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_PREFIX "decl %0\n\t"     /* --sem->count */
110		"jns 1f\n\t"
111		"call __down_failed\n"
112		"1:"
113		:"=m" (sem->count)
114		:"D" (sem)
115		:"memory");
116}
117
118/*
119 * Interruptible try to acquire a semaphore.  If we obtained
120 * it, return zero.  If we were interrupted, returns -EINTR
121 */
122static inline int down_interruptible(struct semaphore * sem)
123{
124	int result;
125
126	might_sleep();
127
128	__asm__ __volatile__(
129		"# atomic interruptible down operation\n\t"
130		"xorl %0,%0\n\t"
131		LOCK_PREFIX "decl %1\n\t"     /* --sem->count */
132		"jns 2f\n\t"
133		"call __down_failed_interruptible\n"
134		"2:\n"
135		:"=&a" (result), "=m" (sem->count)
136		:"D" (sem)
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"
151		"xorl %0,%0\n\t"
152		LOCK_PREFIX "decl %1\n\t"     /* --sem->count */
153		"jns 2f\n\t"
154		"call __down_failed_trylock\n\t"
155		"2:\n"
156		:"=&a" (result), "=m" (sem->count)
157		:"D" (sem)
158		:"memory","cc");
159	return result;
160}
161
162/*
163 * Note! This is subtle. We jump to wake people up only if
164 * the semaphore was negative (== somebody was waiting on it).
165 * The default case (no contention) will result in NO
166 * jumps for both down() and up().
167 */
168static inline void up(struct semaphore * sem)
169{
170	__asm__ __volatile__(
171		"# atomic up operation\n\t"
172		LOCK_PREFIX "incl %0\n\t"     /* ++sem->count */
173		"jg 1f\n\t"
174		"call __up_wakeup\n"
175		"1:"
176		:"=m" (sem->count)
177		:"D" (sem)
178		:"memory");
179}
180#endif /* __KERNEL__ */
181#endif
182