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Commit | Line | Data |
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1da177e4 LT |
1 | /* |
2 | * Generic waiting primitives. | |
3 | * | |
6d49e352 | 4 | * (C) 2004 Nadia Yvette Chambers, Oracle |
1da177e4 | 5 | */ |
1da177e4 | 6 | #include <linux/init.h> |
9984de1a | 7 | #include <linux/export.h> |
174cd4b1 | 8 | #include <linux/sched/signal.h> |
b17b0153 | 9 | #include <linux/sched/debug.h> |
1da177e4 LT |
10 | #include <linux/mm.h> |
11 | #include <linux/wait.h> | |
12 | #include <linux/hash.h> | |
cb6538e7 | 13 | #include <linux/kthread.h> |
1da177e4 | 14 | |
9d9d676f | 15 | void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key) |
21d71f51 | 16 | { |
9d9d676f IM |
17 | spin_lock_init(&wq_head->lock); |
18 | lockdep_set_class_and_name(&wq_head->lock, key, name); | |
2055da97 | 19 | INIT_LIST_HEAD(&wq_head->head); |
21d71f51 | 20 | } |
eb4542b9 | 21 | |
2fc39111 | 22 | EXPORT_SYMBOL(__init_waitqueue_head); |
eb4542b9 | 23 | |
9d9d676f | 24 | void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
25 | { |
26 | unsigned long flags; | |
27 | ||
50816c48 | 28 | wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
9d9d676f IM |
29 | spin_lock_irqsave(&wq_head->lock, flags); |
30 | __add_wait_queue_entry_tail(wq_head, wq_entry); | |
31 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
1da177e4 LT |
32 | } |
33 | EXPORT_SYMBOL(add_wait_queue); | |
34 | ||
9d9d676f | 35 | void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
36 | { |
37 | unsigned long flags; | |
38 | ||
50816c48 | 39 | wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
9d9d676f IM |
40 | spin_lock_irqsave(&wq_head->lock, flags); |
41 | __add_wait_queue_entry_tail(wq_head, wq_entry); | |
42 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
1da177e4 LT |
43 | } |
44 | EXPORT_SYMBOL(add_wait_queue_exclusive); | |
45 | ||
9d9d676f | 46 | void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
47 | { |
48 | unsigned long flags; | |
49 | ||
9d9d676f IM |
50 | spin_lock_irqsave(&wq_head->lock, flags); |
51 | __remove_wait_queue(wq_head, wq_entry); | |
52 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
1da177e4 LT |
53 | } |
54 | EXPORT_SYMBOL(remove_wait_queue); | |
55 | ||
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 | */ | |
9d9d676f | 66 | static void __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, |
b4145872 PZ |
67 | int nr_exclusive, int wake_flags, void *key) |
68 | { | |
ac6424b9 | 69 | wait_queue_entry_t *curr, *next; |
b4145872 | 70 | |
2055da97 | 71 | list_for_each_entry_safe(curr, next, &wq_head->head, entry) { |
b4145872 | 72 | unsigned flags = curr->flags; |
3510ca20 LT |
73 | int ret = curr->func(curr, mode, wake_flags, key); |
74 | if (ret < 0) | |
75 | break; | |
76 | if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) | |
b4145872 PZ |
77 | break; |
78 | } | |
79 | } | |
80 | ||
81 | /** | |
82 | * __wake_up - wake up threads blocked on a waitqueue. | |
9d9d676f | 83 | * @wq_head: the waitqueue |
b4145872 PZ |
84 | * @mode: which threads |
85 | * @nr_exclusive: how many wake-one or wake-many threads to wake up | |
86 | * @key: is directly passed to the wakeup function | |
87 | * | |
88 | * It may be assumed that this function implies a write memory barrier before | |
89 | * changing the task state if and only if any tasks are woken up. | |
90 | */ | |
9d9d676f | 91 | void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, |
b4145872 PZ |
92 | int nr_exclusive, void *key) |
93 | { | |
94 | unsigned long flags; | |
95 | ||
9d9d676f IM |
96 | spin_lock_irqsave(&wq_head->lock, flags); |
97 | __wake_up_common(wq_head, mode, nr_exclusive, 0, key); | |
98 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
b4145872 PZ |
99 | } |
100 | EXPORT_SYMBOL(__wake_up); | |
101 | ||
102 | /* | |
103 | * Same as __wake_up but called with the spinlock in wait_queue_head_t held. | |
104 | */ | |
9d9d676f | 105 | void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr) |
