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