1 // SPDX-License-Identifier: GPL-2.0-only
6  * This file implements counting semaphores.
7  * A counting semaphore may be acquired 'n' times before sleeping.
8  * See mutex.c for single-acquisition sleeping locks which enforce
18  * parts of the kernel expect to be able to use down() on a semaphore in
20  * irqsave variants for down(), down_interruptible() and down_killable()
23  * The ->count variable represents how many more tasks can acquire this
48 	WRITE_ONCE((sem)->last_holder, (unsigned long)current);  in hung_task_sem_set_holder()
53 	if (READ_ONCE((sem)->last_holder) == (unsigned long)current)  in hung_task_sem_clear_if_holder()
54 		WRITE_ONCE((sem)->last_holder, 0UL);  in hung_task_sem_clear_if_holder()
59 	return READ_ONCE(sem->last_holder);  in sem_last_holder()
76 	sem->count--;  in __sem_acquire()
81  * down - acquire the semaphore
91 void __sched down(struct semaphore *sem)  in down()  function
96 	raw_spin_lock_irqsave(&sem->lock, flags);  in down()
97 	if (likely(sem->count > 0))  in down()
101 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in down()
103 EXPORT_SYMBOL(down);
106  * down_interruptible - acquire the semaphore unless interrupted
111  * If the sleep is interrupted by a signal, this function will return -EINTR.
120 	raw_spin_lock_irqsave(&sem->lock, flags);  in down_interruptible()
121 	if (likely(sem->count > 0))  in down_interruptible()
125 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in down_interruptible()
132  * down_killable - acquire the semaphore unless killed
138  * -EINTR.  If the semaphore is successfully acquired, this function returns
147 	raw_spin_lock_irqsave(&sem->lock, flags);  in down_killable()
148 	if (likely(sem->count > 0))  in down_killable()
152 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in down_killable()
159  * down_trylock - try to acquire the semaphore, without waiting
176 	raw_spin_lock_irqsave(&sem->lock, flags);  in down_trylock()
177 	count = sem->count - 1;  in down_trylock()
180 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in down_trylock()
187  * down_timeout - acquire the semaphore within a specified time
194  * this function returns -ETIME.  It returns 0 if the semaphore was acquired.
202 	raw_spin_lock_irqsave(&sem->lock, flags);  in down_timeout()
203 	if (likely(sem->count > 0))  in down_timeout()
207 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in down_timeout()
214  * up - release the semaphore
218  * context and even by tasks which have never called down().
225 	raw_spin_lock_irqsave(&sem->lock, flags);  in up()
229 	if (likely(list_empty(&sem->wait_list)))  in up()
230 		sem->count++;  in up()
233 	raw_spin_unlock_irqrestore(&sem->lock, flags);  in up()
257 	list_add_tail(&waiter.list, &sem->wait_list);  in ___down_common()
267 		raw_spin_unlock_irq(&sem->lock);  in ___down_common()
269 		raw_spin_lock_irq(&sem->lock);  in ___down_common()
278 	return -ETIME;  in ___down_common()
282 	return -EINTR;  in ___down_common()
324 	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,  in __up()
326 	list_del(&waiter->list);  in __up()
327 	waiter->up = true;  in __up()
328 	wake_q_add(wake_q, waiter->task);  in __up()