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1#ifndef _X86_64_SEMAPHORE_H
2#define _X86_64_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 <asm/rwlock.h>
42#include <linux/wait.h>
43#include <linux/rwsem.h>
44#include <linux/stringify.h>
45
46struct semaphore {
47 atomic_t count;
48 int sleepers;
49 wait_queue_head_t wait;
50};
51
52#define __SEMAPHORE_INITIALIZER(name, n) \
53{ \
54 .count = ATOMIC_INIT(n), \
55 .sleepers = 0, \
56 .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
57}
58
59#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
60 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
61
62#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
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
87asmlinkage void __down_failed(void /* special register calling convention */);
88asmlinkage int __down_failed_interruptible(void /* params in registers */);
89asmlinkage int __down_failed_trylock(void /* params in registers */);
90asmlinkage void __up_wakeup(void /* special register calling convention */);
91
92asmlinkage void __down(struct semaphore * sem);
93asmlinkage int __down_interruptible(struct semaphore * sem);
94asmlinkage int __down_trylock(struct semaphore * sem);
95asmlinkage void __up(struct semaphore * sem);
96
97/*
98 * This is ugly, but we want the default case to fall through.
99 * "__down_failed" is a special asm handler that calls the C
100 * routine that actually waits. See arch/x86_64/kernel/semaphore.c
101 */
102static inline void down(struct semaphore * sem)
103{
104 might_sleep();
105
106 __asm__ __volatile__(
107 "# atomic down operation\n\t"
108 LOCK_PREFIX "decl %0\n\t" /* --sem->count */
109 "jns 1f\n\t"
110 "call __down_failed\n"
111 "1:"
112 :"=m" (sem->count)
113 :"D" (sem)
114 :"memory");
115}
116
117/*
118 * Interruptible try to acquire a semaphore. If we obtained
119 * it, return zero. If we were interrupted, returns -EINTR
120 */
121static inline int down_interruptible(struct semaphore * sem)
122{
123 int result;
124
125 might_sleep();
126
127 __asm__ __volatile__(
128 "# atomic interruptible down operation\n\t"
129 "xorl %0,%0\n\t"
130 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
131 "jns 2f\n\t"
132 "call __down_failed_interruptible\n"
133 "2:\n"
134 :"=&a" (result), "=m" (sem->count)
135 :"D" (sem)
136 :"memory");
137 return result;
138}
139
140/*
141 * Non-blockingly attempt to down() a semaphore.
142 * Returns zero if we acquired it
143 */
144static inline int down_trylock(struct semaphore * sem)
145{
146 int result;
147
148 __asm__ __volatile__(
149 "# atomic interruptible down operation\n\t"
150 "xorl %0,%0\n\t"
151 LOCK_PREFIX "decl %1\n\t" /* --sem->count */
152 "jns 2f\n\t"
153 "call __down_failed_trylock\n\t"
154 "2:\n"
155 :"=&a" (result), "=m" (sem->count)
156 :"D" (sem)
157 :"memory","cc");
158 return result;
159}
160
161/*
162 * Note! This is subtle. We jump to wake people up only if
163 * the semaphore was negative (== somebody was waiting on it).
164 * The default case (no contention) will result in NO
165 * jumps for both down() and up().
166 */
167static inline void up(struct semaphore * sem)
168{
169 __asm__ __volatile__(
170 "# atomic up operation\n\t"
171 LOCK_PREFIX "incl %0\n\t" /* ++sem->count */
172 "jg 1f\n\t"
173 "call __up_wakeup\n"
174 "1:"
175 :"=m" (sem->count)
176 :"D" (sem)
177 :"memory");
178}
179#endif /* __KERNEL__ */
180#endif