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-rw-r--r--include/asm-generic/mutex-dec.h110
-rw-r--r--include/asm-generic/mutex-null.h24
-rw-r--r--include/asm-generic/mutex-xchg.h117
3 files changed, 251 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..74b18cda169f
--- /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) \
21do { \
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 */
38static 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) \
63do { \
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 */
86static 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
diff --git a/include/asm-generic/mutex-null.h b/include/asm-generic/mutex-null.h
new file mode 100644
index 000000000000..5cf8b7ce0c45
--- /dev/null
+++ b/include/asm-generic/mutex-null.h
@@ -0,0 +1,24 @@
1/*
2 * asm-generic/mutex-null.h
3 *
4 * Generic implementation of the mutex fastpath, based on NOP :-)
5 *
6 * This is used by the mutex-debugging infrastructure, but it can also
7 * be used by architectures that (for whatever reason) want to use the
8 * spinlock based slowpath.
9 */
10#ifndef _ASM_GENERIC_MUTEX_NULL_H
11#define _ASM_GENERIC_MUTEX_NULL_H
12
13/* extra parameter only needed for mutex debugging: */
14#ifndef __IP__
15# define __IP__
16#endif
17
18#define __mutex_fastpath_lock(count, fail_fn) fail_fn(count __RET_IP__)
19#define __mutex_fastpath_lock_retval(count, fail_fn) fail_fn(count __RET_IP__)
20#define __mutex_fastpath_unlock(count, fail_fn) fail_fn(count __RET_IP__)
21#define __mutex_fastpath_trylock(count, fail_fn) fail_fn(count)
22#define __mutex_slowpath_needs_to_unlock() 1
23
24#endif
diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
new file mode 100644
index 000000000000..1d24f47e6c48
--- /dev/null
+++ b/include/asm-generic/mutex-xchg.h
@@ -0,0 +1,117 @@
1/*
2 * asm-generic/mutex-xchg.h
3 *
4 * Generic implementation of the mutex fastpath, based on xchg().
5 *
6 * NOTE: An xchg based implementation is less optimal than an atomic
7 * decrement/increment based implementation. If your architecture
8 * has a reasonable atomic dec/inc then you should probably use
9 * asm-generic/mutex-dec.h instead, or you could open-code an
10 * optimized version in asm/mutex.h.
11 */
12#ifndef _ASM_GENERIC_MUTEX_XCHG_H
13#define _ASM_GENERIC_MUTEX_XCHG_H
14
15/**
16 * __mutex_fastpath_lock - try to take the lock by moving the count
17 * from 1 to a 0 value
18 * @count: pointer of type atomic_t
19 * @fail_fn: function to call if the original value was not 1
20 *
21 * Change the count from 1 to a value lower than 1, and call <fail_fn> if it
22 * wasn't 1 originally. This function MUST leave the value lower than 1
23 * even when the "1" assertion wasn't true.
24 */
25#define __mutex_fastpath_lock(count, fail_fn) \
26do { \
27 if (unlikely(atomic_xchg(count, 0) != 1)) \
28 fail_fn(count); \
29 else \
30 smp_mb(); \
31} while (0)
32
33
34/**
35 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
36 * from 1 to a 0 value
37 * @count: pointer of type atomic_t
38 * @fail_fn: function to call if the original value was not 1
39 *
40 * Change the count from 1 to a value lower than 1, and call <fail_fn> if it
41 * wasn't 1 originally. This function returns 0 if the fastpath succeeds,
42 * or anything the slow path function returns
43 */
44static inline int
45__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
46{
47 if (unlikely(atomic_xchg(count, 0) != 1))
48 return fail_fn(count);
49 else {
50 smp_mb();
51 return 0;
52 }
53}
54
55/**
56 * __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
57 * @count: pointer of type atomic_t
58 * @fail_fn: function to call if the original value was not 0
59 *
60 * try to promote the mutex from 0 to 1. if it wasn't 0, call <function>
61 * In the failure case, this function is allowed to either set the value to
62 * 1, or to set it to a value lower than one.
63 * If the implementation sets it to a value of lower than one, the
64 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
65 * to return 0 otherwise.
66 */
67#define __mutex_fastpath_unlock(count, fail_fn) \
68do { \
69 smp_mb(); \
70 if (unlikely(atomic_xchg(count, 1) != 0)) \
71 fail_fn(count); \
72} while (0)
73
74#define __mutex_slowpath_needs_to_unlock() 0
75
76/**
77 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
78 *
79 * @count: pointer of type atomic_t
80 * @fail_fn: spinlock based trylock implementation
81 *
82 * Change the count from 1 to a value lower than 1, and return 0 (failure)
83 * if it wasn't 1 originally, or return 1 (success) otherwise. This function
84 * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
85 * Additionally, if the value was < 0 originally, this function must not leave
86 * it to 0 on failure.
87 *
88 * If the architecture has no effective trylock variant, it should call the
89 * <fail_fn> spinlock-based trylock variant unconditionally.
90 */
91static inline int
92__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
93{
94 int prev = atomic_xchg(count, 0);
95
96 if (unlikely(prev < 0)) {
97 /*
98 * The lock was marked contended so we must restore that
99 * state. If while doing so we get back a prev value of 1
100 * then we just own it.
101 *
102 * [ In the rare case of the mutex going to 1, to 0, to -1
103 * and then back to 0 in this few-instructions window,
104 * this has the potential to trigger the slowpath for the
105 * owner's unlock path needlessly, but that's not a problem
106 * in practice. ]
107 */
108 prev = atomic_xchg(count, prev);
109 if (prev < 0)
110 prev = 0;
111 }
112 smp_mb();
113
114 return prev;
115}
116
117#endif
generated by cgit v1.2.2 (git 2.25.0) at 2025-11-01 09:42:30 -0400