b4145872 | 106 | { |
9d9d676f | 107 | __wake_up_common(wq_head, mode, nr, 0, NULL); |
b4145872 PZ |
108 | } |
109 | EXPORT_SYMBOL_GPL(__wake_up_locked); | |
110 | ||
9d9d676f | 111 | void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key) |
b4145872 | 112 | { |
9d9d676f | 113 | __wake_up_common(wq_head, mode, 1, 0, key); |
b4145872 PZ |
114 | } |
115 | EXPORT_SYMBOL_GPL(__wake_up_locked_key); | |
116 | ||
117 | /** | |
118 | * __wake_up_sync_key - wake up threads blocked on a waitqueue. | |
9d9d676f | 119 | * @wq_head: the waitqueue |
b4145872 PZ |
120 | * @mode: which threads |
121 | * @nr_exclusive: how many wake-one or wake-many threads to wake up | |
122 | * @key: opaque value to be passed to wakeup targets | |
123 | * | |
124 | * The sync wakeup differs that the waker knows that it will schedule | |
125 | * away soon, so while the target thread will be woken up, it will not | |
126 | * be migrated to another CPU - ie. the two threads are 'synchronized' | |
127 | * with each other. This can prevent needless bouncing between CPUs. | |
128 | * | |
129 | * On UP it can prevent extra preemption. | |
130 | * | |
131 | * It may be assumed that this function implies a write memory barrier before | |
132 | * changing the task state if and only if any tasks are woken up. | |
133 | */ | |
9d9d676f | 134 | void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, |
b4145872 PZ |
135 | int nr_exclusive, void *key) |
136 | { | |
137 | unsigned long flags; | |
138 | int wake_flags = 1; /* XXX WF_SYNC */ | |
139 | ||
9d9d676f | 140 | if (unlikely(!wq_head)) |
b4145872 PZ |
141 | return; |
142 | ||
143 | if (unlikely(nr_exclusive != 1)) | |
144 | wake_flags = 0; | |
145 | ||
9d9d676f IM |
146 | spin_lock_irqsave(&wq_head->lock, flags); |
147 | __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key); | |
148 | spin_unlock_irqrestore(&wq_head->lock, flags); | |
b4145872 PZ |
149 | } |
150 | EXPORT_SYMBOL_GPL(__wake_up_sync_key); | |
151 | ||
152 | /* | |
153 | * __wake_up_sync - see __wake_up_sync_key() | |
154 | */ | |
9d9d676f | 155 | void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive) |
b4145872 | 156 | { |
9d9d676f | 157 | __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL); |
b4145872 PZ |
158 | } |
159 | EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ | |
160 | ||
1da177e4 LT |
161 | /* |
162 | * Note: we use "set_current_state()" _after_ the wait-queue add, | |
163 | * because we need a memory barrier there on SMP, so that any | |
164 | * wake-function that tests for the wait-queue being active | |
165 | * will be guaranteed to see waitqueue addition _or_ subsequent | |
166 | * tests in this thread will see the wakeup having taken place. | |
167 | * | |
168 | * The spin_unlock() itself is semi-permeable and only protects | |
169 | * one way (it only protects stuff inside the critical region and | |
170 | * stops them from bleeding out - it would still allow subsequent | |
59c51591 | 171 | * loads to move into the critical region). |
1da177e4 | 172 | */ |
7ad5b3a5 | 173 | void |
9d9d676f | 174 | prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
1da177e4 LT |
175 | { |
176 | unsigned long flags; | |
177 | ||
50816c48 | 178 | wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
9d9d676f | 179 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 180 | if (list_empty(&wq_entry->entry)) |
9d9d676f | 181 | __add_wait_queue(wq_head, wq_entry); |
a25d644f | 182 | set_current_state(state); |
9d9d676f | 183 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
184 | } |
185 | EXPORT_SYMBOL(prepare_to_wait); | |
186 | ||
7ad5b3a5 | 187 | void |
9d9d676f | 188 | prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
1da177e4 LT |
189 | { |
190 | unsigned long flags; | |
191 | ||
50816c48 | 192 | wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
9d9d676f | 193 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 194 | if (list_empty(&wq_entry->entry)) |
9d9d676f | 195 | __add_wait_queue_entry_tail(wq_head, wq_entry); |
