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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#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
64
65static inline void sema_init (struct semaphore *sem, int val)
66{
67/*
68 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
69 *
70 * i'd rather use the more flexible initialization above, but sadly
71 * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
72 */
73 atomic_set(&sem->count, val);
74 sem->sleepers = 0;
75 init_waitqueue_head(&sem->wait);
76}
77
78static inline void init_MUTEX (struct semaphore *sem)
79{
80 sema_init(sem, 1);
81}
82
83static inline void init_MUTEX_LOCKED (struct semaphore *sem)
84{
85 sema_init(sem, 0);
86}
87
88asmlinkage void __down_failed(void /* special register calling convention */);
89asmlinkage int __down_failed_interruptible(void /* params in registers */);
90asmlinkage int __down_failed_trylock(void /* params in registers */);
91asmlinkage void __up_wakeup(void /* special register calling convention */);
92
93asmlinkage void __down(struct semaphore * sem);
94asmlinkage int __down_interruptible(struct semaphore * sem);
95asmlinkage int __down_trylock(struct semaphore * sem);
96asmlinkage void __up(struct semaphore * sem);
97
98/*
99 * This is ugly, but we want the default case to fall through.
100 * "__down_failed" is a special asm handler that calls the C
101 * routine that actually waits. See arch/x86_64/kernel/semaphore.c
102 */
103static inline void down(struct semaphore * sem)
104{
105 might_sleep();
106
107 __asm__ __volatile__(
108 "# atomic down operation\n\t"
109 LOCK "decl %0\n\t" /* --sem->count */
110 "js 2f\n"
111 "1:\n"
112 LOCK_SECTION_START("")
113 "2:\tcall __down_failed\n\t"
114 "jmp 1b\n"
115 LOCK_SECTION_END
116 :"=m" (sem->count)
117 :"D" (sem)
118 :"memory");
119}
120
121/*
122 * Interruptible try to acquire a semaphore. If we obtained
123 * it, return zero. If we were interrupted, returns -EINTR
124 */
125static inline int down_interruptible(struct semaphore * sem)
126{
127 int result;
128
129 might_sleep();
130
131 __asm__ __volatile__(
132 "# atomic interruptible down operation\n\t"
133 LOCK "decl %1\n\t" /* --sem->count */
134 "js 2f\n\t"
135 "xorl %0,%0\n"
136 "1:\n"
137 LOCK_SECTION_START("")
138 "2:\tcall __down_failed_interruptible\n\t"
139 "jmp 1b\n"
140 LOCK_SECTION_END
141 :"=a" (result), "=m" (sem->count)
142 :"D" (sem)
143 :"memory");
144 return result;
145}
146
147/*
148 * Non-blockingly attempt to down() a semaphore.
149 * Returns zero if we acquired it
150 */
151static inline int down_trylock(struct semaphore * sem)
152{
153 int result;
154
155 __asm__ __volatile__(
156 "# atomic interruptible down operation\n\t"
157 LOCK "decl %1\n\t" /* --sem->count */
158 "js 2f\n\t"
159 "xorl %0,%0\n"
160 "1:\n"
161 LOCK_SECTION_START("")
162 "2:\tcall __down_failed_trylock\n\t"
163 "jmp 1b\n"
164 LOCK_SECTION_END
165 :"=a" (result), "=m" (sem->count)
166 :"D" (sem)
167 :"memory","cc");
168 return result;
169}
170
171/*
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().
176 */
177static inline void up(struct semaphore * sem)
178{
179 __asm__ __volatile__(
180 "# atomic up operation\n\t"
181 LOCK "incl %0\n\t" /* ++sem->count */
182 "jle 2f\n"
183 "1:\n"
184 LOCK_SECTION_START("")
185 "2:\tcall __up_wakeup\n\t"
186 "jmp 1b\n"
187 LOCK_SECTION_END
188 :"=m" (sem->count)
189 :"D" (sem)
190 :"memory");
191}
192#endif /* __KERNEL__ */
193#endif