projects/linux·blob v2.6.26 · refs

264 lines · 7.2 KiB

1/*
2 * Copyright (c) 2008 Intel Corporation
3 * Author: Matthew Wilcox <[email protected]>
4 *
5 * Distributed under the terms of the GNU GPL, version 2
6 *
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.
11 */
12
13/*
14 * Some notes on the implementation:
15 *
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()
22 * too.
23 *
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.
26 */
27
28#include <linux/compiler.h>
29#include <linux/kernel.h>
30#include <linux/module.h>
31#include <linux/sched.h>
32#include <linux/semaphore.h>
33#include <linux/spinlock.h>
34
35static noinline void __down(struct semaphore *sem);
36static noinline int __down_interruptible(struct semaphore *sem);
37static noinline int __down_killable(struct semaphore *sem);
38static noinline int __down_timeout(struct semaphore *sem, long jiffies);
39static noinline void __up(struct semaphore *sem);
40
41/**
42 * down - acquire the semaphore
43 * @sem: the semaphore to be acquired
44 *
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.
48 *
49 * Use of this function is deprecated, please use down_interruptible() or
50 * down_killable() instead.
51 */
52void down(struct semaphore *sem)
53{
54 unsigned long flags;
55
56 spin_lock_irqsave(&sem->lock, flags);
57 if (likely(sem->count > 0))
58 sem->count--;
59 else
60 __down(sem);
61 spin_unlock_irqrestore(&sem->lock, flags);
62}
63EXPORT_SYMBOL(down);
64
65/**
66 * down_interruptible - acquire the semaphore unless interrupted
67 * @sem: the semaphore to be acquired
68 *
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.
73 */
74int down_interruptible(struct semaphore *sem)
75{
76 unsigned long flags;
77 int result = 0;
78
79 spin_lock_irqsave(&sem->lock, flags);
80 if (likely(sem->count > 0))
81 sem->count--;
82 else
83 result = __down_interruptible(sem);
84 spin_unlock_irqrestore(&sem->lock, flags);
85
86 return result;
87}
88EXPORT_SYMBOL(down_interruptible);
89
90/**
91 * down_killable - acquire the semaphore unless killed
92 * @sem: the semaphore to be acquired
93 *
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
98 * 0.
99 */
100int down_killable(struct semaphore *sem)
101{
102 unsigned long flags;
103 int result = 0;
104
105 spin_lock_irqsave(&sem->lock, flags);
106 if (likely(sem->count > 0))
107 sem->count--;
108 else
109 result = __down_killable(sem);
110 spin_unlock_irqrestore(&sem->lock, flags);
111
112 return result;
113}
114EXPORT_SYMBOL(down_killable);
115
116/**
117 * down_trylock - try to acquire the semaphore, without waiting
118 * @sem: the semaphore to be acquired
119 *
120 * Try to acquire the semaphore atomically. Returns 0 if the mutex has
121 * been acquired successfully or 1 if it it cannot be acquired.
122 *
123 * NOTE: This return value is inverted from both spin_trylock and
124 * mutex_trylock! Be careful about this when converting code.
125 *
126 * Unlike mutex_trylock, this function can be used from interrupt context,
127 * and the semaphore can be released by any task or interrupt.
128 */
129int down_trylock(struct semaphore *sem)
130{
131 unsigned long flags;
132 int count;
133
134 spin_lock_irqsave(&sem->lock, flags);
135 count = sem->count - 1;
136 if (likely(count >= 0))
137 sem->count = count;
138 spin_unlock_irqrestore(&sem->lock, flags);
139
140 return (count < 0);
141}
142EXPORT_SYMBOL(down_trylock);
143
144/**
145 * down_timeout - acquire the semaphore within a specified time
146 * @sem: the semaphore to be acquired
147 * @jiffies: how long to wait before failing
148 *
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.
153 */
154int down_timeout(struct semaphore *sem, long jiffies)
155{
156 unsigned long flags;
157 int result = 0;
158
159 spin_lock_irqsave(&sem->lock, flags);
160 if (likely(sem->count > 0))
161 sem->count--;
162 else
163 result = __down_timeout(sem, jiffies);
164 spin_unlock_irqrestore(&sem->lock, flags);
165
166 return result;
167}
168EXPORT_SYMBOL(down_timeout);
169
170/**
171 * up - release the semaphore
172 * @sem: the semaphore to release
173 *
174 * Release the semaphore. Unlike mutexes, up() may be called from any
175 * context and even by tasks which have never called down().
176 */
177void up(struct semaphore *sem)
178{
179 unsigned long flags;
180
181 spin_lock_irqsave(&sem->lock, flags);
182 if (likely(list_empty(&sem->wait_list)))
183 sem->count++;
184 else
185 __up(sem);
186 spin_unlock_irqrestore(&sem->lock, flags);
187}
188EXPORT_SYMBOL(up);
189
190/* Functions for the contended case */
191
192struct semaphore_waiter {
193 struct list_head list;
194 struct task_struct *task;
195 int up;
196};
197
198/*
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.
202 */
203static inline int __sched __down_common(struct semaphore *sem, long state,
204 long timeout)
205{
206 struct task_struct *task = current;
207 struct semaphore_waiter waiter;
208
209 list_add_tail(&waiter.list, &sem->wait_list);
210 waiter.task = task;
211 waiter.up = 0;
212
213 for (;;) {
214 if (state == TASK_INTERRUPTIBLE && signal_pending(task))
215 goto interrupted;
216 if (state == TASK_KILLABLE && fatal_signal_pending(task))
217 goto interrupted;
218 if (timeout <= 0)
219 goto timed_out;
220 __set_task_state(task, state);
221 spin_unlock_irq(&sem->lock);
222 timeout = schedule_timeout(timeout);
223 spin_lock_irq(&sem->lock);
224 if (waiter.up)
225 return 0;
226 }
227
228 timed_out:
229 list_del(&waiter.list);
230 return -ETIME;
231
232 interrupted:
233 list_del(&waiter.list);
234 return -EINTR;
235}
236
237static noinline void __sched __down(struct semaphore *sem)
238{
239 __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
240}
241
242static noinline int __sched __down_interruptible(struct semaphore *sem)
243{
244 return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
245}
246
247static noinline int __sched __down_killable(struct semaphore *sem)
248{
249 return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
250}
251
252static noinline int __sched __down_timeout(struct semaphore *sem, long jiffies)
253{
254 return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
255}
256
257static noinline void __sched __up(struct semaphore *sem)
258{
259 struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
260 struct semaphore_waiter, list);
261 list_del(&waiter->list);
262 waiter->up = 1;
263 wake_up_process(waiter->task);
264}