4145872 | 184 | */ |
9d9d676f | 185 | void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, |
b4145872 PZ |
186 | int nr_exclusive, void *key) |
187 | { | |
b4145872 PZ |
188 | int wake_flags = 1; /* XXX WF_SYNC */ |
189 | ||
9d9d676f | 190 | if (unlikely(!wq_head)) |
b4145872 PZ |
191 | return; |
192 | ||
193 | if (unlikely(nr_exclusive != 1)) | |
194 | wake_flags = 0; | |
195 | ||
2554db91 | 196 | __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key); |
b4145872 PZ |
197 | } |
198 | EXPORT_SYMBOL_GPL(__wake_up_sync_key); | |
199 | ||
200 | /* | |
201 | * __wake_up_sync - see __wake_up_sync_key() | |
202 | */ | |
9d9d676f | 203 | void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive) |
b4145872 | 204 | { |
9d9d676f | 205 | __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL); |
b4145872 PZ |
206 | } |
207 | EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ | |
208 | ||
1da177e4 LT |
209 | /* |
210 | * Note: we use "set_current_state()" _after_ the wait-queue add, | |
211 | * because we need a memory barrier there on SMP, so that any | |
212 | * wake-function that tests for the wait-queue being active | |
213 | * will be guaranteed to see waitqueue addition _or_ subsequent | |
214 | * tests in this thread will see the wakeup having taken place. | |
215 | * | |
216 | * The spin_unlock() itself is semi-permeable and only protects | |
217 | * one way (it only protects stuff inside the critical region and | |
218 | * stops them from bleeding out - it would still allow subsequent | |
59c51591 | 219 | * loads to move into the critical region). |
1da177e4 | 220 | */ |
7ad5b3a5 | 221 | void |
9d9d676f | 222 | prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
1da177e4 LT |
223 | { |
224 | unsigned long flags; | |
225 | ||
50816c48 | 226 | wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
9d9d676f | 227 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 228 | if (list_empty(&wq_entry->entry)) |
9d9d676f | 229 | __add_wait_queue(wq_head, wq_entry); |
a25d644f | 230 | set_current_state(state); |
9d9d676f | 231 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
232 | } |
233 | EXPORT_SYMBOL(prepare_to_wait); | |
234 | ||
7ad5b3a5 | 235 | void |
9d9d676f | 236 | prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
1da177e4 LT |
237 | { |
238 | unsigned long flags; | |
239 | ||
50816c48 | 240 | wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
9d9d676f | 241 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 242 | if (list_empty(&wq_entry->entry)) |
9d9d676f | 243 | __add_wait_queue_entry_tail(wq_head, wq_entry); |
a25d644f | 244 | set_current_state(state); |
9d9d676f | 245 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
246 | } |
247 | EXPORT_SYMBOL(prepare_to_wait_exclusive); | |
248 | ||
50816c48 | 249 | void init_wait_entry(struct wait_queue_entry *wq_entry, int flags) |
0176beaf | 250 | { |
50816c48 IM |
251 | wq_entry->flags = flags; |
252 | wq_entry->private = current; | |
253 | wq_entry->func = autoremove_wake_function; | |
2055da97 | 254 | INIT_LIST_HEAD(&wq_entry->entry); |
0176beaf ON |
255 | } |
256 | EXPORT_SYMBOL(init_wait_entry); | |
257 | ||
9d9d676f | 258 | long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
c2d81644 ON |
259 | { |
260 | unsigned long flags; | |
b1ea06a9 | 261 | long ret = 0; |
c2d81644 | 262 | |
9d9d676f | 263 | spin_lock_irqsave(&wq_head->lock, flags); |
34ec35ad | 264 | if (signal_pending_state(state, current)) { |
b1ea06a9 ON |
265 | /* |
266 | * Exclusive waiter must not fail if it was selected by wakeup, | |
