projects/linux·blob v4.13 · refs

393 lines · 11.8 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/signal.h>
9#include <linux/sched/debug.h>
10#include <linux/mm.h>
11#include <linux/wait.h>
12#include <linux/hash.h>
13#include <linux/kthread.h>
14
15void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
16{
17 spin_lock_init(&wq_head->lock);
18 lockdep_set_class_and_name(&wq_head->lock, key, name);
19 INIT_LIST_HEAD(&wq_head->head);
20}
21
22EXPORT_SYMBOL(__init_waitqueue_head);
23
24void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
25{
26 unsigned long flags;
27
28 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
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);
32}
33EXPORT_SYMBOL(add_wait_queue);
34
35void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
36{
37 unsigned long flags;
38
39 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
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);
43}
44EXPORT_SYMBOL(add_wait_queue_exclusive);
45
46void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
47{
48 unsigned long flags;
49
50 spin_lock_irqsave(&wq_head->lock, flags);
51 __remove_wait_queue(wq_head, wq_entry);
52 spin_unlock_irqrestore(&wq_head->lock, flags);
53}
54EXPORT_SYMBOL(remove_wait_queue);
55
56
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 */
66static void __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
67 int nr_exclusive, int wake_flags, void *key)
68{
69 wait_queue_entry_t *curr, *next;
70
71 list_for_each_entry_safe(curr, next, &wq_head->head, entry) {
72 unsigned flags = curr->flags;
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)
77 break;
78 }
79}
80
81/**
82 * __wake_up - wake up threads blocked on a waitqueue.
83 * @wq_head: the waitqueue
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 */
91void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
92 int nr_exclusive, void *key)
93{
94 unsigned long flags;
95
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);
99}
100EXPORT_SYMBOL(__wake_up);
101
102/*
103 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
104 */
105void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
106{
107 __wake_up_common(wq_head, mode, nr, 0, NULL);
108}
109EXPORT_SYMBOL_GPL(__wake_up_locked);
110
111void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
112{
113 __wake_up_common(wq_head, mode, 1, 0, key);
114}
115EXPORT_SYMBOL_GPL(__wake_up_locked_key);
116
117/**
118 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
119 * @wq_head: the waitqueue
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 */
134void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
135 int nr_exclusive, void *key)
136{
137 unsigned long flags;
138 int wake_flags = 1; /* XXX WF_SYNC */
139
140 if (unlikely(!wq_head))
141 return;
142
143 if (unlikely(nr_exclusive != 1))
144 wake_flags = 0;
145
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);
149}
150EXPORT_SYMBOL_GPL(__wake_up_sync_key);
151
152/*
153 * __wake_up_sync - see __wake_up_sync_key()
154 */
155void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
156{
157 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
158}
159EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
160
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
171 * loads to move into the critical region).
172 */
173void
174prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
175{
176 unsigned long flags;
177
178 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
179 spin_lock_irqsave(&wq_head->lock, flags);
180 if (list_empty(&wq_entry->entry))
181 __add_wait_queue(wq_head, wq_entry);
182 set_current_state(state);
183 spin_unlock_irqrestore(&wq_head->lock, flags);
184}
185EXPORT_SYMBOL(prepare_to_wait);
186
187void
188prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
189{
190 unsigned long flags;
191
192 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
193 spin_lock_irqsave(&wq_head->lock, flags);
194 if (list_empty(&wq_entry->entry))
195 __add_wait_queue_entry_tail(wq_head, wq_entry);
196 set_current_state(state);
197 spin_unlock_irqrestore(&wq_head->lock, flags);
198}
199EXPORT_SYMBOL(prepare_to_wait_exclusive);
200
201void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
202{
203 wq_entry->flags = flags;
204 wq_entry->private = current;
205 wq_entry->func = autoremove_wake_function;
206 INIT_LIST_HEAD(&wq_entry->entry);
207}
208EXPORT_SYMBOL(init_wait_entry);
209
210long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
211{
212 unsigned long flags;
213 long ret = 0;
214
215 spin_lock_irqsave(&wq_head->lock, flags);
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
223 * wakeup locks/unlocks the same wq_head->lock.
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 */
229 list_del_init(&wq_entry->entry);
230 ret = -ERESTARTSYS;
231 } else {
232 if (list_empty(&wq_entry->entry)) {
233 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
234 __add_wait_queue_entry_tail(wq_head, wq_entry);
235 else
236 __add_wait_queue(wq_head, wq_entry);
237 }
238 set_current_state(state);
239 }
240 spin_unlock_irqrestore(&wq_head->lock, flags);
241
242 return ret;
243}
244EXPORT_SYMBOL(prepare_to_wait_event);
245
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 */
253int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
254{
255 if (likely(list_empty(&wait->entry)))
256 __add_wait_queue_entry_tail(wq, wait);
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}
267EXPORT_SYMBOL(do_wait_intr);
268
269int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
270{
271 if (likely(list_empty(&wait->entry)))
272 __add_wait_queue_entry_tail(wq, wait);
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}
283EXPORT_SYMBOL(do_wait_intr_irq);
284
285/**
286 * finish_wait - clean up after waiting in a queue
287 * @wq_head: waitqueue waited on
288 * @wq_entry: wait descriptor
289 *
290 * Sets current thread back to running state and removes
291 * the wait descriptor from the given waitqueue if still
292 * queued.
293 */
294void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
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 */
312 if (!list_empty_careful(&wq_entry->entry)) {
313 spin_lock_irqsave(&wq_head->lock, flags);
314 list_del_init(&wq_entry->entry);
315 spin_unlock_irqrestore(&wq_head->lock, flags);
316 }
317}
318EXPORT_SYMBOL(finish_wait);
319
320int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
321{
322 int ret = default_wake_function(wq_entry, mode, sync, key);
323
324 if (ret)
325 list_del_init(&wq_entry->entry);
326 return ret;
327}
328EXPORT_SYMBOL(autoremove_wake_function);
329
330static inline bool is_kthread_should_stop(void)
331{
332 return (current->flags & PF_KTHREAD) && kthread_should_stop();
333}
334
335/*
336 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
337 *
338 * add_wait_queue(&wq_head, &wait);
339 * for (;;) {
340 * if (condition)
341 * break;
342 *
343 * p->state = mode; condition = true;
344 * smp_mb(); // A smp_wmb(); // C
345 * if (!wq_entry->flags & WQ_FLAG_WOKEN) wq_entry->flags |= WQ_FLAG_WOKEN;
346 * schedule() try_to_wake_up();
347 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
348 * wq_entry->flags &= ~WQ_FLAG_WOKEN; condition = true;
349 * smp_mb() // B smp_wmb(); // C
350 * wq_entry->flags |= WQ_FLAG_WOKEN;
351 * }
352 * remove_wait_queue(&wq_head, &wait);
353 *
354 */
355long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
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 */
363 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
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 */
373 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
374
375 return timeout;
376}
377EXPORT_SYMBOL(wait_woken);
378
379int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
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()
386 * and is paired with smp_store_mb() in wait_woken().
387 */
388 smp_wmb(); /* C */
389 wq_entry->flags |= WQ_FLAG_WOKEN;
390
391 return default_wake_function(wq_entry, mode, sync, key);
392}
393EXPORT_SYMBOL(woken_wake_function);