1// SPDX-License-Identifier: GPL-2.0
2
3/*
4 * Generic wait-for-completion handler;
5 *
6 * It differs from semaphores in that their default case is the opposite,
7 * wait_for_completion default blocks whereas semaphore default non-block. The
8 * interface also makes it easy to 'complete' multiple waiting threads,
9 * something which isn't entirely natural for semaphores.
10 *
11 * But more importantly, the primitive documents the usage. Semaphores would
12 * typically be used for exclusion which gives rise to priority inversion.
13 * Waiting for completion is a typically sync point, but not an exclusion point.
14 */
15
16static void complete_with_flags(struct completion *x, int wake_flags)
17{
18 unsigned long flags;
19
20 raw_spin_lock_irqsave(&x->wait.lock, flags);
21
22 if (x->done != UINT_MAX)
23 x->done++;
24 swake_up_locked(q: &x->wait, wake_flags);
25 raw_spin_unlock_irqrestore(&x->wait.lock, flags);
26}
27
28void complete_on_current_cpu(struct completion *x)
29{
30 return complete_with_flags(x, WF_CURRENT_CPU);
31}
32
33/**
34 * complete: - signals a single thread waiting on this completion
35 * @x: holds the state of this particular completion
36 *
37 * This will wake up a single thread waiting on this completion. Threads will be
38 * awakened in the same order in which they were queued.
39 *
40 * See also complete_all(), wait_for_completion() and related routines.
41 *
42 * If this function wakes up a task, it executes a full memory barrier before
43 * accessing the task state.
44 */
45void complete(struct completion *x)
46{
47 complete_with_flags(x, wake_flags: 0);
48}
49EXPORT_SYMBOL(complete);
50
51/**
52 * complete_all: - signals all threads waiting on this completion
53 * @x: holds the state of this particular completion
54 *
55 * This will wake up all threads waiting on this particular completion event.
56 *
57 * If this function wakes up a task, it executes a full memory barrier before
58 * accessing the task state.
59 *
60 * Since complete_all() sets the completion of @x permanently to done
61 * to allow multiple waiters to finish, a call to reinit_completion()
62 * must be used on @x if @x is to be used again. The code must make
63 * sure that all waiters have woken and finished before reinitializing
64 * @x. Also note that the function completion_done() can not be used
65 * to know if there are still waiters after complete_all() has been called.
66 */
67void complete_all(struct completion *x)
68{
69 unsigned long flags;
70
71 lockdep_assert_RT_in_threaded_ctx();
72
73 raw_spin_lock_irqsave(&x->wait.lock, flags);
74 x->done = UINT_MAX;
75 swake_up_all_locked(q: &x->wait);
76 raw_spin_unlock_irqrestore(&x->wait.lock, flags);
77}
78EXPORT_SYMBOL(complete_all);
79
80static inline long __sched
81do_wait_for_common(struct completion *x,
82 long (*action)(long), long timeout, int state)
83{
84 if (!x->done) {
85 DECLARE_SWAITQUEUE(wait);
86
87 do {
88 if (signal_pending_state(state, current)) {
89 timeout = -ERESTARTSYS;
90 break;
91 }
92 __prepare_to_swait(q: &x->wait, wait: &wait);
93 __set_current_state(state);
94 raw_spin_unlock_irq(&x->wait.lock);
95 timeout = action(timeout);
96 raw_spin_lock_irq(&x->wait.lock);
97 } while (!x->done && timeout);
98 __finish_swait(q: &x->wait, wait: &wait);
99 if (!x->done)
100 return timeout;
101 }
102 if (x->done != UINT_MAX)
103 x->done--;
104 return timeout ?: 1;
105}
106
107static inline long __sched
108__wait_for_common(struct completion *x,
109 long (*action)(long), long timeout, int state)
110{
111 might_sleep();
112
113 complete_acquire(x);
114
115 raw_spin_lock_irq(&x->wait.lock);
116 timeout = do_wait_for_common(x, action, timeout, state);
117 raw_spin_unlock_irq(&x->wait.lock);
118
119 complete_release(x);
120
121 return timeout;
122}
123
124static long __sched
125wait_for_common(struct completion *x, long timeout, int state)
126{
127 return __wait_for_common(x, action: schedule_timeout, timeout, state);
128}
129
130static long __sched
131wait_for_common_io(struct completion *x, long timeout, int state)
132{
133 return __wait_for_common(x, action: io_schedule_timeout, timeout, state);
134}
135
136/**
137 * wait_for_completion: - waits for completion of a task
138 * @x: holds the state of this particular completion
139 *
140 * This waits to be signaled for completion of a specific task. It is NOT
141 * interruptible and there is no timeout.
142 *
143 * See also similar routines (i.e. wait_for_completion_timeout()) with timeout
144 * and interrupt capability. Also see complete().
145 */
146void __sched wait_for_completion(struct completion *x)
147{
148 wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
149}
150EXPORT_SYMBOL(wait_for_completion);
151
152/**
153 * wait_for_completion_timeout: - waits for completion of a task (w/timeout)
154 * @x: holds the state of this particular completion
155 * @timeout: timeout value in jiffies
156 *
157 * This waits for either a completion of a specific task to be signaled or for a
158 * specified timeout to expire. The timeout is in jiffies. It is not
159 * interruptible.
160 *
161 * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
162 * till timeout) if completed.
