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 __DECLARE_SEMAPHORE_GENERIC(name,count) \
  60         struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
  61
  62 #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
  63 #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
  64
  65 static inline void sema_init (struct semaphore *sem, int val)
  66 {
  67 /*
  68  *      *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
  69  *
  70  * i'd rather use the more flexible initialization above, but sadly
  71  * GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
  72  */
  73         atomic_set(&sem->count, val);
  74         sem->sleepers = 0;
  75         init_waitqueue_head(&sem->wait);
  76 }
  77
  78 static inline void init_MUTEX (struct semaphore *sem)
  79 {
  80         sema_init(sem, 1);
  81 }
  82
  83 static inline void init_MUTEX_LOCKED (struct semaphore *sem)
  84 {
  85         sema_init(sem, 0);
  86 }
  87
  88 asmlinkage void __down_failed(void /* special register calling convention */);
  89 asmlinkage int  __down_failed_interruptible(void  /* params in registers */);
  90 asmlinkage int  __down_failed_trylock(void  /* params in registers */);
  91 asmlinkage void __up_wakeup(void /* special register calling convention */);
  92
  93 asmlinkage void __down(struct semaphore * sem);
  94 asmlinkage int  __down_interruptible(struct semaphore * sem);
  95 asmlinkage int  __down_trylock(struct semaphore * sem);
  96 asmlinkage void __up(struct semaphore * sem);
  97
  98 /*
  99  * This is ugly, but we want the default case to fall through.
 100  * "__down_failed" is a special asm handler that calls the C
 101  * routine that actually waits. See arch/x86_64/kernel/semaphore.c
 102  */
 103 static inline void down(struct semaphore * sem)
 104 {
 105         might_sleep();
 106
 107         __asm__ __volatile__(
 108                 "# atomic down operation\n\t"
 109                 LOCK_PREFIX "decl %0\n\t"     /* --sem->count */
 110                 "jns 1f\n\t"
 111                 "call __down_failed\n"
 112                 "1:"
 113                 :"=m" (sem->count)
 114                 :"D" (sem)
 115                 :"memory");
 116 }
 117
 118 /*
 119  * Interruptible try to acquire a semaphore.  If we obtained
 120  * it, return zero.  If we were interrupted, returns -EINTR
 121  */
 122 static inline int down_interruptible(struct semaphore * sem)
 123 {
 124         int result;
 125
 126         might_sleep();
 127
 128         __asm__ __volatile__(
 129                 "# atomic interruptible down operation\n\t"
 130                 "xorl %0,%0\n\t"
 131                 LOCK_PREFIX "decl %1\n\t"     /* --sem->count */
 132                 "jns 2f\n\t"
 133                 "call __down_failed_interruptible\n"
 134                 "2:\n"
 135                 :"=&a" (result), "=m" (sem->count)
 136                 :"D" (sem)
 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                 "xorl %0,%0\n\t"
 152                 LOCK_PREFIX "decl %1\n\t"     /* --sem->count */
 153                 "jns 2f\n\t"
 154                 "call __down_failed_trylock\n\t"
 155                 "2:\n"
 156                 :"=&a" (result), "=m" (sem->count)
 157                 :"D" (sem)
 158                 :"memory","cc");
 159         return result;
 160 }
 161
 162 /*
 163  * Note! This is subtle. We jump to wake people up only if
 164  * the semaphore was negative (== somebody was waiting on it).
 165  * The default case (no contention) will result in NO
 166  * jumps for both down() and up().
 167  */
 168 static inline void up(struct semaphore * sem)
 169 {
 170         __asm__ __volatile__(
 171                 "# atomic up operation\n\t"
 172                 LOCK_PREFIX "incl %0\n\t"     /* ++sem->count */
 173                 "jg 1f\n\t"
 174                 "call __up_wakeup\n"
 175                 "1:"
 176                 :"=m" (sem->count)
 177                 :"D" (sem)
 178                 :"memory");
 179 }
 180 #endif /* __KERNEL__ */
 181 #endif