include/asm-i386/semaphore.h

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