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 *
  41 * Change the count from 1 to a value lower than 1. This function returns 0
  42 * if the fastpath succeeds, or -1 otherwise.
  43 */
  44static inline int __mutex_fastpath_lock_retval(atomic_t *count)
  45{
  46        if (unlikely(atomic_dec_return(count) < 0))
  47                return -1;
  48        else
  49                return 0;
  50}
  51
  52/**
  53 * __mutex_fastpath_unlock - increment and call function if nonpositive
  54 * @v: pointer of type atomic_t
  55 * @fail_fn: function to call if the result is nonpositive
  56 *
  57 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
  58 */
  59#define __mutex_fastpath_unlock(v, fail_fn)                     \
  60do {                                                            \
  61        unsigned long dummy;                                    \
  62                                                                \
  63        typecheck(atomic_t *, v);                               \
  64        typecheck_fn(void (*)(atomic_t *), fail_fn);            \
  65                                                                \
  66        asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"            \
  67                     "   jg 1f\n"                               \
  68                     "   call " #fail_fn "\n"                   \
  69                     "1:"                                       \
  70                     : "=D" (dummy)                             \
  71                     : "D" (v)                                  \
  72                     : "rax", "rsi", "rdx", "rcx",              \
  73                       "r8", "r9", "r10", "r11", "memory");     \
  74} while (0)
  75
  76#define __mutex_slowpath_needs_to_unlock()      1
  77
  78/**
  79 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  80 *
  81 *  @count: pointer of type atomic_t
  82 *  @fail_fn: fallback function
  83 *
  84 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
  85 * if it wasn't 1 originally. [the fallback function is never used on
  86 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
  87 */
  88static inline int __mutex_fastpath_trylock(atomic_t *count,
  89                                           int (*fail_fn)(atomic_t *))
  90{
  91        if (likely(atomic_cmpxchg(count, 1, 0) == 1))
  92                return 1;
  93        else
  94                return 0;
  95}
  96
  97#endif /* _ASM_X86_MUTEX_64_H */
  98