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