a25d644f | 196 | set_current_state(state); |
9d9d676f | 197 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
198 | } |
199 | EXPORT_SYMBOL(prepare_to_wait_exclusive); | |
200 | ||
50816c48 | 201 | void init_wait_entry(struct wait_queue_entry *wq_entry, int flags) |
0176beaf | 202 | { |
50816c48 IM |
203 | wq_entry->flags = flags; |
204 | wq_entry->private = current; | |
205 | wq_entry->func = autoremove_wake_function; | |
2055da97 | 206 | INIT_LIST_HEAD(&wq_entry->entry); |
0176beaf ON |
207 | } |
208 | EXPORT_SYMBOL(init_wait_entry); | |
209 | ||
9d9d676f | 210 | long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
c2d81644 ON |
211 | { |
212 | unsigned long flags; | |
b1ea06a9 | 213 | long ret = 0; |
c2d81644 | 214 | |
9d9d676f | 215 | spin_lock_irqsave(&wq_head->lock, flags); |
b1ea06a9 ON |
216 | if (unlikely(signal_pending_state(state, current))) { |
217 | /* | |
218 | * Exclusive waiter must not fail if it was selected by wakeup, | |
219 | * it should "consume" the condition we were waiting for. | |
220 | * | |
221 | * The caller will recheck the condition and return success if | |
222 | * we were already woken up, we can not miss the event because | |
9d9d676f | 223 | * wakeup locks/unlocks the same wq_head->lock. |
b1ea06a9 ON |
224 | * |
225 | * But we need to ensure that set-condition + wakeup after that | |
226 | * can't see us, it should wake up another exclusive waiter if | |
227 | * we fail. | |
228 | */ | |
2055da97 | 229 | list_del_init(&wq_entry->entry); |
b1ea06a9 ON |
230 | ret = -ERESTARTSYS; |
231 | } else { | |
2055da97 | 232 | if (list_empty(&wq_entry->entry)) { |
50816c48 | 233 | if (wq_entry->flags & WQ_FLAG_EXCLUSIVE) |
9d9d676f | 234 | __add_wait_queue_entry_tail(wq_head, wq_entry); |
b1ea06a9 | 235 | else |
9d9d676f | 236 | __add_wait_queue(wq_head, wq_entry); |
b1ea06a9 ON |
237 | } |
238 | set_current_state(state); | |
c2d81644 | 239 | } |
9d9d676f | 240 | spin_unlock_irqrestore(&wq_head->lock, flags); |
c2d81644 | 241 | |
b1ea06a9 | 242 | return ret; |
c2d81644 ON |
243 | } |
244 | EXPORT_SYMBOL(prepare_to_wait_event); | |
245 | ||
bd0f9b35 LT |
246 | /* |
247 | * Note! These two wait functions are entered with the | |
248 | * wait-queue lock held (and interrupts off in the _irq | |
249 | * case), so there is no race with testing the wakeup | |
250 | * condition in the caller before they add the wait | |
251 | * entry to the wake queue. | |
252 | */ | |
ac6424b9 | 253 | int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
bd0f9b35 | 254 | { |
2055da97 | 255 | if (likely(list_empty(&wait->entry))) |
ac6424b9 | 256 | __add_wait_queue_entry_tail(wq, wait); |
bd0f9b35 LT |
257 | |
258 | set_current_state(TASK_INTERRUPTIBLE); | |
259 | if (signal_pending(current)) | |
260 | return -ERESTARTSYS; | |
261 | ||
262 | spin_unlock(&wq->lock); | |
263 | schedule(); | |
264 | spin_lock(&wq->lock); | |
265 | return 0; | |
266 | } | |
267 | EXPORT_SYMBOL(do_wait_intr); | |
268 | ||
ac6424b9 | 269 | int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
bd0f9b35 | 270 | { |
2055da97 | 271 | if (likely(list_empty(&wait->entry))) |
ac6424b9 | 272 | __add_wait_queue_entry_tail(wq, wait); |
bd0f9b35 LT |
273 | |
274 | set_current_state(TASK_INTERRUPTIBLE); | |
275 | if (signal_pending(current)) | |
276 | return -ERESTARTSYS; | |
277 | ||
278 | spin_unlock_irq(&wq->lock); | |
279 | schedule(); | |
280 | spin_lock_irq(&wq->lock); | |
281 | return 0; | |
282 | } | |
283 | EXPORT_SYMBOL(do_wait_intr_irq); | |
284 | ||
ee2f154a | 285 | /** |
777c6c5f | 286 | * finish_wait - clean up after waiting in a queue |
9d9d676f | 287 | * @wq_head: waitqueue waited on |
50816c48 | 288 | * @wq_entry: wait descriptor |
777c6c5f JW |
289 | * |
290 | * Sets current thread back to running state and removes | |
291 | * the wait descriptor from the given waitqueue if still | |
292 | * queued. | |
293 | */ | |
9d9d676f | 294 | void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
1da177e4 LT |
295 | { |
296 | unsigned long flags; | |
297 | ||
