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Ingo Molnar620a6fd2006-01-09 15:59:17 -08001/*
Uwe Zeisbergerf30c2262006-10-03 23:01:26 +02002 * include/asm-generic/mutex-dec.h
Ingo Molnar620a6fd2006-01-09 15:59:17 -08003 *
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 */
Nicolas Pitree358c1a2006-03-31 02:32:13 -080020static inline void
Harvey Harrison144b2a92008-02-08 04:19:56 -080021__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
Nicolas Pitree358c1a2006-03-31 02:32:13 -080022{
23 if (unlikely(atomic_dec_return(count) < 0))
24 fail_fn(count);
Nicolas Pitree358c1a2006-03-31 02:32:13 -080025}
Ingo Molnar620a6fd2006-01-09 15:59:17 -080026
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
Ingo Molnar620a6fd2006-01-09 15:59:17 -080031 *
Maarten Lankhorsta41b56e2013-06-20 13:31:05 +020032 * Change the count from 1 to a value lower than 1. This function returns 0
33 * if the fastpath succeeds, or -1 otherwise.
Ingo Molnar620a6fd2006-01-09 15:59:17 -080034 */
35static inline int
Maarten Lankhorsta41b56e2013-06-20 13:31:05 +020036__mutex_fastpath_lock_retval(atomic_t *count)
Ingo Molnar620a6fd2006-01-09 15:59:17 -080037{
38 if (unlikely(atomic_dec_return(count) < 0))
Maarten Lankhorsta41b56e2013-06-20 13:31:05 +020039 return -1;
Nick Piggina8ddac72008-10-21 10:59:15 +020040 return 0;
Ingo Molnar620a6fd2006-01-09 15:59:17 -080041}
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 */
Nicolas Pitree358c1a2006-03-31 02:32:13 -080056static inline void
Harvey Harrison144b2a92008-02-08 04:19:56 -080057__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
Nicolas Pitree358c1a2006-03-31 02:32:13 -080058{
Nicolas Pitree358c1a2006-03-31 02:32:13 -080059 if (unlikely(atomic_inc_return(count) <= 0))
60 fail_fn(count);
61}
Ingo Molnar620a6fd2006-01-09 15:59:17 -080062
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 */
80static inline int
81__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
82{
Nick Piggina8ddac72008-10-21 10:59:15 +020083 if (likely(atomic_cmpxchg(count, 1, 0) == 1))
Ingo Molnar620a6fd2006-01-09 15:59:17 -080084 return 1;
Ingo Molnar620a6fd2006-01-09 15:59:17 -080085 return 0;
Ingo Molnar620a6fd2006-01-09 15:59:17 -080086}
87
88#endif