LXR linux/arch/x86/include/asm/mutex

   1/*
   2 * Assembly implementation of the mutex fastpath, based on atomic
   3 * decrement/increment.
   4 *
   5 * started by Ingo Molnar:
   6 *
   7 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   8 */
   9#ifndef _ASM_X86_MUTEX_64_H
  10#define _ASM_X86_MUTEX_64_H
  11
  12/**
  13 * __mutex_fastpath_lock - decrement and call function if negative
  14 * @v: pointer of type atomic_t
  15 * @fail_fn: function to call if the result is negative
  16 *
  17 * Atomically decrements @v and calls <fail_fn> if the result is negative.
  18 */
  19#define __mutex_fastpath_lock(v, fail_fn)                       \
  20do {                                                            \
  21        unsigned long dummy;                                    \
  22                                                                \
  23        typecheck(atomic_t *, v);                               \
  24        typecheck_fn(void (*)(atomic_t *), fail_fn);            \
  25                                                                \
  26        asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"            \
  27                     "   jns 1f         \n"                     \
  28                     "   call " #fail_fn "\n"                   \
  29                     "1:"                                       \
  30                     : "=D" (dummy)                             \
  31                     : "D" (v)                                  \
  32                     : "rax", "rsi", "rdx", "rcx",              \
  33                       "r8", "r9", "r10", "r11", "memory");     \
  34} while (0)
  35
  36/**
  37 *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  38 *                                 from 1 to a 0 value
  39 *  @count: pointer of type atomic_t
  40 *  @fail_fn: function to call if the original value was not 1
  41 *
  42 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  43 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
  44 * or anything the slow path function returns
  45 */
  46static inline int __mutex_fastpath_lock_retval(atomic_t *count,
  47                                               int (*fail_fn)(atomic_t *))
  48{
  49        if (unlikely(atomic_dec_return(count) < 0))
  50                return fail_fn(count);
  51        else
  52                return 0;
  53}
  54
  55/**
  56 * __mutex_fastpath_unlock - increment and call function if nonpositive
  57 * @v: pointer of type atomic_t
  58 * @fail_fn: function to call if the result is nonpositive
  59 *
  60 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
  61 */
  62#define __mutex_fastpath_unlock(v, fail_fn)                     \
  63do {                                                            \
  64        unsigned long dummy;                                    \
  65                                                                \
  66        typecheck(atomic_t *, v);                               \
  67        typecheck_fn(void (*)(atomic_t *), fail_fn);            \
  68                                                                \
  69        asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"            \
  70                     "   jg 1f\n"                               \
  71                     "   call " #fail_fn "\n"                   \
  72                     "1:"                                       \
  73                     : "=D" (dummy)                             \
  74                     : "D" (v)                                  \
  75                     : "rax", "rsi", "rdx", "rcx",              \
  76                       "r8", "r9", "r10", "r11", "memory");     \
  77} while (0)
  78
  79#define __mutex_slowpath_needs_to_unlock()      1
  80
  81/**
  82 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  83 *
  84 *  @count: pointer of type atomic_t
  85 *  @fail_fn: fallback function
  86 *
  87 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
  88 * if it wasn't 1 originally. [the fallback function is never used on
  89 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
  90 */
  91static inline int __mutex_fastpath_trylock(atomic_t *count,
  92                                           int (*fail_fn)(atomic_t *))
  93{
  94        if (likely(atomic_cmpxchg(count, 1, 0) == 1))
  95                return 1;
  96        else
  97                return 0;
  98}
  99
 100#endif /* _ASM_X86_MUTEX_64_H */
 101