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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                 :            :  */
      20                 :            : static inline void
      21                 :            : __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
      22                 :            : {
      23         [ +  + ]:   41055625 :         if (unlikely(atomic_dec_return(count) < 0))
      24                 :     657242 :                 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 [ #  # ][ #  # ]:    2292322 :         if (unlikely(atomic_dec_return(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   [ #  #  +  + ]:   42348465 :         if (unlikely(atomic_inc_return(count) <= 0))
      60                 :     636856 :                 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         [ +  + ]:     141693 :         if (likely(atomic_cmpxchg(count, 1, 0) == 1))
      84                 :            :                 return 1;
      85                 :            :         return 0;
      86                 :            : }
      87                 :            : 
      88                 :            : #endif