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Generic semaphore implementation

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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>
This commit is contained in:
Matthew Wilcox
2008-03-07 21:55:58 -05:00
committed by Matthew Wilcox
parent e48b3deee4
commit 64ac24e738
113 changed files with 314 additions and 7679 deletions
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109
include/asm-mips/semaphore.h
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@@ -1,108 +1 @@
/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 1996 Linus Torvalds
* Copyright (C) 1998, 99, 2000, 01, 04 Ralf Baechle
* Copyright (C) 1999, 2000, 01 Silicon Graphics, Inc.
* Copyright (C) 2000, 01 MIPS Technologies, Inc.
*
* In all honesty, little of the old MIPS code left - the PPC64 variant was
* just looking nice and portable so I ripped it. Credits to whoever wrote
* it.
*/
#ifndef __ASM_SEMAPHORE_H
#define __ASM_SEMAPHORE_H
/*
* Remove spinlock-based RW semaphores; RW semaphore definitions are
* now in rwsem.h and we use the generic lib/rwsem.c implementation.
* Rework semaphores to use atomic_dec_if_positive.
* -- Paul Mackerras (paulus@samba.org)
*/
#ifdef __KERNEL__
#include <asm/atomic.h>
#include <asm/system.h>
#include <linux/wait.h>
#include <linux/rwsem.h>
struct semaphore {
/*
* Note that any negative value of count is equivalent to 0,
* but additionally indicates that some process(es) might be
* sleeping on `wait'.
*/
atomic_t count;
wait_queue_head_t wait;
};
#define __SEMAPHORE_INITIALIZER(name, n) \
{ \
.count = ATOMIC_INIT(n), \
.wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
}
#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
static inline void sema_init(struct semaphore *sem, int val)
{
atomic_set(&sem->count, val);
init_waitqueue_head(&sem->wait);
}
static inline void init_MUTEX(struct semaphore *sem)
{
sema_init(sem, 1);
}
static inline void init_MUTEX_LOCKED(struct semaphore *sem)
{
sema_init(sem, 0);
}
extern void __down(struct semaphore * sem);
extern int __down_interruptible(struct semaphore * sem);
extern void __up(struct semaphore * sem);
static inline void down(struct semaphore * sem)
{
might_sleep();
/*
* Try to get the semaphore, take the slow path if we fail.
*/
if (unlikely(atomic_dec_return(&sem->count) < 0))
__down(sem);
}
static inline int down_interruptible(struct semaphore * sem)
{
int ret = 0;
might_sleep();
if (unlikely(atomic_dec_return(&sem->count) < 0))
ret = __down_interruptible(sem);
return ret;
}
static inline int down_trylock(struct semaphore * sem)
{
return atomic_dec_if_positive(&sem->count) < 0;
}
static inline void up(struct semaphore * sem)
{
if (unlikely(atomic_inc_return(&sem->count) <= 0))
__up(sem);
}
#endif /* __KERNEL__ */
#endif /* __ASM_SEMAPHORE_H */
#include <linux/semaphore.h>