![Linus Torvalds](/assets/img/avatar_default.png)
Use "+m" rather than a combination of "=m" and "m" for improved clarity and consistency. This also fixes some inlines that incorrectly didn't tell the compiler that they read the old value at all, potentially causing the compiler to generate bogus code. It appear that all of those potential bugs were hidden by the use of extra "volatile" specifiers on the data structures in question, though. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
192 lines
5 KiB
C
192 lines
5 KiB
C
#ifndef _I386_SEMAPHORE_H
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#define _I386_SEMAPHORE_H
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#include <linux/linkage.h>
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#ifdef __KERNEL__
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/*
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* SMP- and interrupt-safe semaphores..
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*
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* (C) Copyright 1996 Linus Torvalds
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*
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* Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
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* the original code and to make semaphore waits
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* interruptible so that processes waiting on
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* semaphores can be killed.
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* Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper
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* functions in asm/sempahore-helper.h while fixing a
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* potential and subtle race discovered by Ulrich Schmid
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* in down_interruptible(). Since I started to play here I
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* also implemented the `trylock' semaphore operation.
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* 1999-07-02 Artur Skawina <skawina@geocities.com>
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* Optimized "0(ecx)" -> "(ecx)" (the assembler does not
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* do this). Changed calling sequences from push/jmp to
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* traditional call/ret.
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* Modified 2001-01-01 Andreas Franck <afranck@gmx.de>
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* Some hacks to ensure compatibility with recent
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* GCC snapshots, to avoid stack corruption when compiling
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* with -fomit-frame-pointer. It's not sure if this will
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* be fixed in GCC, as our previous implementation was a
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* bit dubious.
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*
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* If you would like to see an analysis of this implementation, please
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* ftp to gcom.com and download the file
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* /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
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*
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*/
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#include <asm/system.h>
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#include <asm/atomic.h>
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#include <linux/wait.h>
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#include <linux/rwsem.h>
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struct semaphore {
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atomic_t count;
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int sleepers;
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wait_queue_head_t wait;
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};
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#define __SEMAPHORE_INITIALIZER(name, n) \
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{ \
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.count = ATOMIC_INIT(n), \
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.sleepers = 0, \
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.wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
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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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#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
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static inline void sema_init (struct semaphore *sem, int val)
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{
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/*
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* *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
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*
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* i'd rather use the more flexible initialization above, but sadly
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* GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
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*/
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atomic_set(&sem->count, val);
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sem->sleepers = 0;
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init_waitqueue_head(&sem->wait);
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}
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static inline void init_MUTEX (struct semaphore *sem)
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{
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sema_init(sem, 1);
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}
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static inline void init_MUTEX_LOCKED (struct semaphore *sem)
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{
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sema_init(sem, 0);
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}
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fastcall void __down_failed(void /* special register calling convention */);
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fastcall int __down_failed_interruptible(void /* params in registers */);
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fastcall int __down_failed_trylock(void /* params in registers */);
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fastcall void __up_wakeup(void /* special register calling convention */);
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/*
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* This is ugly, but we want the default case to fall through.
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* "__down_failed" is a special asm handler that calls the C
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* routine that actually waits. See arch/i386/kernel/semaphore.c
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*/
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static inline void down(struct semaphore * sem)
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{
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might_sleep();
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__asm__ __volatile__(
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"# atomic down operation\n\t"
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LOCK_PREFIX "decl %0\n\t" /* --sem->count */
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"js 2f\n"
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"1:\n"
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LOCK_SECTION_START("")
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"2:\tlea %0,%%eax\n\t"
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"call __down_failed\n\t"
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"jmp 1b\n"
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LOCK_SECTION_END
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:"+m" (sem->count)
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:
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:"memory","ax");
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}
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/*
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* Interruptible try to acquire a semaphore. If we obtained
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* it, return zero. If we were interrupted, returns -EINTR
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*/
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static inline int down_interruptible(struct semaphore * sem)
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{
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int result;
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might_sleep();
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__asm__ __volatile__(
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"# atomic interruptible down operation\n\t"
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LOCK_PREFIX "decl %1\n\t" /* --sem->count */
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"js 2f\n\t"
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"xorl %0,%0\n"
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"1:\n"
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LOCK_SECTION_START("")
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"2:\tlea %1,%%eax\n\t"
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"call __down_failed_interruptible\n\t"
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"jmp 1b\n"
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LOCK_SECTION_END
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:"=a" (result), "+m" (sem->count)
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:
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:"memory");
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return result;
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}
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/*
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* Non-blockingly attempt to down() a semaphore.
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* Returns zero if we acquired it
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*/
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static inline int down_trylock(struct semaphore * sem)
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{
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int result;
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__asm__ __volatile__(
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"# atomic interruptible down operation\n\t"
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LOCK_PREFIX "decl %1\n\t" /* --sem->count */
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"js 2f\n\t"
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"xorl %0,%0\n"
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"1:\n"
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LOCK_SECTION_START("")
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"2:\tlea %1,%%eax\n\t"
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"call __down_failed_trylock\n\t"
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"jmp 1b\n"
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LOCK_SECTION_END
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:"=a" (result), "+m" (sem->count)
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:
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:"memory");
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return result;
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}
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/*
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* Note! This is subtle. We jump to wake people up only if
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* the semaphore was negative (== somebody was waiting on it).
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* The default case (no contention) will result in NO
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* jumps for both down() and up().
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*/
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static inline void up(struct semaphore * sem)
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{
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__asm__ __volatile__(
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"# atomic up operation\n\t"
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LOCK_PREFIX "incl %0\n\t" /* ++sem->count */
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"jle 2f\n"
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"1:\n"
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LOCK_SECTION_START("")
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"2:\tlea %0,%%eax\n\t"
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"call __up_wakeup\n\t"
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"jmp 1b\n"
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LOCK_SECTION_END
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".subsection 0\n"
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:"+m" (sem->count)
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:
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:"memory","ax");
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}
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#endif
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#endif
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