1 #ifndef _I386_SEMAPHORE_H
2 #define _I386_SEMAPHORE_H
4 #include <linux/linkage.h>
9 * SMP- and interrupt-safe semaphores..
11 * (C) Copyright 1996 Linus Torvalds
13 * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
14 * the original code and to make semaphore waits
15 * interruptible so that processes waiting on
16 * semaphores can be killed.
17 * Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper
18 * functions in asm/sempahore-helper.h while fixing a
19 * potential and subtle race discovered by Ulrich Schmid
20 * in down_interruptible(). Since I started to play here I
21 * also implemented the `trylock' semaphore operation.
22 * 1999-07-02 Artur Skawina <skawina@geocities.com>
23 * Optimized "0(ecx)" -> "(ecx)" (the assembler does not
24 * do this). Changed calling sequences from push/jmp to
25 * traditional call/ret.
26 * Modified 2001-01-01 Andreas Franck <afranck@gmx.de>
27 * Some hacks to ensure compatibility with recent
28 * GCC snapshots, to avoid stack corruption when compiling
29 * with -fomit-frame-pointer. It's not sure if this will
30 * be fixed in GCC, as our previous implementation was a
33 * If you would like to see an analysis of this implementation, please
34 * ftp to gcom.com and download the file
35 * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
39 #include <asm/system.h>
40 #include <asm/atomic.h>
41 #include <linux/wait.h>
42 #include <linux/rwsem.h>
47 wait_queue_head_t wait;
51 #define __SEMAPHORE_INITIALIZER(name, n) \
53 .count = ATOMIC_INIT(n), \
55 .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
58 #define __MUTEX_INITIALIZER(name) \
59 __SEMAPHORE_INITIALIZER(name,1)
61 #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
62 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
64 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
65 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
67 static inline void sema_init (struct semaphore *sem, int val)
70 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
72 * i'd rather use the more flexible initialization above, but sadly
73 * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
75 atomic_set(&sem->count, val);
77 init_waitqueue_head(&sem->wait);
80 static inline void init_MUTEX (struct semaphore *sem)
85 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
90 asmlinkage void __down_failed(void /* special register calling convention */);
91 asmlinkage int __down_failed_interruptible(void /* params in registers */);
92 asmlinkage int __down_failed_trylock(void /* params in registers */);
93 asmlinkage void __up_wakeup(void /* special register calling convention */);
95 asmlinkage void __down(struct semaphore * sem);
96 asmlinkage int __down_interruptible(struct semaphore * sem);
97 asmlinkage int __down_trylock(struct semaphore * sem);
98 asmlinkage void __up(struct semaphore * sem);
101 * This is ugly, but we want the default case to fall through.
102 * "__down_failed" is a special asm handler that calls the C
103 * routine that actually waits. See arch/i386/kernel/semaphore.c
105 static inline void down(struct semaphore * sem)
108 __asm__ __volatile__(
109 "# atomic down operation\n\t"
110 LOCK "decl %0\n\t" /* --sem->count */
113 LOCK_SECTION_START("")
114 "2:\tcall __down_failed\n\t"
123 * Interruptible try to acquire a semaphore. If we obtained
124 * it, return zero. If we were interrupted, returns -EINTR
126 static inline int down_interruptible(struct semaphore * sem)
131 __asm__ __volatile__(
132 "# atomic interruptible down operation\n\t"
133 LOCK "decl %1\n\t" /* --sem->count */
137 LOCK_SECTION_START("")
138 "2:\tcall __down_failed_interruptible\n\t"
141 :"=a" (result), "=m" (sem->count)
148 * Non-blockingly attempt to down() a semaphore.
149 * Returns zero if we acquired it
151 static inline int down_trylock(struct semaphore * sem)
155 __asm__ __volatile__(
156 "# atomic interruptible down operation\n\t"
157 LOCK "decl %1\n\t" /* --sem->count */
161 LOCK_SECTION_START("")
162 "2:\tcall __down_failed_trylock\n\t"
165 :"=a" (result), "=m" (sem->count)
172 * Note! This is subtle. We jump to wake people up only if
173 * the semaphore was negative (== somebody was waiting on it).
174 * The default case (no contention) will result in NO
175 * jumps for both down() and up().
177 static inline void up(struct semaphore * sem)
179 __asm__ __volatile__(
180 "# atomic up operation\n\t"
181 LOCK "incl %0\n\t" /* ++sem->count */
184 LOCK_SECTION_START("")
185 "2:\tcall __up_wakeup\n\t"