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git.proxmox.com Git - mirror_ubuntu-artful-kernel.git/blob - kernel/semaphore.c
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/module.h>
31 #include <linux/sched.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 jiffies
);
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 ftrace_special(sem
->count
, 0, __LINE__
);
58 spin_lock_irqsave(&sem
->lock
, flags
);
59 if (likely(sem
->count
> 0))
63 spin_unlock_irqrestore(&sem
->lock
, flags
);
68 * down_interruptible - acquire the semaphore unless interrupted
69 * @sem: the semaphore to be acquired
71 * Attempts to acquire the semaphore. If no more tasks are allowed to
72 * acquire the semaphore, calling this function will put the task to sleep.
73 * If the sleep is interrupted by a signal, this function will return -EINTR.
74 * If the semaphore is successfully acquired, this function returns 0.
76 int down_interruptible(struct semaphore
*sem
)
81 spin_lock_irqsave(&sem
->lock
, flags
);
82 if (likely(sem
->count
> 0))
85 result
= __down_interruptible(sem
);
86 spin_unlock_irqrestore(&sem
->lock
, flags
);
90 EXPORT_SYMBOL(down_interruptible
);
93 * down_killable - acquire the semaphore unless killed
94 * @sem: the semaphore to be acquired
96 * Attempts to acquire the semaphore. If no more tasks are allowed to
97 * acquire the semaphore, calling this function will put the task to sleep.
98 * If the sleep is interrupted by a fatal signal, this function will return
99 * -EINTR. If the semaphore is successfully acquired, this function returns
102 int down_killable(struct semaphore
*sem
)
107 spin_lock_irqsave(&sem
->lock
, flags
);
108 if (likely(sem
->count
> 0))
111 result
= __down_killable(sem
);
112 spin_unlock_irqrestore(&sem
->lock
, flags
);
116 EXPORT_SYMBOL(down_killable
);
119 * down_trylock - try to acquire the semaphore, without waiting
120 * @sem: the semaphore to be acquired
122 * Try to acquire the semaphore atomically. Returns 0 if the mutex has
123 * been acquired successfully or 1 if it it cannot be acquired.
125 * NOTE: This return value is inverted from both spin_trylock and
126 * mutex_trylock! Be careful about this when converting code.
128 * Unlike mutex_trylock, this function can be used from interrupt context,
129 * and the semaphore can be released by any task or interrupt.
131 int down_trylock(struct semaphore
*sem
)
136 spin_lock_irqsave(&sem
->lock
, flags
);
137 count
= sem
->count
- 1;
138 if (likely(count
>= 0))
140 spin_unlock_irqrestore(&sem
->lock
, flags
);
144 EXPORT_SYMBOL(down_trylock
);
147 * down_timeout - acquire the semaphore within a specified time
148 * @sem: the semaphore to be acquired
149 * @jiffies: how long to wait before failing
151 * Attempts to acquire the semaphore. If no more tasks are allowed to
152 * acquire the semaphore, calling this function will put the task to sleep.
153 * If the semaphore is not released within the specified number of jiffies,
154 * this function returns -ETIME. It returns 0 if the semaphore was acquired.
156 int down_timeout(struct semaphore
*sem
, long jiffies
)
161 spin_lock_irqsave(&sem
->lock
, flags
);
162 if (likely(sem
->count
> 0))
165 result
= __down_timeout(sem
, jiffies
);
166 spin_unlock_irqrestore(&sem
->lock
, flags
);
170 EXPORT_SYMBOL(down_timeout
);
173 * up - release the semaphore
174 * @sem: the semaphore to release
176 * Release the semaphore. Unlike mutexes, up() may be called from any
177 * context and even by tasks which have never called down().
179 void up(struct semaphore
*sem
)
183 spin_lock_irqsave(&sem
->lock
, flags
);
184 if (likely(list_empty(&sem
->wait_list
)))
188 spin_unlock_irqrestore(&sem
->lock
, flags
);
192 /* Functions for the contended case */
194 struct semaphore_waiter
{
195 struct list_head list
;
196 struct task_struct
*task
;
201 * Because this function is inlined, the 'state' parameter will be
202 * constant, and thus optimised away by the compiler. Likewise the
203 * 'timeout' parameter for the cases without timeouts.
205 static inline int __sched
__down_common(struct semaphore
*sem
, long state
,
208 struct task_struct
*task
= current
;
209 struct semaphore_waiter waiter
;
211 list_add_tail(&waiter
.list
, &sem
->wait_list
);
216 if (state
== TASK_INTERRUPTIBLE
&& signal_pending(task
))
218 if (state
== TASK_KILLABLE
&& fatal_signal_pending(task
))
222 __set_task_state(task
, state
);
223 spin_unlock_irq(&sem
->lock
);
224 timeout
= schedule_timeout(timeout
);
225 spin_lock_irq(&sem
->lock
);
231 list_del(&waiter
.list
);
235 list_del(&waiter
.list
);
239 static noinline
void __sched
__down(struct semaphore
*sem
)
241 __down_common(sem
, TASK_UNINTERRUPTIBLE
, MAX_SCHEDULE_TIMEOUT
);
244 static noinline
int __sched
__down_interruptible(struct semaphore
*sem
)
246 return __down_common(sem
, TASK_INTERRUPTIBLE
, MAX_SCHEDULE_TIMEOUT
);
249 static noinline
int __sched
__down_killable(struct semaphore
*sem
)
251 return __down_common(sem
, TASK_KILLABLE
, MAX_SCHEDULE_TIMEOUT
);
254 static noinline
int __sched
__down_timeout(struct semaphore
*sem
, long jiffies
)
256 return __down_common(sem
, TASK_UNINTERRUPTIBLE
, jiffies
);
259 static noinline
void __sched
__up(struct semaphore
*sem
)
261 struct semaphore_waiter
*waiter
= list_first_entry(&sem
->wait_list
,
262 struct semaphore_waiter
, list
);
263 list_del(&waiter
->list
);
265 wake_up_process(waiter
->task
);