267 | * it should "consume" the condition we were waiting for. | |
268 | * | |
269 | * The caller will recheck the condition and return success if | |
270 | * we were already woken up, we can not miss the event because | |
9d9d676f | 271 | * wakeup locks/unlocks the same wq_head->lock. |
b1ea06a9 ON |
272 | * |
273 | * But we need to ensure that set-condition + wakeup after that | |
274 | * can't see us, it should wake up another exclusive waiter if | |
275 | * we fail. | |
276 | */ | |
2055da97 | 277 | list_del_init(&wq_entry->entry); |
b1ea06a9 ON |
278 | ret = -ERESTARTSYS; |
279 | } else { | |
2055da97 | 280 | if (list_empty(&wq_entry->entry)) { |
50816c48 | 281 | if (wq_entry->flags & WQ_FLAG_EXCLUSIVE) |
9d9d676f | 282 | __add_wait_queue_entry_tail(wq_head, wq_entry); |
b1ea06a9 | 283 | else |
9d9d676f | 284 | __add_wait_queue(wq_head, wq_entry); |
b1ea06a9 ON |
285 | } |
286 | set_current_state(state); | |
c2d81644 | 287 | } |
9d9d676f | 288 | spin_unlock_irqrestore(&wq_head->lock, flags); |
c2d81644 | 289 | |
b1ea06a9 | 290 | return ret; |
c2d81644 ON |
291 | } |
292 | EXPORT_SYMBOL(prepare_to_wait_event); | |
293 | ||
bd0f9b35 LT |
294 | /* |
295 | * Note! These two wait functions are entered with the | |
296 | * wait-queue lock held (and interrupts off in the _irq | |
297 | * case), so there is no race with testing the wakeup | |
298 | * condition in the caller before they add the wait | |
299 | * entry to the wake queue. | |
300 | */ | |
ac6424b9 | 301 | int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
bd0f9b35 | 302 | { |
2055da97 | 303 | if (likely(list_empty(&wait->entry))) |
ac6424b9 | 304 | __add_wait_queue_entry_tail(wq, wait); |
bd0f9b35 LT |
305 | |
306 | set_current_state(TASK_INTERRUPTIBLE); | |
307 | if (signal_pending(current)) | |
308 | return -ERESTARTSYS; | |
309 | ||
310 | spin_unlock(&wq->lock); | |
311 | schedule(); | |
312 | spin_lock(&wq->lock); | |
97fb7a0a | 313 | |
bd0f9b35 LT |
314 | return 0; |
315 | } | |
316 | EXPORT_SYMBOL(do_wait_intr); | |
317 | ||
ac6424b9 | 318 | int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
bd0f9b35 | 319 | { |
2055da97 | 320 | if (likely(list_empty(&wait->entry))) |
ac6424b9 | 321 | __add_wait_queue_entry_tail(wq, wait); |
bd0f9b35 LT |
322 | |
323 | set_current_state(TASK_INTERRUPTIBLE); | |
324 | if (signal_pending(current)) | |
325 | return -ERESTARTSYS; | |
326 | ||
327 | spin_unlock_irq(&wq->lock); | |
328 | schedule(); | |
329 | spin_lock_irq(&wq->lock); | |
97fb7a0a | 330 | |
bd0f9b35 LT |
331 | return 0; |
332 | } | |
333 | EXPORT_SYMBOL(do_wait_intr_irq); | |
334 | ||
ee2f154a | 335 | /** |
777c6c5f | 336 | * finish_wait - clean up after waiting in a queue |
9d9d676f | 337 | * @wq_head: waitqueue waited on |
50816c48 | 338 | * @wq_entry: wait descriptor |
777c6c5f JW |
339 | * |
340 | * Sets current thread back to running state and removes | |
341 | * the wait descriptor from the given waitqueue if still | |
342 | * queued. | |
343 | */ | |
9d9d676f | 344 | void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
345 | { |
346 | unsigned long flags; | |
347 | ||
348 | __set_current_state(TASK_RUNNING); | |
349 | /* | |
350 | * We can check for list emptiness outside the lock | |
351 | * IFF: | |
352 | * - we use the "careful" check that verifies both | |
353 | * the next and prev pointers, so that there cannot | |
354 | * be any half-pending updates in progress on other | |
355 | * CPU's that we haven't seen yet (and that might | |
356 | * still change the stack area. | |
