include/asm-x86_64/semaphore.h

   1 #ifndef _X86_64_SEMAPHORE_H
   2 #define _X86_64_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 <asm/rwlock.h>
  42 #include <linux/wait.h>
  43 #include <linux/rwsem.h>
  44 #include <linux/stringify.h>
  45
  46 struct semaphore {
  47         atomic_t count;
  48         int sleepers;
  49         wait_queue_head_t wait;
  50 };
  51
  52 #define __SEMAPHORE_INITIALIZER(name, n)                                \
  53 {                                                                       \
  54         .count          = ATOMIC_INIT(n),                               \
  55         .sleepers       = 0,                                            \
  56         .wait           = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait)    \
  57 }
  58
  59 #define __MUTEX_INITIALIZER(name) \
  60         __SEMAPHORE_INITIALIZER(name,1)
  61
  62 #define __DECLARE_SEMAPHORE_GENERIC(name,count) \
  63         struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
  64
  65 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
  66 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
  67
  68 static inline void sema_init (struct semaphore *sem, int val)
  69 {
  70 /*
  71  *      *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
  72  *
  73  * i'd rather use the more flexible initialization above, but sadly
  74  * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
  75  */
  76         atomic_set(&sem->count, val);
  77         sem->sleepers = 0;
  78         init_waitqueue_head(&sem->wait);
  79 }
  80
  81 static inline void init_MUTEX (struct semaphore *sem)
  82 {
  83         sema_init(sem, 1);
  84 }
  85
  86 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
  87 {
  88         sema_init(sem, 0);
  89 }
  90
  91 asmlinkage void __down_failed(void /* special register calling convention */);
  92 asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
  93 asmlinkage int  __down_failed_trylock(void  /* params in registers */);
  94 asmlinkage void __up_wakeup(void /* special register calling convention */);
  95
  96 asmlinkage void __down(struct semaphore * sem);
  97 asmlinkage int  __down_interruptible(struct semaphore * sem);
  98 asmlinkage int  __down_trylock(struct semaphore * sem);
  99 asmlinkage void __up(struct semaphore * sem);
 100
 101 /*
 102  * This is ugly, but we want the default case to fall through.
 103  * "__down_failed" is a special asm handler that calls the C
 104  * routine that actually waits. See arch/x86_64/kernel/semaphore.c
 105  */
 106 static inline void down(struct semaphore * sem)
 107 {
 108         might_sleep();
 109
 110         __asm__ __volatile__(
 111                 "# atomic down operation\n\t"
 112                 LOCK "decl %0\n\t"     /* --sem->count */
 113                 "js 2f\n"
 114                 "1:\n"
 115                 LOCK_SECTION_START("")
 116                 "2:\tcall __down_failed\n\t"
 117                 "jmp 1b\n"
 118                 LOCK_SECTION_END
 119                 :"=m" (sem->count)
 120                 :"D" (sem)
 121                 :"memory");
 122 }
 123
 124 /*
 125  * Interruptible try to acquire a semaphore.  If we obtained
 126  * it, return zero.  If we were interrupted, returns -EINTR
 127  */
 128 static inline int down_interruptible(struct semaphore * sem)
 129 {
 130         int result;
 131
 132         might_sleep();
 133
 134         __asm__ __volatile__(
 135                 "# atomic interruptible down operation\n\t"
 136                 LOCK "decl %1\n\t"     /* --sem->count */
 137                 "js 2f\n\t"
 138                 "xorl %0,%0\n"
 139                 "1:\n"
 140                 LOCK_SECTION_START("")
 141                 "2:\tcall __down_failed_interruptible\n\t"
 142                 "jmp 1b\n"
 143                 LOCK_SECTION_END
 144                 :"=a" (result), "=m" (sem->count)
 145                 :"D" (sem)
 146                 :"memory");
 147         return result;
 148 }
 149
 150 /*
 151  * Non-blockingly attempt to down() a semaphore.
 152  * Returns zero if we acquired it
 153  */
 154 static inline int down_trylock(struct semaphore * sem)
 155 {
 156         int result;
 157
 158         __asm__ __volatile__(
 159                 "# atomic interruptible down operation\n\t"
 160                 LOCK "decl %1\n\t"     /* --sem->count */
 161                 "js 2f\n\t"
 162                 "xorl %0,%0\n"
 163                 "1:\n"
 164                 LOCK_SECTION_START("")
 165                 "2:\tcall __down_failed_trylock\n\t"
 166                 "jmp 1b\n"
 167                 LOCK_SECTION_END
 168                 :"=a" (result), "=m" (sem->count)
 169                 :"D" (sem)
 170                 :"memory","cc");
 171         return result;
 172 }
 173
 174 /*
 175  * Note! This is subtle. We jump to wake people up only if
 176  * the semaphore was negative (== somebody was waiting on it).
 177  * The default case (no contention) will result in NO
 178  * jumps for both down() and up().
 179  */
 180 static inline void up(struct semaphore * sem)
 181 {
 182         __asm__ __volatile__(
 183                 "# atomic up operation\n\t"
 184                 LOCK "incl %0\n\t"     /* ++sem->count */
 185                 "jle 2f\n"
 186                 "1:\n"
 187                 LOCK_SECTION_START("")
 188                 "2:\tcall __up_wakeup\n\t"
 189                 "jmp 1b\n"
 190                 LOCK_SECTION_END
 191                 :"=m" (sem->count)
 192                 :"D" (sem)
 193                 :"memory");
 194 }
 195 #endif /* __KERNEL__ */
 196 #endif