include/asm-i386/semaphore.h

   1 #ifndef _I386_SEMAPHORE_H
   2 #define _I386_SEMAPHORE_H
   3
   4 #include <linux/linkage.h>
   5
   6 #ifdef __SMP__
   7 extern void __check_locks(unsigned int);
   8 #else
   9 #define __check_locks(x)        do { } while (0)
  10 #endif
  11
  12 /*
  13  * SMP- and interrupt-safe semaphores..
  14  *
  15  * (C) Copyright 1996 Linus Torvalds
  16  *
  17  * Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
  18  *                     the original code and to make semaphore waits
  19  *                     interruptible so that processes waiting on
  20  *                     semaphores can be killed.
  21  *
  22  * If you would like to see an analysis of this implementation, please
  23  * ftp to gcom.com and download the file
  24  * /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
  25  *
  26  */
  27
  28 #include <asm/system.h>
  29 #include <asm/atomic.h>
  30 #include <asm/spinlock.h>
  31
  32 struct semaphore {
  33         atomic_t count;
  34         int waking;
  35         struct wait_queue * wait;
  36 };
  37
  38 #define MUTEX ((struct semaphore) { ATOMIC_INIT(1), 0, NULL })
  39 #define MUTEX_LOCKED ((struct semaphore) { ATOMIC_INIT(0), 0, NULL })
  40
  41 asmlinkage void __down_failed(void /* special register calling convention */);
  42 asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
  43 asmlinkage void __up_wakeup(void /* special register calling convention */);
  44
  45 extern void __down(struct semaphore * sem);
  46 extern void __up(struct semaphore * sem);
  47
  48 extern spinlock_t semaphore_wake_lock;
  49
  50 #define sema_init(sem, val)     atomic_set(&((sem)->count), (val))
  51
  52 /*
  53  * These two _must_ execute atomically wrt each other.
  54  *
  55  * This is trivially done with load_locked/store_cond,
  56  * but on the x86 we need an external synchronizer.
  57  * Currently this is just the global interrupt lock,
  58  * bah. Go for a smaller spinlock some day.
  59  *
  60  * (On the other hand this shouldn't be in any critical
  61  * path, so..)
  62  */
  63 static inline void wake_one_more(struct semaphore * sem)
  64 {
  65         unsigned long flags;
  66
  67         spin_lock_irqsave(&semaphore_wake_lock, flags);
  68         sem->waking++;
  69         spin_unlock_irqrestore(&semaphore_wake_lock, flags);
  70 }
  71
  72 static inline int waking_non_zero(struct semaphore *sem)
  73 {
  74         unsigned long flags;
  75         int ret = 0;
  76
  77         spin_lock_irqsave(&semaphore_wake_lock, flags);
  78         if (sem->waking > 0) {
  79                 sem->waking--;
  80                 ret = 1;
  81         }
  82         spin_unlock_irqrestore(&semaphore_wake_lock, flags);
  83         return ret;
  84 }
  85
  86 /*
  87  * This is ugly, but we want the default case to fall through.
  88  * "down_failed" is a special asm handler that calls the C
  89  * routine that actually waits. See arch/i386/lib/semaphore.S
  90  */
  91 extern inline void down(struct semaphore * sem)
  92 {
  93         __check_locks(0);
  94         __asm__ __volatile__(
  95                 "# atomic down operation\n\t"
  96 #ifdef __SMP__
  97                 "lock ; "
  98 #endif
  99                 "decl 0(%0)\n\t"
 100                 "js 2f\n"
 101                 "1:\n"
 102                 ".section .text.lock,\"ax\"\n"
 103                 "2:\tpushl $1b\n\t"
 104                 "jmp __down_failed\n"
 105                 ".previous"
 106                 :/* no outputs */
 107                 :"c" (sem)
 108                 :"memory");
 109 }
 110
 111 extern inline int down_interruptible(struct semaphore * sem)
 112 {
 113         int result;
 114
 115         __check_locks(0);
 116         __asm__ __volatile__(
 117                 "# atomic interruptible down operation\n\t"
 118 #ifdef __SMP__
 119                 "lock ; "
 120 #endif
 121                 "decl 0(%1)\n\t"
 122                 "js 2f\n\t"
 123                 "xorl %0,%0\n"
 124                 "1:\n"
 125                 ".section .text.lock,\"ax\"\n"
 126                 "2:\tpushl $1b\n\t"
 127                 "jmp __down_failed_interruptible\n"
 128                 ".previous"
 129                 :"=a" (result)
 130                 :"c" (sem)
 131                 :"memory");
 132         return result;
 133 }
 134
 135
 136 /*
 137  * Note! This is subtle. We jump to wake people up only if
 138  * the semaphore was negative (== somebody was waiting on it).
 139  * The default case (no contention) will result in NO
 140  * jumps for both down() and up().
 141  */
 142 extern inline void up(struct semaphore * sem)
 143 {
 144         __asm__ __volatile__(
 145                 "# atomic up operation\n\t"
 146 #ifdef __SMP__
 147                 "lock ; "
 148 #endif
 149                 "incl 0(%0)\n\t"
 150                 "jle 2f\n"
 151                 "1:\n"
 152                 ".section .text.lock,\"ax\"\n"
 153                 "2:\tpushl $1b\n\t"
 154                 "jmp __up_wakeup\n"
 155                 ".previous"
 156                 :/* no outputs */
 157                 :"c" (sem)
 158                 :"memory");
 159 }
 160
 161 #endif