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 "decl %0\n\t"     /* --sem->count */
 103                 "js 2f\n"
 104                 "1:\n"
 105                 LOCK_SECTION_START("")
 106                 "2:\tlea %0,%%eax\n\t"
 107                 "call __down_failed\n\t"
 108                 "jmp 1b\n"
 109                 LOCK_SECTION_END
 110                 :"=m" (sem->count)
 111                 :
 112                 :"memory","ax");
 113 }
 114
 115 /*
 116  * Interruptible try to acquire a semaphore.  If we obtained
 117  * it, return zero.  If we were interrupted, returns -EINTR
 118  */
 119 static inline int down_interruptible(struct semaphore * sem)
 120 {
 121         int result;
 122
 123         might_sleep();
 124         __asm__ __volatile__(
 125                 "# atomic interruptible down operation\n\t"
 126                 LOCK "decl %1\n\t"     /* --sem->count */
 127                 "js 2f\n\t"
 128                 "xorl %0,%0\n"
 129                 "1:\n"
 130                 LOCK_SECTION_START("")
 131                 "2:\tlea %1,%%eax\n\t"
 132                 "call __down_failed_interruptible\n\t"
 133                 "jmp 1b\n"
 134                 LOCK_SECTION_END
 135                 :"=a" (result), "=m" (sem->count)
 136                 :
 137                 :"memory");
 138         return result;
 139 }
 140
 141 /*
 142  * Non-blockingly attempt to down() a semaphore.
 143  * Returns zero if we acquired it
 144  */
 145 static inline int down_trylock(struct semaphore * sem)
 146 {
 147         int result;
 148
 149         __asm__ __volatile__(
 150                 "# atomic interruptible down operation\n\t"
 151                 LOCK "decl %1\n\t"     /* --sem->count */
 152                 "js 2f\n\t"
 153                 "xorl %0,%0\n"
 154                 "1:\n"
 155                 LOCK_SECTION_START("")
 156                 "2:\tlea %1,%%eax\n\t"
 157                 "call __down_failed_trylock\n\t"
 158                 "jmp 1b\n"
 159                 LOCK_SECTION_END
 160                 :"=a" (result), "=m" (sem->count)
 161                 :
 162                 :"memory");
 163         return result;
 164 }
 165
 166 /*
 167  * Note! This is subtle. We jump to wake people up only if
 168  * the semaphore was negative (== somebody was waiting on it).
 169  * The default case (no contention) will result in NO
 170  * jumps for both down() and up().
 171  */
 172 static inline void up(struct semaphore * sem)
 173 {
 174         __asm__ __volatile__(
 175                 "# atomic up operation\n\t"
 176                 LOCK "incl %0\n\t"     /* ++sem->count */
 177                 "jle 2f\n"
 178                 "1:\n"
 179                 LOCK_SECTION_START("")
 180                 "2:\tlea %0,%%eax\n\t"
 181                 "call __up_wakeup\n\t"
 182                 "jmp 1b\n"
 183                 LOCK_SECTION_END
 184                 ".subsection 0\n"
 185                 :"=m" (sem->count)
 186                 :
 187                 :"memory","ax");
 188 }
 189
 190 #endif
 191 #endif