163 */
164unsigned long __sched
165wait_for_completion_timeout(struct completion *x, unsigned long timeout)
166{
167 return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
168}
169EXPORT_SYMBOL(wait_for_completion_timeout);
170
171/**
172 * wait_for_completion_io: - waits for completion of a task
173 * @x: holds the state of this particular completion
174 *
175 * This waits to be signaled for completion of a specific task. It is NOT
176 * interruptible and there is no timeout. The caller is accounted as waiting
177 * for IO (which traditionally means blkio only).
178 */
179void __sched wait_for_completion_io(struct completion *x)
180{
181 wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
182}
183EXPORT_SYMBOL(wait_for_completion_io);
184
185/**
186 * wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
187 * @x: holds the state of this particular completion
188 * @timeout: timeout value in jiffies
189 *
190 * This waits for either a completion of a specific task to be signaled or for a
191 * specified timeout to expire. The timeout is in jiffies. It is not
192 * interruptible. The caller is accounted as waiting for IO (which traditionally
193 * means blkio only).
194 *
195 * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
196 * till timeout) if completed.
197 */
198unsigned long __sched
199wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
200{
201 return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE);
202}
203EXPORT_SYMBOL(wait_for_completion_io_timeout);
204
205/**
206 * wait_for_completion_interruptible: - waits for completion of a task (w/intr)
207 * @x: holds the state of this particular completion
208 *
209 * This waits for completion of a specific task to be signaled. It is
210 * interruptible.
211 *
212 * Return: -ERESTARTSYS if interrupted, 0 if completed.
213 */
214int __sched wait_for_completion_interruptible(struct completion *x)
215{
216 long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
217
218 if (t == -ERESTARTSYS)
219 return t;
220 return 0;
221}
222EXPORT_SYMBOL(wait_for_completion_interruptible);
223
224/**
225 * wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
226 * @x: holds the state of this particular completion
227 * @timeout: timeout value in jiffies
228 *
229 * This waits for either a completion of a specific task to be signaled or for a
230 * specified timeout to expire. It is interruptible. The timeout is in jiffies.
231 *
232 * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
233 * or number of jiffies left till timeout) if completed.
234 */
235long __sched
236wait_for_completion_interruptible_timeout(struct completion *x,
237 unsigned long timeout)
238{
239 return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
240}
241EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);
242
243/**
244 * wait_for_completion_killable: - waits for completion of a task (killable)
245 * @x: holds the state of this particular completion
246 *
247 * This waits to be signaled for completion of a specific task. It can be
248 * interrupted by a kill signal.
249 *
250 * Return: -ERESTARTSYS if interrupted, 0 if completed.
251 */
252int __sched wait_for_completion_killable(struct completion *x)
253{
254 long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE);
255
256 if (t == -ERESTARTSYS)
257 return t;
258 return 0;
259}
260EXPORT_SYMBOL(wait_for_completion_killable);
261
262int __sched wait_for_completion_state(struct completion *x, unsigned int state)
263{
264 long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, state);
265
266 if (t == -ERESTARTSYS)
267 return t;
268 return 0;
269}
270EXPORT_SYMBOL(wait_for_completion_state);
271
272/**
273 * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
274 * @x: holds the state of this particular completion
275 * @timeout: timeout value in jiffies
276 *
277 * This waits for either a completion of a specific task to be
278 * signaled or for a specified timeout to expire. It can be
279 * interrupted by a kill signal. The timeout is in jiffies.
280 *
281 * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
282 * or number of jiffies left till timeout) if completed.
283 */
284long __sched
285wait_for_completion_killable_timeout(struct completion *x,
286 unsigned long timeout)
287{
288 return wait_for_common(x, timeout, TASK_KILLABLE);
289}
290EXPORT_SYMBOL(wait_for_completion_killable_timeout);
291
292/**
293 * try_wait_for_completion - try to decrement a completion without blocking
294 * @x: completion structure
295 *
296 * Return: 0 if a decrement cannot be done without blocking
297 * 1 if a decrement succeeded.
298 *
299 * If a completion is being used as a counting completion,
300 * attempt to decrement the counter without blocking. This
301 * enables us to avoid waiting if the resource the completion
302 * is protecting is not available.
303 */
304bool try_wait_for_completion(struct completion *x)
305{
306 unsigned long flags;
307 bool ret = true;
308
309 /*
310 * Since x->done will need to be locked only
311 * in the non-blocking case, we check x->done
312 * first without taking the lock so we can
313 * return early in the blocking case.
314 */
315 if (!READ_ONCE(x->done))
316 return false;
317
318 raw_spin_lock_irqsave(&x->wait.lock, flags);
319 if (!x->done)
320 ret = false;
321 else if (x->done != UINT_MAX)
322 x->done--;
323 raw_spin_unlock_irqrestore(&x->wait.lock, flags);
324 return ret;
325}
326EXPORT_SYMBOL(try_wait_for_completion);
327
328/**
329 * completion_done - Test to see if a completion has any waiters
330 * @x: completion structure
331 *
332 * Return: 0 if there are waiters (wait_for_completion() in progress)
333 * 1 if there are no waiters.
334 *
335 * Note, this will always return true if complete_all() was called on @X.
336 */
337bool completion_done(struct completion *x)
338{
339 unsigned long flags;
340
341 if (!READ_ONCE(x->done))
342 return false;
343
344 /*
345 * If ->done, we need to wait for complete() to release ->wait.lock
346 * otherwise we can end up freeing the completion before complete()
347 * is done referencing it.
348 */
349 raw_spin_lock_irqsave(&x->wait.lock, flags);
350 raw_spin_unlock_irqrestore(&x->wait.lock, flags);
351 return true;
352}
353EXPORT_SYMBOL(completion_done);
354

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source code of linux/kernel/sched/completion.c