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Diffstat (limited to 'include/asm-generic/mutex-dec.h')
-rw-r--r-- | include/asm-generic/mutex-dec.h | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h new file mode 100644 index 000000000000..40c6d1f86598 --- /dev/null +++ b/include/asm-generic/mutex-dec.h | |||
@@ -0,0 +1,110 @@ | |||
1 | /* | ||
2 | * 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 | #define __mutex_fastpath_lock(count, fail_fn) \ | ||
21 | do { \ | ||
22 | if (unlikely(atomic_dec_return(count) < 0)) \ | ||
23 | fail_fn(count); \ | ||
24 | else \ | ||
25 | smp_mb(); \ | ||
26 | } while (0) | ||
27 | |||
28 | /** | ||
29 | * __mutex_fastpath_lock_retval - try to take the lock by moving the count | ||
30 | * from 1 to a 0 value | ||
31 | * @count: pointer of type atomic_t | ||
32 | * @fail_fn: function to call if the original value was not 1 | ||
33 | * | ||
34 | * Change the count from 1 to a value lower than 1, and call <fail_fn> if | ||
35 | * it wasn't 1 originally. This function returns 0 if the fastpath succeeds, | ||
36 | * or anything the slow path function returns. | ||
37 | */ | ||
38 | static inline int | ||
39 | __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) | ||
40 | { | ||
41 | if (unlikely(atomic_dec_return(count) < 0)) | ||
42 | return fail_fn(count); | ||
43 | else { | ||
44 | smp_mb(); | ||
45 | return 0; | ||
46 | } | ||
47 | } | ||
48 | |||
49 | /** | ||
50 | * __mutex_fastpath_unlock - try to promote the count from 0 to 1 | ||
51 | * @count: pointer of type atomic_t | ||
52 | * @fail_fn: function to call if the original value was not 0 | ||
53 | * | ||
54 | * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>. | ||
55 | * In the failure case, this function is allowed to either set the value to | ||
56 | * 1, or to set it to a value lower than 1. | ||
57 | * | ||
58 | * If the implementation sets it to a value of lower than 1, then the | ||
59 | * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs | ||
60 | * to return 0 otherwise. | ||
61 | */ | ||
62 | #define __mutex_fastpath_unlock(count, fail_fn) \ | ||
63 | do { \ | ||
64 | smp_mb(); \ | ||
65 | if (unlikely(atomic_inc_return(count) <= 0)) \ | ||
66 | fail_fn(count); \ | ||
67 | } while (0) | ||
68 | |||
69 | #define __mutex_slowpath_needs_to_unlock() 1 | ||
70 | |||
71 | /** | ||
72 | * __mutex_fastpath_trylock - try to acquire the mutex, without waiting | ||
73 | * | ||
74 | * @count: pointer of type atomic_t | ||
75 | * @fail_fn: fallback function | ||
76 | * | ||
77 | * Change the count from 1 to a value lower than 1, and return 0 (failure) | ||
78 | * if it wasn't 1 originally, or return 1 (success) otherwise. This function | ||
79 | * MUST leave the value lower than 1 even when the "1" assertion wasn't true. | ||
80 | * Additionally, if the value was < 0 originally, this function must not leave | ||
81 | * it to 0 on failure. | ||
82 | * | ||
83 | * If the architecture has no effective trylock variant, it should call the | ||
84 | * <fail_fn> spinlock-based trylock variant unconditionally. | ||
85 | */ | ||
86 | static inline int | ||
87 | __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) | ||
88 | { | ||
89 | /* | ||
90 | * We have two variants here. The cmpxchg based one is the best one | ||
91 | * because it never induce a false contention state. It is included | ||
92 | * here because architectures using the inc/dec algorithms over the | ||
93 | * xchg ones are much more likely to support cmpxchg natively. | ||
94 | * | ||
95 | * If not we fall back to the spinlock based variant - that is | ||
96 | * just as efficient (and simpler) as a 'destructive' probing of | ||
97 | * the mutex state would be. | ||
98 | */ | ||
99 | #ifdef __HAVE_ARCH_CMPXCHG | ||
100 | if (likely(atomic_cmpxchg(count, 1, 0) == 1)) { | ||
101 | smp_mb(); | ||
102 | return 1; | ||
103 | } | ||
104 | return 0; | ||
105 | #else | ||
106 | return fail_fn(count); | ||
107 | #endif | ||
108 | } | ||
109 | |||
110 | #endif | ||