arch/x86/include/asm/mutex_64.h

   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 #ifdef CC_HAVE_ASM_GOTO
  20 static inline void __mutex_fastpath_lock(atomic_t *v,
  21                                          void (*fail_fn)(atomic_t *))
  22 {
  23         asm_volatile_goto(LOCK_PREFIX "   decl %0\n"
  24                           "   jns %l[exit]\n"
  25                           : : "m" (v->counter)
  26                           : "memory", "cc"
  27                           : exit);
  28         fail_fn(v);
  29 exit:
  30         return;
  31 }
  32 #else
  33 #define __mutex_fastpath_lock(v, fail_fn)                       \
  34 do {                                                            \
  35         unsigned long dummy;                                    \
  36                                                                 \
  37         typecheck(atomic_t *, v);                               \
  38         typecheck_fn(void (*)(atomic_t *), fail_fn);            \
  39                                                                 \
  40         asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"            \
  41                      "   jns 1f         \n"                     \
  42                      "   call " #fail_fn "\n"                   \
  43                      "1:"                                       \
  44                      : "=D" (dummy)                             \
  45                      : "D" (v)                                  \
  46                      : "rax", "rsi", "rdx", "rcx",              \
  47                        "r8", "r9", "r10", "r11", "memory");     \
  48 } while (0)
  49 #endif
  50
  51 /**
  52  *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  53  *                                 from 1 to a 0 value
  54  *  @count: pointer of type atomic_t
  55  *
  56  * Change the count from 1 to a value lower than 1. This function returns 0
  57  * if the fastpath succeeds, or -1 otherwise.
  58  */
  59 static inline int __mutex_fastpath_lock_retval(atomic_t *count)
  60 {
  61         if (unlikely(atomic_dec_return(count) < 0))
  62                 return -1;
  63         else
  64                 return 0;
  65 }
  66
  67 /**
  68  * __mutex_fastpath_unlock - increment and call function if nonpositive
  69  * @v: pointer of type atomic_t
  70  * @fail_fn: function to call if the result is nonpositive
  71  *
  72  * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
  73  */
  74 #ifdef CC_HAVE_ASM_GOTO
  75 static inline void __mutex_fastpath_unlock(atomic_t *v,
  76                                            void (*fail_fn)(atomic_t *))
  77 {
  78         asm_volatile_goto(LOCK_PREFIX "   incl %0\n"
  79                           "   jg %l[exit]\n"
  80                           : : "m" (v->counter)
  81                           : "memory", "cc"
  82                           : exit);
  83         fail_fn(v);
  84 exit:
  85         return;
  86 }
  87 #else
  88 #define __mutex_fastpath_unlock(v, fail_fn)                     \
  89 do {                                                            \
  90         unsigned long dummy;                                    \
  91                                                                 \
  92         typecheck(atomic_t *, v);                               \
  93         typecheck_fn(void (*)(atomic_t *), fail_fn);            \
  94                                                                 \
  95         asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"            \
  96                      "   jg 1f\n"                               \
  97                      "   call " #fail_fn "\n"                   \
  98                      "1:"                                       \
  99                      : "=D" (dummy)                             \
 100                      : "D" (v)                                  \
 101                      : "rax", "rsi", "rdx", "rcx",              \
 102                        "r8", "r9", "r10", "r11", "memory");     \
 103 } while (0)
 104 #endif
 105
 106 #define __mutex_slowpath_needs_to_unlock()      1
 107
 108 /**
 109  * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
 110  *
 111  *  @count: pointer of type atomic_t
 112  *  @fail_fn: fallback function
 113  *
 114  * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
 115  * if it wasn't 1 originally. [the fallback function is never used on
 116  * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
 117  */
 118 static inline int __mutex_fastpath_trylock(atomic_t *count,
 119                                            int (*fail_fn)(atomic_t *))
 120 {
 121         if (likely(atomic_read(count) == 1 && atomic_cmpxchg(count, 1, 0) == 1))
 122                 return 1;
 123
 124         return 0;
 125 }
 126
 127 #endif /* _ASM_X86_MUTEX_64_H */