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Generic semaphore implementation

Browse source 
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 <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
This commit is contained in:
Matthew Wilcox 2008-03-07 21:55:58 -05:00 • committed by Matthew Wilcox
commit 64ac24e738
113 changed files with 314 additions and 7679 deletions
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108
include/asm-s390/semaphore.h
View file

@ -1,107 +1 @@
/*
* include/asm-s390/semaphore.h
*
* S390 version
* Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
*
* Derived from "include/asm-i386/semaphore.h"
* (C) Copyright 1996 Linus Torvalds
*/
#ifndef _S390_SEMAPHORE_H
#define _S390_SEMAPHORE_H
#include <asm/system.h>
#include <asm/atomic.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,count) \
{ ATOMIC_INIT(count), __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);
}
asmlinkage void __down(struct semaphore * sem);
asmlinkage int __down_interruptible(struct semaphore * sem);
asmlinkage int __down_trylock(struct semaphore * sem);
asmlinkage void __up(struct semaphore * sem);
static inline void down(struct semaphore * sem)
{
might_sleep();
if (atomic_dec_return(&sem->count) < 0)
__down(sem);
}
static inline int down_interruptible(struct semaphore * sem)
{
int ret = 0;
might_sleep();
if (atomic_dec_return(&sem->count) < 0)
ret = __down_interruptible(sem);
return ret;
}
static inline int down_trylock(struct semaphore * sem)
{
int old_val, new_val;
/*
* This inline assembly atomically implements the equivalent
* to the following C code:
* old_val = sem->count.counter;
* if ((new_val = old_val) > 0)
* sem->count.counter = --new_val;
* In the ppc code this is called atomic_dec_if_positive.
*/
asm volatile(
" l %0,0(%3)\n"
"0: ltr %1,%0\n"
" jle 1f\n"
" ahi %1,-1\n"
" cs %0,%1,0(%3)\n"
" jl 0b\n"
"1:"
: "=&d" (old_val), "=&d" (new_val), "=m" (sem->count.counter)
: "a" (&sem->count.counter), "m" (sem->count.counter)
: "cc", "memory");
return old_val <= 0;
}
static inline void up(struct semaphore * sem)
{
if (atomic_inc_return(&sem->count) <= 0)
__up(sem);
}
#endif
#include <linux/semaphore.h>