357 | * and | |
358 | * - all other users take the lock (ie we can only | |
359 | * have _one_ other CPU that looks at or modifies | |
360 | * the list). | |
361 | */ | |
2055da97 | 362 | if (!list_empty_careful(&wq_entry->entry)) { |
9d9d676f | 363 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 364 | list_del_init(&wq_entry->entry); |
9d9d676f | 365 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
366 | } |
367 | } | |
368 | EXPORT_SYMBOL(finish_wait); | |
369 | ||
50816c48 | 370 | int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
1da177e4 | 371 | { |
50816c48 | 372 | int ret = default_wake_function(wq_entry, mode, sync, key); |
1da177e4 LT |
373 | |
374 | if (ret) | |
2055da97 | 375 | list_del_init(&wq_entry->entry); |
97fb7a0a | 376 | |
1da177e4 LT |
377 | return ret; |
378 | } | |
379 | EXPORT_SYMBOL(autoremove_wake_function); | |
380 | ||
cb6538e7 PZ |
381 | static inline bool is_kthread_should_stop(void) |
382 | { | |
383 | return (current->flags & PF_KTHREAD) && kthread_should_stop(); | |
384 | } | |
61ada528 PZ |
385 | |
386 | /* | |
387 | * DEFINE_WAIT_FUNC(wait, woken_wake_func); | |
388 | * | |
9d9d676f | 389 | * add_wait_queue(&wq_head, &wait); |
61ada528 PZ |
390 | * for (;;) { |
391 | * if (condition) | |
392 | * break; | |
393 | * | |
76e079fe | 394 | * // in wait_woken() // in woken_wake_function() |
61ada528 | 395 | * |
76e079fe AP |
396 | * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN; |
397 | * smp_mb(); // A try_to_wake_up(): | |
398 | * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier> | |
399 | * schedule() if (p->state & mode) | |
400 | * p->state = TASK_RUNNING; p->state = TASK_RUNNING; | |
401 | * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~ | |
402 | * smp_mb(); // B condition = true; | |
403 | * } smp_mb(); // C | |
404 | * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN; | |
61ada528 | 405 | */ |
50816c48 | 406 | long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) |
61ada528 | 407 | { |
61ada528 | 408 | /* |
76e079fe AP |
409 | * The below executes an smp_mb(), which matches with the full barrier |
410 | * executed by the try_to_wake_up() in woken_wake_function() such that | |
411 | * either we see the store to wq_entry->flags in woken_wake_function() | |
412 | * or woken_wake_function() sees our store to current->state. | |
61ada528 | 413 | */ |
76e079fe | 414 | set_current_state(mode); /* A */ |
50816c48 | 415 | if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) |
61ada528 PZ |
416 | timeout = schedule_timeout(timeout); |
417 | __set_current_state(TASK_RUNNING); | |
418 | ||
419 | /* | |
76e079fe AP |
420 | * The below executes an smp_mb(), which matches with the smp_mb() (C) |
421 | * in woken_wake_function() such that either we see the wait condition | |
422 | * being true or the store to wq_entry->flags in woken_wake_function() | |
423 | * follows ours in the coherence order. | |
61ada528 | 424 | */ |
50816c48 | 425 | smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */ |
61ada528 PZ |
426 | |
427 | return timeout; | |
428 | } | |
429 | EXPORT_SYMBOL(wait_woken); | |
430 | ||
50816c48 | 431 | int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
61ada528 | 432 | { |
76e079fe AP |
433 | /* Pairs with the smp_store_mb() in wait_woken(). */ |
434 | smp_mb(); /* C */ | |
50816c48 | 435 | wq_entry->flags |= WQ_FLAG_WOKEN; |
61ada528 | 436 | |
50816c48 | 437 | return default_wake_function(wq_entry, mode, sync, key); |
61ada528 PZ |
438 | } |
439 | EXPORT_SYMBOL(woken_wake_function); |