include/asm-x86_64/mutex.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_MUTEX_H
  10 #define _ASM_MUTEX_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)                               \
  20 do {                                                                    \
  21         unsigned long dummy;                                            \
  22                                                                         \
  23         typecheck(atomic_t *, v);                                       \
  24         typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);           \
  25                                                                         \
  26         __asm__ __volatile__(                                           \
  27                 LOCK_PREFIX "   decl (%%rdi)    \n"                     \
  28                         "   js 2f               \n"                     \
  29                         "1:                     \n"                     \
  30                                                                         \
  31                 LOCK_SECTION_START("")                                  \
  32                         "2: call "#fail_fn"     \n"                     \
  33                         "   jmp 1b              \n"                     \
  34                 LOCK_SECTION_END                                        \
  35                                                                         \
  36                 :"=D" (dummy)                                           \
  37                 : "D" (v)                                               \
  38                 : "rax", "rsi", "rdx", "rcx",                           \
  39                   "r8", "r9", "r10", "r11", "memory");                  \
  40 } while (0)
  41
  42 /**
  43  *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  44  *                                 from 1 to a 0 value
  45  *  @count: pointer of type atomic_t
  46  *  @fail_fn: function to call if the original value was not 1
  47  *
  48  * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  49  * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
  50  * or anything the slow path function returns
  51  */
  52 static inline int
  53 __mutex_fastpath_lock_retval(atomic_t *count,
  54                              int fastcall (*fail_fn)(atomic_t *))
  55 {
  56         if (unlikely(atomic_dec_return(count) < 0))
  57                 return fail_fn(count);
  58         else
  59                 return 0;
  60 }
  61
  62 /**
  63  * __mutex_fastpath_unlock - increment and call function if nonpositive
  64  * @v: pointer of type atomic_t
  65  * @fail_fn: function to call if the result is nonpositive
  66  *
  67  * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
  68  */
  69 #define __mutex_fastpath_unlock(v, fail_fn)                             \
  70 do {                                                                    \
  71         unsigned long dummy;                                            \
  72                                                                         \
  73         typecheck(atomic_t *, v);                                       \
  74         typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);           \
  75                                                                         \
  76         __asm__ __volatile__(                                           \
  77                 LOCK_PREFIX "   incl (%%rdi)    \n"                     \
  78                         "   jle 2f              \n"                     \
  79                         "1:                     \n"                     \
  80                                                                         \
  81                 LOCK_SECTION_START("")                                  \
  82                         "2: call "#fail_fn"     \n"                     \
  83                         "   jmp 1b              \n"                     \
  84                 LOCK_SECTION_END                                        \
  85                                                                         \
  86                 :"=D" (dummy)                                           \
  87                 : "D" (v)                                               \
  88                 : "rax", "rsi", "rdx", "rcx",                           \
  89                   "r8", "r9", "r10", "r11", "memory");                  \
  90 } while (0)
  91
  92 #define __mutex_slowpath_needs_to_unlock()      1
  93
  94 /**
  95  * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  96  *
  97  *  @count: pointer of type atomic_t
  98  *  @fail_fn: fallback function
  99  *
 100  * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
 101  * if it wasn't 1 originally. [the fallback function is never used on
 102  * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
 103  */
 104 static inline int
 105 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
 106 {
 107         if (likely(atomic_cmpxchg(count, 1, 0) == 1))
 108                 return 1;
 109         else
 110                 return 0;
 111 }
 112
 113 #endif