LXR linux/include/asm-generic/mutex-dec.h

   1/*
   2 * include/asm-generic/mutex-dec.h
   3 *
   4 * Generic implementation of the mutex fastpath, based on atomic
   5 * decrement/increment.
   6 */
   7#ifndef _ASM_GENERIC_MUTEX_DEC_H
   8#define _ASM_GENERIC_MUTEX_DEC_H
   9
  10/**
  11 *  __mutex_fastpath_lock - try to take the lock by moving the count
  12 *                          from 1 to a 0 value
  13 *  @count: pointer of type atomic_t
  14 *  @fail_fn: function to call if the original value was not 1
  15 *
  16 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  17 * it wasn't 1 originally. This function MUST leave the value lower than
  18 * 1 even when the "1" assertion wasn't true.
  19 */
  20static inline void
  21__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
  22{
  23        if (unlikely(atomic_dec_return_acquire(count) < 0))
  24                fail_fn(count);
  25}
  26
  27/**
  28 *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  29 *                                 from 1 to a 0 value
  30 *  @count: pointer of type atomic_t
  31 *
  32 * Change the count from 1 to a value lower than 1. This function returns 0
  33 * if the fastpath succeeds, or -1 otherwise.
  34 */
  35static inline int
  36__mutex_fastpath_lock_retval(atomic_t *count)
  37{
  38        if (unlikely(atomic_dec_return_acquire(count) < 0))
  39                return -1;
  40        return 0;
  41}
  42
  43/**
  44 *  __mutex_fastpath_unlock - try to promote the count from 0 to 1
  45 *  @count: pointer of type atomic_t
  46 *  @fail_fn: function to call if the original value was not 0
  47 *
  48 * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
  49 * In the failure case, this function is allowed to either set the value to
  50 * 1, or to set it to a value lower than 1.
  51 *
  52 * If the implementation sets it to a value of lower than 1, then the
  53 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
  54 * to return 0 otherwise.
  55 */
  56static inline void
  57__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  58{
  59        if (unlikely(atomic_inc_return_release(count) <= 0))
  60                fail_fn(count);
  61}
  62
  63#define __mutex_slowpath_needs_to_unlock()              1
  64
  65/**
  66 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  67 *
  68 *  @count: pointer of type atomic_t
  69 *  @fail_fn: fallback function
  70 *
  71 * Change the count from 1 to a value lower than 1, and return 0 (failure)
  72 * if it wasn't 1 originally, or return 1 (success) otherwise. This function
  73 * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
  74 * Additionally, if the value was < 0 originally, this function must not leave
  75 * it to 0 on failure.
  76 *
  77 * If the architecture has no effective trylock variant, it should call the
  78 * <fail_fn> spinlock-based trylock variant unconditionally.
  79 */
  80static inline int
  81__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  82{
  83        if (likely(atomic_read(count) == 1 && atomic_cmpxchg_acquire(count, 1, 0) == 1))
  84                return 1;
  85        return 0;
  86}
  87
  88#endif
  89