298 | __set_current_state(TASK_RUNNING); | |
299 | /* | |
300 | * We can check for list emptiness outside the lock | |
301 | * IFF: | |
302 | * - we use the "careful" check that verifies both | |
303 | * the next and prev pointers, so that there cannot | |
304 | * be any half-pending updates in progress on other | |
305 | * CPU's that we haven't seen yet (and that might | |
306 | * still change the stack area. | |
307 | * and | |
308 | * - all other users take the lock (ie we can only | |
309 | * have _one_ other CPU that looks at or modifies | |
310 | * the list). | |
311 | */ | |
2055da97 | 312 | if (!list_empty_careful(&wq_entry->entry)) { |
9d9d676f | 313 | spin_lock_irqsave(&wq_head->lock, flags); |
2055da97 | 314 | list_del_init(&wq_entry->entry); |
9d9d676f | 315 | spin_unlock_irqrestore(&wq_head->lock, flags); |
1da177e4 LT |
316 | } |
317 | } | |
318 | EXPORT_SYMBOL(finish_wait); | |
319 | ||
50816c48 | 320 | int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
1da177e4 | 321 | { |
50816c48 | 322 | int ret = default_wake_function(wq_entry, mode, sync, key); |
1da177e4 LT |
323 | |
324 | if (ret) | |
2055da97 | 325 | list_del_init(&wq_entry->entry); |
1da177e4 LT |
326 | return ret; |
327 | } | |
328 | EXPORT_SYMBOL(autoremove_wake_function); | |
329 | ||
cb6538e7 PZ |
330 | static inline bool is_kthread_should_stop(void) |
331 | { | |
332 | return (current->flags & PF_KTHREAD) && kthread_should_stop(); | |
333 | } | |
61ada528 PZ |
334 | |
335 | /* | |
336 | * DEFINE_WAIT_FUNC(wait, woken_wake_func); | |
337 | * | |
9d9d676f | 338 | * add_wait_queue(&wq_head, &wait); |
61ada528 PZ |
339 | * for (;;) { |
340 | * if (condition) | |
341 | * break; | |
342 | * | |
343 | * p->state = mode; condition = true; | |
344 | * smp_mb(); // A smp_wmb(); // C | |
50816c48 | 345 | * if (!wq_entry->flags & WQ_FLAG_WOKEN) wq_entry->flags |= WQ_FLAG_WOKEN; |
61ada528 PZ |
346 | * schedule() try_to_wake_up(); |
347 | * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~ | |
50816c48 | 348 | * wq_entry->flags &= ~WQ_FLAG_WOKEN; condition = true; |
61ada528 | 349 | * smp_mb() // B smp_wmb(); // C |
50816c48 | 350 | * wq_entry->flags |= WQ_FLAG_WOKEN; |
61ada528 | 351 | * } |
9d9d676f | 352 | * remove_wait_queue(&wq_head, &wait); |
61ada528 PZ |
353 | * |
354 | */ | |
50816c48 | 355 | long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) |
61ada528 PZ |
356 | { |
357 | set_current_state(mode); /* A */ | |
358 | /* | |
359 | * The above implies an smp_mb(), which matches with the smp_wmb() from | |
360 | * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must | |
361 | * also observe all state before the wakeup. | |
362 | */ | |
50816c48 | 363 | if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) |
61ada528 PZ |
364 | timeout = schedule_timeout(timeout); |
365 | __set_current_state(TASK_RUNNING); | |
366 | ||
367 | /* | |
368 | * The below implies an smp_mb(), it too pairs with the smp_wmb() from | |
369 | * woken_wake_function() such that we must either observe the wait | |
370 | * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss | |
371 | * an event. | |
372 | */ | |
50816c48 | 373 | smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */ |
61ada528 PZ |
374 | |
375 | return timeout; | |
376 | } | |
377 | EXPORT_SYMBOL(wait_woken); | |
378 | ||
50816c48 | 379 | int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
61ada528 PZ |
380 | { |
381 | /* | |
382 | * Although this function is called under waitqueue lock, LOCK | |
383 | * doesn't imply write barrier and the users expects write | |
384 | * barrier semantics on wakeup functions. The following | |
385 | * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up() | |
b92b8b35 | 386 | * and is paired with smp_store_mb() in wait_woken(). |
61ada528 PZ |
387 | */ |
388 | smp_wmb(); /* C */ | |
50816c48 | 389 | wq_entry->flags |= WQ_FLAG_WOKEN; |
61ada528 | 390 | |
50816c48 | 391 | return default_wake_function(wq_entry, mode, sync, key); |
61ada528 PZ |
392 | } |
393 | EXPORT_SYMBOL(woken_wake_function); |