Root/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 */
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

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