1 // SPDX-License-Identifier: GPL-2.0-only
3 * Copyright (c) 2008 Intel Corporation
4 * Author: Matthew Wilcox <willy@linux.intel.com>
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
9 * rules which allow code to be debugged more easily.
13 * Some notes on the implementation:
15 * The spinlock controls access to the other members of the semaphore.
16 * down_trylock() and up() can be called from interrupt context, so we
17 * have to disable interrupts when taking the lock. It turns out various
18 * parts of the kernel expect to be able to use down() on a semaphore in
19 * interrupt context when they know it will succeed, so we have to use
20 * irqsave variants for down(), down_interruptible() and down_killable()
23 * The ->count variable represents how many more tasks can acquire this
24 * semaphore. If it's zero, there may be tasks waiting on the wait_list.
27 #include <linux/compiler.h>
28 #include <linux/kernel.h>
29 #include <linux/export.h>
30 #include <linux/sched.h>
31 #include <linux/sched/debug.h>
32 #include <linux/semaphore.h>
33 #include <linux/spinlock.h>
34 #include <linux/ftrace.h>
36 static noinline void __down(struct semaphore *sem);
37 static noinline int __down_interruptible(struct semaphore *sem);
38 static noinline int __down_killable(struct semaphore *sem);
39 static noinline int __down_timeout(struct semaphore *sem, long timeout);
40 static noinline void __up(struct semaphore *sem);
43 * down - acquire the semaphore
44 * @sem: the semaphore to be acquired
46 * Acquires the semaphore. If no more tasks are allowed to acquire the
47 * semaphore, calling this function will put the task to sleep until the
48 * semaphore is released.
50 * Use of this function is deprecated, please use down_interruptible() or
51 * down_killable() instead.
53 void down(struct semaphore *sem)
57 raw_spin_lock_irqsave(&sem->lock, flags);
58 if (likely(sem->count > 0))
62 raw_spin_unlock_irqrestore(&sem->lock, flags);
67 * down_interruptible - acquire the semaphore unless interrupted
68 * @sem: the semaphore to be acquired
70 * Attempts to acquire the semaphore. If no more tasks are allowed to
71 * acquire the semaphore, calling this function will put the task to sleep.
72 * If the sleep is interrupted by a signal, this function will return -EINTR.
73 * If the semaphore is successfully acquired, this function returns 0.
75 int down_interruptible(struct semaphore *sem)
80 raw_spin_lock_irqsave(&sem->lock, flags);
81 if (likely(sem->count > 0))
84 result = __down_interruptible(sem);
85 raw_spin_unlock_irqrestore(&sem->lock, flags);
89 EXPORT_SYMBOL(down_interruptible);
92 * down_killable - acquire the semaphore unless killed
93 * @sem: the semaphore to be acquired
95 * Attempts to acquire the semaphore. If no more tasks are allowed to
96 * acquire the semaphore, calling this function will put the task to sleep.
97 * If the sleep is interrupted by a fatal signal, this function will return
98 * -EINTR. If the semaphore is successfully acquired, this function returns
101 int down_killable(struct semaphore *sem)
106 raw_spin_lock_irqsave(&sem->lock, flags);
107 if (likely(sem->count > 0))
110 result = __down_killable(sem);
111 raw_spin_unlock_irqrestore(&sem->lock, flags);
115 EXPORT_SYMBOL(down_killable);
118 * down_trylock - try to acquire the semaphore, without waiting
119 * @sem: the semaphore to be acquired
121 * Try to acquire the semaphore atomically. Returns 0 if the semaphore has
122 * been acquired successfully or 1 if it cannot be acquired.
124 * NOTE: This return value is inverted from both spin_trylock and
125 * mutex_trylock! Be careful about this when converting code.
127 * Unlike mutex_trylock, this function can be used from interrupt context,
128 * and the semaphore can be released by any task or interrupt.
130 int down_trylock(struct semaphore *sem)
135 raw_spin_lock_irqsave(&sem->lock, flags);
136 count = sem->count - 1;
137 if (likely(count >= 0))
139 raw_spin_unlock_irqrestore(&sem->lock, flags);
143 EXPORT_SYMBOL(down_trylock);
146 * down_timeout - acquire the semaphore within a specified time
147 * @sem: the semaphore to be acquired
148 * @timeout: how long to wait before failing
150 * Attempts to acquire the semaphore. If no more tasks are allowed to
151 * acquire the semaphore, calling this function will put the task to sleep.
152 * If the semaphore is not released within the specified number of jiffies,
153 * this function returns -ETIME. It returns 0 if the semaphore was acquired.
155 int down_timeout(struct semaphore *sem, long timeout)
160 raw_spin_lock_irqsave(&sem->lock, flags);
161 if (likely(sem->count > 0))
164 result = __down_timeout(sem, timeout);
165 raw_spin_unlock_irqrestore(&sem->lock, flags);
169 EXPORT_SYMBOL(down_timeout);
172 * up - release the semaphore
173 * @sem: the semaphore to release
175 * Release the semaphore. Unlike mutexes, up() may be called from any
176 * context and even by tasks which have never called down().
178 void up(struct semaphore *sem)
182 raw_spin_lock_irqsave(&sem->lock, flags);
183 if (likely(list_empty(&sem->wait_list)))
187 raw_spin_unlock_irqrestore(&sem->lock, flags);
191 /* Functions for the contended case */
193 struct semaphore_waiter {
194 struct list_head list;
195 struct task_struct *task;
200 * Because this function is inlined, the 'state' parameter will be
201 * constant, and thus optimised away by the compiler. Likewise the
202 * 'timeout' parameter for the cases without timeouts.
204 static inline int __sched __down_common(struct semaphore *sem, long state,
207 struct semaphore_waiter waiter;
209 list_add_tail(&waiter.list, &sem->wait_list);
210 waiter.task = current;
214 if (signal_pending_state(state, current))
216 if (unlikely(timeout <= 0))
218 __set_current_state(state);
219 raw_spin_unlock_irq(&sem->lock);
220 timeout = schedule_timeout(timeout);
221 raw_spin_lock_irq(&sem->lock);
227 list_del(&waiter.list);
231 list_del(&waiter.list);
235 static noinline void __sched __down(struct semaphore *sem)
237 __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
240 static noinline int __sched __down_interruptible(struct semaphore *sem)
242 return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
245 static noinline int __sched __down_killable(struct semaphore *sem)
247 return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
250 static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
252 return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
255 static noinline void __sched __up(struct semaphore *sem)
257 struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
258 struct semaphore_waiter, list);
259 list_del(&waiter->list);
261 wake_up_process(waiter->task);