1/* 2 * Assembly implementation of the mutex fastpath, based on atomic 3 * decrement/increment. 4 * 5 * started by Ingo Molnar: 6 * 7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> 8 */ 9#ifndef _ASM_X86_MUTEX_32_H 10#define _ASM_X86_MUTEX_32_H 11 12#include <asm/alternative.h> 13 14/** 15 * __mutex_fastpath_lock - try to take the lock by moving the count 16 * from 1 to a 0 value 17 * @count: pointer of type atomic_t 18 * @fn: function to call if the original value was not 1 19 * 20 * Change the count from 1 to a value lower than 1, and call <fn> if it 21 * wasn't 1 originally. This function MUST leave the value lower than 1 22 * even when the "1" assertion wasn't true. 23 */ 24#define __mutex_fastpath_lock(count, fail_fn) \ 25do { \ 26 unsigned int dummy; \ 27 \ 28 typecheck(atomic_t *, count); \ 29 typecheck_fn(void (*)(atomic_t *), fail_fn); \ 30 \ 31 asm volatile(LOCK_PREFIX " decl (%%eax)\n" \ 32 " jns 1f \n" \ 33 " call " #fail_fn "\n" \ 34 "1:\n" \ 35 : "=a" (dummy) \ 36 : "a" (count) \ 37 : "memory", "ecx", "edx"); \ 38} while (0) 39 40 41/** 42 * __mutex_fastpath_lock_retval - try to take the lock by moving the count 43 * from 1 to a 0 value 44 * @count: pointer of type atomic_t 45 * 46 * Change the count from 1 to a value lower than 1. This function returns 0 47 * if the fastpath succeeds, or -1 otherwise. 48 */ 49static inline int __mutex_fastpath_lock_retval(atomic_t *count) 50{ 51 if (unlikely(atomic_dec_return(count) < 0)) 52 return -1; 53 else 54 return 0; 55} 56 57/** 58 * __mutex_fastpath_unlock - try to promote the mutex from 0 to 1 59 * @count: pointer of type atomic_t 60 * @fail_fn: function to call if the original value was not 0 61 * 62 * try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>. 63 * In the failure case, this function is allowed to either set the value 64 * to 1, or to set it to a value lower than 1. 65 * 66 * If the implementation sets it to a value of lower than 1, the 67 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs 68 * to return 0 otherwise. 69 */ 70#define __mutex_fastpath_unlock(count, fail_fn) \ 71do { \ 72 unsigned int dummy; \ 73 \ 74 typecheck(atomic_t *, count); \ 75 typecheck_fn(void (*)(atomic_t *), fail_fn); \ 76 \ 77 asm volatile(LOCK_PREFIX " incl (%%eax)\n" \ 78 " jg 1f\n" \ 79 " call " #fail_fn "\n" \ 80 "1:\n" \ 81 : "=a" (dummy) \ 82 : "a" (count) \ 83 : "memory", "ecx", "edx"); \ 84} while (0) 85 86#define __mutex_slowpath_needs_to_unlock() 1 87 88/** 89 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting 90 * 91 * @count: pointer of type atomic_t 92 * @fail_fn: fallback function 93 * 94 * Change the count from 1 to a value lower than 1, and return 0 (failure) 95 * if it wasn't 1 originally, or return 1 (success) otherwise. This function 96 * MUST leave the value lower than 1 even when the "1" assertion wasn't true. 97 * Additionally, if the value was < 0 originally, this function must not leave 98 * it to 0 on failure. 99 */ 100static inline int __mutex_fastpath_trylock(atomic_t *count, 101 int (*fail_fn)(atomic_t *)) 102{ 103 /* cmpxchg because it never induces a false contention state. */ 104 if (likely(atomic_cmpxchg(count, 1, 0) == 1)) 105 return 1; 106 107 return 0; 108} 109 110#endif /* _ASM_X86_MUTEX_32_H */ 111