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git.proxmox.com Git - mirror_ubuntu-eoan-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/export.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 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 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 * @jiffies: 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 jiffies
)
160 raw_spin_lock_irqsave(&sem
->lock
, flags
);
161 if (likely(sem
->count
> 0))
164 result
= __down_timeout(sem
, jiffies
);
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 task_struct
*task
= current
;
208 struct semaphore_waiter waiter
;
210 list_add_tail(&waiter
.list
, &sem
->wait_list
);
215 if (signal_pending_state(state
, task
))
219 __set_task_state(task
, state
);
220 raw_spin_unlock_irq(&sem
->lock
);
221 timeout
= schedule_timeout(timeout
);
222 raw_spin_lock_irq(&sem
->lock
);
228 list_del(&waiter
.list
);
232 list_del(&waiter
.list
);
236 static noinline
void __sched
__down(struct semaphore
*sem
)
238 __down_common(sem
, TASK_UNINTERRUPTIBLE
, MAX_SCHEDULE_TIMEOUT
);
241 static noinline
int __sched
__down_interruptible(struct semaphore
*sem
)
243 return __down_common(sem
, TASK_INTERRUPTIBLE
, MAX_SCHEDULE_TIMEOUT
);
246 static noinline
int __sched
__down_killable(struct semaphore
*sem
)
248 return __down_common(sem
, TASK_KILLABLE
, MAX_SCHEDULE_TIMEOUT
);
251 static noinline
int __sched
__down_timeout(struct semaphore
*sem
, long jiffies
)
253 return __down_common(sem
, TASK_UNINTERRUPTIBLE
, jiffies
);
256 static noinline
void __sched
__up(struct semaphore
*sem
)
258 struct semaphore_waiter
*waiter
= list_first_entry(&sem
->wait_list
,
259 struct semaphore_waiter
, list
);
260 list_del(&waiter
->list
);
262 wake_up_process(waiter
->task
);