include/asm-i386/semaphore.h

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 1 #ifndef _I386_SEMAPHORE_H
 2 #define _I386_SEMAPHORE_H
 3
 4 #include <linux/linkage.h>
 5
 6 /*
 7  * SMP- and interrupt-safe semaphores..
 8  *
 9  * (C) Copyright 1996 Linus Torvalds
 10  *
 11  * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
 12  * the original code and to make semaphore waits
 13  * interruptible so that processes waiting on
 14  * semaphores can be killed.
 15  * Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper
 16  * functions in asm/sempahore-helper.h while fixing a
 17  * potential and subtle race discovered by Ulrich Schmid
 18  * in down_interruptible(). Since I started to play here I
 19  * also implemented the `trylock' semaphore operation.
 20  *
 21  * If you would like to see an analysis of this implementation, please
 22  * ftp to gcom.com and download the file
 23  * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
 24  *
 25  */
 26
 27 #include <asm/system.h>
 28 #include <asm/atomic.h>
 29 #include <asm/spinlock.h>
 30
 31 struct semaphore {
 32  atomic_t count;
 33 int waking;
 34 struct wait_queue * wait;
 35 };
 36
 37 #define MUTEX ((struct semaphore) { ATOMIC_INIT(1), 0, NULL })
 38 #define MUTEX_LOCKED ((struct semaphore) { ATOMIC_INIT(0), 0, NULL })
 39
 40 asmlinkage void__down_failed(void/* special register calling convention */);
 41 asmlinkage int__down_failed_interruptible(void/* params in registers */);
 42 asmlinkage int__down_failed_trylock(void/* params in registers */);
 43 asmlinkage void__up_wakeup(void/* special register calling convention */);
 44
 45 asmlinkage void__down(struct semaphore * sem);
 46 asmlinkage int__down_interruptible(struct semaphore * sem);
 47 asmlinkage int__down_trylock(struct semaphore * sem);
 48 asmlinkage void__up(struct semaphore * sem);
 49
 50 extern spinlock_t semaphore_wake_lock;
 51
 52 #define sema_init(sem, val) atomic_set(&((sem)->count), (val))
 53
 54 /*
 55  * This is ugly, but we want the default case to fall through.
 56  * "down_failed" is a special asm handler that calls the C
 57  * routine that actually waits. See arch/i386/lib/semaphore.S
 58  */
 59 extern inlinevoiddown(struct semaphore * sem)
 60 {
 61  __asm__ __volatile__(
 62 "# atomic down operation\n\t"
 63 #ifdef __SMP__
 64 "lock ; "
 65 #endif
 66 "decl 0(%0)\n\t"
 67 "js 2f\n"
 68 "1:\n"
 69 ".section .text.lock,\"ax\"\n"
 70 "2:\tpushl $1b\n\t"
 71 "jmp __down_failed\n"
 72 ".previous"
 73 :/* no outputs */
 74 :"c"(sem)
 75 :"memory");
 76 }
 77
 78 extern inlineintdown_interruptible(struct semaphore * sem)
 79 {
 80 int result;
 81
 82  __asm__ __volatile__(
 83 "# atomic interruptible down operation\n\t"
 84 #ifdef __SMP__
 85 "lock ; "
 86 #endif
 87 "decl 0(%1)\n\t"
 88 "js 2f\n\t"
 89 "xorl %0,%0\n"
 90 "1:\n"
 91 ".section .text.lock,\"ax\"\n"
 92 "2:\tpushl $1b\n\t"
 93 "jmp __down_failed_interruptible\n"
 94 ".previous"
 95 :"=a"(result)
 96 :"c"(sem)
 97 :"memory");
 98 return result;
 99 }
 100
 101 extern inlineintdown_trylock(struct semaphore * sem)
 102 {
 103 int result;
 104
 105  __asm__ __volatile__(
 106 "# atomic interruptible down operation\n\t"
 107 #ifdef __SMP__
 108 "lock ; "
 109 #endif
 110 "decl 0(%1)\n\t"
 111 "js 2f\n\t"
 112 "xorl %0,%0\n"
 113 "1:\n"
 114 ".section .text.lock,\"ax\"\n"
 115 "2:\tpushl $1b\n\t"
 116 "jmp __down_failed_trylock\n"
 117 ".previous"
 118 :"=a"(result)
 119 :"c"(sem)
 120 :"memory");
 121 return result;
 122 }
 123
 124 /*
 125  * Note! This is subtle. We jump to wake people up only if
 126  * the semaphore was negative (== somebody was waiting on it).
 127  * The default case (no contention) will result in NO
 128  * jumps for both down() and up().
 129  */
 130 extern inlinevoidup(struct semaphore * sem)
 131 {
 132  __asm__ __volatile__(
 133 "# atomic up operation\n\t"
 134 #ifdef __SMP__
 135 "lock ; "
 136 #endif
 137 "incl 0(%0)\n\t"
 138 "jle 2f\n"
 139 "1:\n"
 140 ".section .text.lock,\"ax\"\n"
 141 "2:\tpushl $1b\n\t"
 142 "jmp __up_wakeup\n"
 143 ".previous"
 144 :/* no outputs */
 145 :"c"(sem)
 146 :"memory");
 147 }
 148
 149 #endif