1 #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 (at) 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 (at) 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 (at) 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 44 struct 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 58 #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 63 static inline void sema_init (struct semaphore *sem, int val) 64 { 65 /* 66 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val); 67 * 68 * i'd rather use the more flexible initialization above, but sadly 69 * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well. 70 */ 71 atomic_set(&sem->count, val); 72 sem->sleepers = 0; 73 init_waitqueue_head(&sem->wait); 74 } 75 76 static inline void init_MUTEX (struct semaphore *sem) 77 { 78 sema_init(sem, 1); 79 } 80 81 static inline void init_MUTEX_LOCKED (struct semaphore *sem) 82 { 83 sema_init(sem, 0); 84 } 85 86 fastcall void __down_failed(void /* special register calling convention */); 87 fastcall int __down_failed_interruptible(void /* params in registers */); 88 fastcall int __down_failed_trylock(void /* params in registers */); 89 fastcall void __up_wakeup(void /* special register calling convention */); 90 91 /* 92 * This is ugly, but we want the default case to fall through. 93 * "__down_failed" is a special asm handler that calls the C 94 * routine that actually waits. See arch/i386/kernel/semaphore.c 95 */ 96 static inline void down(struct semaphore * sem) 97 { 98 might_sleep(); 99 __asm__ __volatile__( 100 "# atomic down operation\n\t" 101 LOCK_PREFIX "decl %0\n\t" /* --sem->count */ 102 "jns 2f\n" 103 "\tlea %0,%%eax\n\t" 104 "call __down_failed\n" 105 "2:" 106 :"+m" (sem->count) 107 : 108 :"memory","ax"); 109 } 110 111 /* 112 * Interruptible try to acquire a semaphore. If we obtained 113 * it, return zero. If we were interrupted, returns -EINTR 114 */ 115 static inline int down_interruptible(struct semaphore * sem) 116 { 117 int result; 118 119 might_sleep(); 120 __asm__ __volatile__( 121 "# atomic interruptible down operation\n\t" 122 "xorl %0,%0\n\t" 123 LOCK_PREFIX "decl %1\n\t" /* --sem->count */ 124 "jns 2f\n\t" 125 "lea %1,%%eax\n\t" 126 "call __down_failed_interruptible\n" 127 "2:" 128 :"=&a" (result), "+m" (sem->count) 129 : 130 :"memory"); 131 return result; 132 } 133 134 /* 135 * Non-blockingly attempt to down() a semaphore. 136 * Returns zero if we acquired it 137 */ 138 static inline int down_trylock(struct semaphore * sem) 139 { 140 int result; 141 142 __asm__ __volatile__( 143 "# atomic interruptible down operation\n\t" 144 "xorl %0,%0\n\t" 145 LOCK_PREFIX "decl %1\n\t" /* --sem->count */ 146 "jns 2f\n\t" 147 "lea %1,%%eax\n\t" 148 "call __down_failed_trylock\n\t" 149 "2:\n" 150 :"=&a" (result), "+m" (sem->count) 151 : 152 :"memory"); 153 return result; 154 } 155 156 /* 157 * Note! This is subtle. We jump to wake people up only if 158 * the semaphore was negative (== somebody was waiting on it). 159 */ 160 static inline void up(struct semaphore * sem) 161 { 162 __asm__ __volatile__( 163 "# atomic up operation\n\t" 164 LOCK_PREFIX "incl %0\n\t" /* ++sem->count */ 165 "jg 1f\n\t" 166 "lea %0,%%eax\n\t" 167 "call __up_wakeup\n" 168 "1:" 169 :"+m" (sem->count) 170 : 171 :"memory","ax"); 172 } 173 174 #endif 175 #endif 176
