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  */
  20 static 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  */
  35 static 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  */
  56 static 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  */
  80 static 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