2 * Copyright (c) 2008 Intel Corporation
3 * Author: Matthew Wilcox <willy@linux.intel.com>
5 * Distributed under the terms of the GNU GPL, version 2
7 * This file implements counting semaphores.
8 * A counting semaphore may be acquired 'n' times before sleeping.
9 * See mutex.c for single-acquisition sleeping locks which enforce
10 * rules which allow code to be debugged more easily.
14 * Some notes on the implementation:
16 * The spinlock controls access to the other members of the semaphore.
17 * down_trylock() and up() can be called from interrupt context, so we
18 * have to disable interrupts when taking the lock. It turns out various
19 * parts of the kernel expect to be able to use down() on a semaphore in
20 * interrupt context when they know it will succeed, so we have to use
21 * irqsave variants for down(), down_interruptible() and down_killable()
24 * The ->count variable represents how many more tasks can acquire this
25 * semaphore. If it's zero, there may be tasks waiting on the wait_list.
28 #include <linux/compiler.h>
29 #include <linux/kernel.h>
30 #include <linux/export.h>
31 #include <linux/sched.h>
32 #include <linux/semaphore.h>
33 #include <linux/spinlock.h>
35 static noinline void __down(struct semaphore *sem);
36 static noinline int __down_interruptible(struct semaphore *sem);
37 static noinline int __down_killable(struct semaphore *sem);
38 static noinline int __down_timeout(struct semaphore *sem, long timeout);
39 static noinline void __up(struct semaphore *sem);
42 * down - acquire the semaphore
43 * @sem: the semaphore to be acquired
45 * Acquires the semaphore. If no more tasks are allowed to acquire the
46 * semaphore, calling this function will put the task to sleep until the
47 * semaphore is released.
49 * Use of this function is deprecated, please use down_interruptible() or
50 * down_killable() instead.
52 void down(struct semaphore *sem)
56 raw_spin_lock_irqsave(&sem->lock, flags);
57 if (likely(sem->count > 0))
61 raw_spin_unlock_irqrestore(&sem->lock, flags);
66 * down_interruptible - acquire the semaphore unless interrupted
67 * @sem: the semaphore to be acquired
69 * Attempts to acquire the semaphore. If no more tasks are allowed to
70 * acquire the semaphore, calling this function will put the task to sleep.
71 * If the sleep is interrupted by a signal, this function will return -EINTR.
72 * If the semaphore is successfully acquired, this function returns 0.
74 int down_interruptible(struct semaphore *sem)
79 raw_spin_lock_irqsave(&sem->lock, flags);
80 if (likely(sem->count > 0))
83 result = __down_interruptible(sem);
84 raw_spin_unlock_irqrestore(&sem->lock, flags);
88 EXPORT_SYMBOL(down_interruptible);
91 * down_killable - acquire the semaphore unless killed
92 * @sem: the semaphore to be acquired
94 * Attempts to acquire the semaphore. If no more tasks are allowed to
95 * acquire the semaphore, calling this function will put the task to sleep.
96 * If the sleep is interrupted by a fatal signal, this function will return
97 * -EINTR. If the semaphore is successfully acquired, this function returns
100 int down_killable(struct semaphore *sem)
105 raw_spin_lock_irqsave(&sem->lock, flags);
106 if (likely(sem->count > 0))
109 result = __down_killable(sem);
110 raw_spin_unlock_irqrestore(&sem->lock, flags);
114 EXPORT_SYMBOL(down_killable);
117 * down_trylock - try to acquire the semaphore, without waiting
118 * @sem: the semaphore to be acquired
120 * Try to acquire the semaphore atomically. Returns 0 if the semaphore has
121 * been acquired successfully or 1 if it it cannot be acquired.
123 * NOTE: This return value is inverted from both spin_trylock and
124 * mutex_trylock! Be careful about this when converting code.
126 * Unlike mutex_trylock, this function can be used from interrupt context,
127 * and the semaphore can be released by any task or interrupt.
129 int down_trylock(struct semaphore *sem)
134 raw_spin_lock_irqsave(&sem->lock, flags);
135 count = sem->count - 1;
136 if (likely(count >= 0))
138 raw_spin_unlock_irqrestore(&sem->lock, flags);
142 EXPORT_SYMBOL(down_trylock);
145 * down_timeout - acquire the semaphore within a specified time
146 * @sem: the semaphore to be acquired
147 * @timeout: how long to wait before failing
149 * Attempts to acquire the semaphore. If no more tasks are allowed to
150 * acquire the semaphore, calling this function will put the task to sleep.
151 * If the semaphore is not released within the specified number of jiffies,
152 * this function returns -ETIME. It returns 0 if the semaphore was acquired.
154 int down_timeout(struct semaphore *sem, long timeout)
159 raw_spin_lock_irqsave(&sem->lock, flags);
160 if (likely(sem->count > 0))
163 result = __down_timeout(sem, timeout);
164 raw_spin_unlock_irqrestore(&sem->lock, flags);
168 EXPORT_SYMBOL(down_timeout);
171 * up - release the semaphore
172 * @sem: the semaphore to release
174 * Release the semaphore. Unlike mutexes, up() may be called from any
175 * context and even by tasks which have never called down().
177 void up(struct semaphore *sem)
181 raw_spin_lock_irqsave(&sem->lock, flags);
182 if (likely(list_empty(&sem->wait_list)))
186 raw_spin_unlock_irqrestore(&sem->lock, flags);
190 /* Functions for the contended case */
192 struct semaphore_waiter {
193 struct list_head list;
194 struct task_struct *task;
199 * Because this function is inlined, the 'state' parameter will be
200 * constant, and thus optimised away by the compiler. Likewise the
201 * 'timeout' parameter for the cases without timeouts.
203 static inline int __sched __down_common(struct semaphore *sem, long state,
206 struct task_struct *task = current;
207 struct semaphore_waiter waiter;
209 list_add_tail(&waiter.list, &sem->wait_list);
214 if (unlikely(timeout <= 0))
216 __set_task_state(task, state);
217 raw_spin_unlock_irq(&sem->lock);
218 timeout = schedule_timeout(timeout);
219 raw_spin_lock_irq(&sem->lock);
225 list_del(&waiter.list);
229 static noinline void __sched __down(struct semaphore *sem)
231 __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
234 static noinline int __sched __down_interruptible(struct semaphore *sem)
236 return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
239 static noinline int __sched __down_killable(struct semaphore *sem)
241 return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
244 static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
246 return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
249 static noinline void __sched __up(struct semaphore *sem)
251 struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
252 struct semaphore_waiter, list);
253 list_del(&waiter->list);
255 wake_up_process(waiter->task);