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 #ifdef WAITQUEUE_DEBUG
  49         long __magic;
  50 #endif
  51 };
  52
  53 #ifdef WAITQUEUE_DEBUG
  54 # define __SEM_DEBUG_INIT(name) \
  55                 , (int)&(name).__magic
  56 #else
  57 # define __SEM_DEBUG_INIT(name)
  58 #endif
  59
  60 #define __SEMAPHORE_INITIALIZER(name,count) \
  61 { ATOMIC_INIT(count), 0, __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
  62         __SEM_DEBUG_INIT(name) }
  63
  64 #define __MUTEX_INITIALIZER(name) \
  65         __SEMAPHORE_INITIALIZER(name,1)
  66
  67 #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
  68         struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
  69
  70 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
  71 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
  72
  73 static inline void sema_init (struct semaphore *sem, int val)
  74 {
  75 /*
  76  *      *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
  77  *
  78  * i'd rather use the more flexible initialization above, but sadly
  79  * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
  80  */
  81         atomic_set(&sem->count, val);
  82         sem->sleepers = 0;
  83         init_waitqueue_head(&sem->wait);
  84 #ifdef WAITQUEUE_DEBUG
  85         sem->__magic = (int)&sem->__magic;
  86 #endif
  87 }
  88
  89 static inline void init_MUTEX (struct semaphore *sem)
  90 {
  91         sema_init(sem, 1);
  92 }
  93
  94 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
  95 {
  96         sema_init(sem, 0);
  97 }
  98
  99 asmlinkage void __down_failed(void /* special register calling convention */);
 100 asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
 101 asmlinkage int  __down_failed_trylock(void  /* params in registers */);
 102 asmlinkage void __up_wakeup(void /* special register calling convention */);
 103
 104 asmlinkage void __down(struct semaphore * sem);
 105 asmlinkage int  __down_interruptible(struct semaphore * sem);
 106 asmlinkage int  __down_trylock(struct semaphore * sem);
 107 asmlinkage void __up(struct semaphore * sem);
 108
 109 /*
 110  * This is ugly, but we want the default case to fall through.
 111  * "__down_failed" is a special asm handler that calls the C
 112  * routine that actually waits. See arch/i386/kernel/semaphore.c
 113  */
 114 static inline void down(struct semaphore * sem)
 115 {
 116 #ifdef WAITQUEUE_DEBUG
 117         CHECK_MAGIC(sem->__magic);
 118 #endif
 119         might_sleep();
 120         __asm__ __volatile__(
 121                 "# atomic down operation\n\t"
 122                 LOCK "decl %0\n\t"     /* --sem->count */
 123                 "js 2f\n"
 124                 "1:\n"
 125                 LOCK_SECTION_START("")
 126                 "2:\tcall __down_failed\n\t"
 127                 "jmp 1b\n"
 128                 LOCK_SECTION_END
 129                 :"=m" (sem->count)
 130                 :"c" (sem)
 131                 :"memory");
 132 }
 133
 134 /*
 135  * Interruptible try to acquire a semaphore.  If we obtained
 136  * it, return zero.  If we were interrupted, returns -EINTR
 137  */
 138 static inline int down_interruptible(struct semaphore * sem)
 139 {
 140         int result;
 141
 142 #ifdef WAITQUEUE_DEBUG
 143         CHECK_MAGIC(sem->__magic);
 144 #endif
 145         might_sleep();
 146         __asm__ __volatile__(
 147                 "# atomic interruptible down operation\n\t"
 148                 LOCK "decl %1\n\t"     /* --sem->count */
 149                 "js 2f\n\t"
 150                 "xorl %0,%0\n"
 151                 "1:\n"
 152                 LOCK_SECTION_START("")
 153                 "2:\tcall __down_failed_interruptible\n\t"
 154                 "jmp 1b\n"
 155                 LOCK_SECTION_END
 156                 :"=a" (result), "=m" (sem->count)
 157                 :"c" (sem)
 158                 :"memory");
 159         return result;
 160 }
 161
 162 /*
 163  * Non-blockingly attempt to down() a semaphore.
 164  * Returns zero if we acquired it
 165  */
 166 static inline int down_trylock(struct semaphore * sem)
 167 {
 168         int result;
 169
 170 #ifdef WAITQUEUE_DEBUG
 171         CHECK_MAGIC(sem->__magic);
 172 #endif
 173
 174         __asm__ __volatile__(
 175                 "# atomic interruptible down operation\n\t"
 176                 LOCK "decl %1\n\t"     /* --sem->count */
 177                 "js 2f\n\t"
 178                 "xorl %0,%0\n"
 179                 "1:\n"
 180                 LOCK_SECTION_START("")
 181                 "2:\tcall __down_failed_trylock\n\t"
 182                 "jmp 1b\n"
 183                 LOCK_SECTION_END
 184                 :"=a" (result), "=m" (sem->count)
 185                 :"c" (sem)
 186                 :"memory");
 187         return result;
 188 }
 189
 190 /*
 191  * Note! This is subtle. We jump to wake people up only if
 192  * the semaphore was negative (== somebody was waiting on it).
 193  * The default case (no contention) will result in NO
 194  * jumps for both down() and up().
 195  */
 196 static inline void up(struct semaphore * sem)
 197 {
 198 #ifdef WAITQUEUE_DEBUG
 199         CHECK_MAGIC(sem->__magic);
 200 #endif
 201         __asm__ __volatile__(
 202                 "# atomic up operation\n\t"
 203                 LOCK "incl %0\n\t"     /* ++sem->count */
 204                 "jle 2f\n"
 205                 "1:\n"
 206                 LOCK_SECTION_START("")
 207                 "2:\tcall __up_wakeup\n\t"
 208                 "jmp 1b\n"
 209                 LOCK_SECTION_END
 210                 ".subsection 0\n"
 211                 :"=m" (sem->count)
 212                 :"c" (sem)
 213                 :"memory");
 214 }
 215
 216 #endif
 217 #endif