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