64ac24e738
Semaphores are no longer performance-critical, so a generic C implementation is better for maintainability, debuggability and extensibility. Thanks to Peter Zijlstra for fixing the lockdep warning. Thanks to Harvey Harrison for pointing out that the unlikely() was unnecessary. Signed-off-by: Matthew Wilcox <willy@linux.intel.com> Acked-by: Ingo Molnar <mingo@elte.hu>
78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
/*
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* Copyright (c) 2008 Intel Corporation
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* Author: Matthew Wilcox <willy@linux.intel.com>
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*
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* Distributed under the terms of the GNU GPL, version 2
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*
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* Counting semaphores allow up to <n> tasks to acquire the semaphore
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* simultaneously.
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*/
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#ifndef __LINUX_SEMAPHORE_H
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#define __LINUX_SEMAPHORE_H
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#include <linux/list.h>
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#include <linux/spinlock.h>
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/*
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* The spinlock controls access to the other members of the semaphore.
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* 'count' is decremented by every task which calls down*() and incremented
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* by every call to up(). Thus, if it is positive, it indicates how many
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* more tasks may acquire the lock. If it is negative, it indicates how
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* many tasks are waiting for the lock. Tasks waiting for the lock are
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* kept on the wait_list.
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*/
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struct semaphore {
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spinlock_t lock;
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int count;
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struct list_head wait_list;
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};
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#define __SEMAPHORE_INITIALIZER(name, n) \
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{ \
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.lock = __SPIN_LOCK_UNLOCKED((name).lock), \
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.count = n, \
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.wait_list = LIST_HEAD_INIT((name).wait_list), \
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}
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#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
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struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
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#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
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static inline void sema_init(struct semaphore *sem, int val)
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{
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static struct lock_class_key __key;
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*sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
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lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0);
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}
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#define init_MUTEX(sem) sema_init(sem, 1)
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#define init_MUTEX_LOCKED(sem) sema_init(sem, 0)
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/*
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* Attempt to acquire the semaphore. If another task is already holding the
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* semaphore, sleep until the semaphore is released.
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*/
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extern void down(struct semaphore *sem);
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/*
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* As down(), except the sleep may be interrupted by a signal. If it is,
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* this function will return -EINTR.
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*/
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extern int __must_check down_interruptible(struct semaphore *sem);
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/*
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* As down(), except this function will not sleep. It will return 0 if it
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* acquired the semaphore and 1 if the semaphore was contended. This
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* function may be called from any context, including interrupt and softirq.
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*/
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extern int __must_check down_trylock(struct semaphore *sem);
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/*
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* Release the semaphore. Unlike mutexes, up() may be called from any
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* context and even by tasks which have never called down().
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*/
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extern void up(struct semaphore *sem);
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#endif /* __LINUX_SEMAPHORE_H */
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