linux/include/asm-generic/mutex-dec.h
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   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(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 *  @fail_fn: function to call if the original value was not 1
  32 *
  33 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  34 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
  35 * or anything the slow path function returns.
  36 */
  37static inline int
  38__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
  39{
  40        if (unlikely(atomic_dec_return(count) < 0))
  41                return fail_fn(count);
  42        return 0;
  43}
  44
  45/**
  46 *  __mutex_fastpath_unlock - try to promote the count from 0 to 1
  47 *  @count: pointer of type atomic_t
  48 *  @fail_fn: function to call if the original value was not 0
  49 *
  50 * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
  51 * In the failure case, this function is allowed to either set the value to
  52 * 1, or to set it to a value lower than 1.
  53 *
  54 * If the implementation sets it to a value of lower than 1, then the
  55 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
  56 * to return 0 otherwise.
  57 */
  58static inline void
  59__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
  60{
  61        if (unlikely(atomic_inc_return(count) <= 0))
  62                fail_fn(count);
  63}
  64
  65#define __mutex_slowpath_needs_to_unlock()              1
  66
  67/**
  68 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  69 *
  70 *  @count: pointer of type atomic_t
  71 *  @fail_fn: fallback function
  72 *
  73 * Change the count from 1 to a value lower than 1, and return 0 (failure)
  74 * if it wasn't 1 originally, or return 1 (success) otherwise. This function
  75 * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
  76 * Additionally, if the value was < 0 originally, this function must not leave
  77 * it to 0 on failure.
  78 *
  79 * If the architecture has no effective trylock variant, it should call the
  80 * <fail_fn> spinlock-based trylock variant unconditionally.
  81 */
  82static inline int
  83__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
  84{
  85        if (likely(atomic_cmpxchg(count, 1, 0) == 1))
  86                return 1;
  87        return 0;
  88}
  89
  90#endif
  91
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