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Linus Torvalds1da177e2005-04-16 15:20:36 -07001#ifndef _I386_SEMAPHORE_H
2#define _I386_SEMAPHORE_H
3
4#include <linux/linkage.h>
5
6#ifdef __KERNEL__
7
8/*
9 * SMP- and interrupt-safe semaphores..
10 *
11 * (C) Copyright 1996 Linus Torvalds
12 *
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
31 * bit dubious.
32 *
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.
36 *
37 */
38
39#include <asm/system.h>
40#include <asm/atomic.h>
41#include <linux/wait.h>
42#include <linux/rwsem.h>
43
44struct semaphore {
45 atomic_t count;
46 int sleepers;
47 wait_queue_head_t wait;
48};
49
50
51#define __SEMAPHORE_INITIALIZER(name, n) \
52{ \
53 .count = ATOMIC_INIT(n), \
54 .sleepers = 0, \
55 .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
56}
57
Linus Torvalds1da177e2005-04-16 15:20:36 -070058#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
59 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
60
61#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
62#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
63
64static inline void sema_init (struct semaphore *sem, int val)
65{
66/*
67 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
68 *
69 * i'd rather use the more flexible initialization above, but sadly
70 * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
71 */
72 atomic_set(&sem->count, val);
73 sem->sleepers = 0;
74 init_waitqueue_head(&sem->wait);
75}
76
77static inline void init_MUTEX (struct semaphore *sem)
78{
79 sema_init(sem, 1);
80}
81
82static inline void init_MUTEX_LOCKED (struct semaphore *sem)
83{
84 sema_init(sem, 0);
85}
86
87fastcall void __down_failed(void /* special register calling convention */);
88fastcall int __down_failed_interruptible(void /* params in registers */);
89fastcall int __down_failed_trylock(void /* params in registers */);
90fastcall void __up_wakeup(void /* special register calling convention */);
91
92/*
93 * This is ugly, but we want the default case to fall through.
94 * "__down_failed" is a special asm handler that calls the C
95 * routine that actually waits. See arch/i386/kernel/semaphore.c
96 */
97static inline void down(struct semaphore * sem)
98{
99 might_sleep();
100 __asm__ __volatile__(
101 "# atomic down operation\n\t"
Gerd Hoffmann9a0b5812006-03-23 02:59:32 -0800102 LOCK_PREFIX "decl %0\n\t" /* --sem->count */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103 "js 2f\n"
104 "1:\n"
105 LOCK_SECTION_START("")
106 "2:\tlea %0,%%eax\n\t"
107 "call __down_failed\n\t"
108 "jmp 1b\n"
109 LOCK_SECTION_END
110 :"=m" (sem->count)
111 :
112 :"memory","ax");
113}
114
115/*
116 * Interruptible try to acquire a semaphore. If we obtained
117 * it, return zero. If we were interrupted, returns -EINTR
118 */
119static inline int down_interruptible(struct semaphore * sem)
120{
121 int result;
122
123 might_sleep();
124 __asm__ __volatile__(
125 "# atomic interruptible down operation\n\t"
Gerd Hoffmann9a0b5812006-03-23 02:59:32 -0800126 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127 "js 2f\n\t"
128 "xorl %0,%0\n"
129 "1:\n"
130 LOCK_SECTION_START("")
131 "2:\tlea %1,%%eax\n\t"
132 "call __down_failed_interruptible\n\t"
133 "jmp 1b\n"
134 LOCK_SECTION_END
135 :"=a" (result), "=m" (sem->count)
136 :
137 :"memory");
138 return result;
139}
140
141/*
142 * Non-blockingly attempt to down() a semaphore.
143 * Returns zero if we acquired it
144 */
145static inline int down_trylock(struct semaphore * sem)
146{
147 int result;
148
149 __asm__ __volatile__(
150 "# atomic interruptible down operation\n\t"
Gerd Hoffmann9a0b5812006-03-23 02:59:32 -0800151 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152 "js 2f\n\t"
153 "xorl %0,%0\n"
154 "1:\n"
155 LOCK_SECTION_START("")
156 "2:\tlea %1,%%eax\n\t"
157 "call __down_failed_trylock\n\t"
158 "jmp 1b\n"
159 LOCK_SECTION_END
160 :"=a" (result), "=m" (sem->count)
161 :
162 :"memory");
163 return result;
164}
165
166/*
167 * Note! This is subtle. We jump to wake people up only if
168 * the semaphore was negative (== somebody was waiting on it).
169 * The default case (no contention) will result in NO
170 * jumps for both down() and up().
171 */
172static inline void up(struct semaphore * sem)
173{
174 __asm__ __volatile__(
175 "# atomic up operation\n\t"
Gerd Hoffmann9a0b5812006-03-23 02:59:32 -0800176 LOCK_PREFIX "incl %0\n\t" /* ++sem->count */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177 "jle 2f\n"
178 "1:\n"
179 LOCK_SECTION_START("")
180 "2:\tlea %0,%%eax\n\t"
181 "call __up_wakeup\n\t"
182 "jmp 1b\n"
183 LOCK_SECTION_END
184 ".subsection 0\n"
185 :"=m" (sem->count)
186 :
187 :"memory","ax");
188}
189
190#endif
191#endif