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1 | /* |
2 | * Queued spinlock | |
3 | * | |
4 | * This program is free software; you can redistribute it and/or modify | |
5 | * it under the terms of the GNU General Public License as published by | |
6 | * the Free Software Foundation; either version 2 of the License, or | |
7 | * (at your option) any later version. | |
8 | * | |
9 | * This program is distributed in the hope that it will be useful, | |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | * GNU General Public License for more details. | |
13 | * | |
14 | * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. | |
15 | * | |
16 | * Authors: Waiman Long <waiman.long@hp.com> | |
17 | */ | |
18 | #ifndef __ASM_GENERIC_QSPINLOCK_H | |
19 | #define __ASM_GENERIC_QSPINLOCK_H | |
20 | ||
21 | #include <asm-generic/qspinlock_types.h> | |
22 | ||
23 | /** | |
24 | * queued_spin_is_locked - is the spinlock locked? | |
25 | * @lock: Pointer to queued spinlock structure | |
26 | * Return: 1 if it is locked, 0 otherwise | |
27 | */ | |
28 | static __always_inline int queued_spin_is_locked(struct qspinlock *lock) | |
29 | { | |
30 | return atomic_read(&lock->val); | |
31 | } | |
32 | ||
33 | /** | |
34 | * queued_spin_value_unlocked - is the spinlock structure unlocked? | |
35 | * @lock: queued spinlock structure | |
36 | * Return: 1 if it is unlocked, 0 otherwise | |
37 | * | |
38 | * N.B. Whenever there are tasks waiting for the lock, it is considered | |
39 | * locked wrt the lockref code to avoid lock stealing by the lockref | |
40 | * code and change things underneath the lock. This also allows some | |
41 | * optimizations to be applied without conflict with lockref. | |
42 | */ | |
43 | static __always_inline int queued_spin_value_unlocked(struct qspinlock lock) | |
44 | { | |
45 | return !atomic_read(&lock.val); | |
46 | } | |
47 | ||
48 | /** | |
49 | * queued_spin_is_contended - check if the lock is contended | |
50 | * @lock : Pointer to queued spinlock structure | |
51 | * Return: 1 if lock contended, 0 otherwise | |
52 | */ | |
53 | static __always_inline int queued_spin_is_contended(struct qspinlock *lock) | |
54 | { | |
55 | return atomic_read(&lock->val) & ~_Q_LOCKED_MASK; | |
56 | } | |
57 | /** | |
58 | * queued_spin_trylock - try to acquire the queued spinlock | |
59 | * @lock : Pointer to queued spinlock structure | |
60 | * Return: 1 if lock acquired, 0 if failed | |
61 | */ | |
62 | static __always_inline int queued_spin_trylock(struct qspinlock *lock) | |
63 | { | |
64 | if (!atomic_read(&lock->val) && | |
65 | (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0)) | |
66 | return 1; | |
67 | return 0; | |
68 | } | |
69 | ||
70 | extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); | |
71 | ||
72 | /** | |
73 | * queued_spin_lock - acquire a queued spinlock | |
74 | * @lock: Pointer to queued spinlock structure | |
75 | */ | |
76 | static __always_inline void queued_spin_lock(struct qspinlock *lock) | |
77 | { | |
78 | u32 val; | |
79 | ||
80 | val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL); | |
81 | if (likely(val == 0)) | |
82 | return; | |
83 | queued_spin_lock_slowpath(lock, val); | |
84 | } | |
85 | ||
86 | #ifndef queued_spin_unlock | |
87 | /** | |
88 | * queued_spin_unlock - release a queued spinlock | |
89 | * @lock : Pointer to queued spinlock structure | |
90 | */ | |
91 | static __always_inline void queued_spin_unlock(struct qspinlock *lock) | |
92 | { | |
93 | /* | |
94 | * smp_mb__before_atomic() in order to guarantee release semantics | |
95 | */ | |
96 | smp_mb__before_atomic_dec(); | |
97 | atomic_sub(_Q_LOCKED_VAL, &lock->val); | |
98 | } | |
99 | #endif | |
100 | ||
101 | /** | |
102 | * queued_spin_unlock_wait - wait until current lock holder releases the lock | |
103 | * @lock : Pointer to queued spinlock structure | |
104 | * | |
105 | * There is a very slight possibility of live-lock if the lockers keep coming | |
106 | * and the waiter is just unfortunate enough to not see any unlock state. | |
107 | */ | |
108 | static inline void queued_spin_unlock_wait(struct qspinlock *lock) | |
109 | { | |
110 | while (atomic_read(&lock->val) & _Q_LOCKED_MASK) | |
111 | cpu_relax(); | |
112 | } | |
113 | ||
114 | /* | |
115 | * Initializier | |
116 | */ | |
117 | #define __ARCH_SPIN_LOCK_UNLOCKED { ATOMIC_INIT(0) } | |
118 | ||
119 | /* | |
120 | * Remapping spinlock architecture specific functions to the corresponding | |
121 | * queued spinlock functions. | |
122 | */ | |
123 | #define arch_spin_is_locked(l) queued_spin_is_locked(l) | |
124 | #define arch_spin_is_contended(l) queued_spin_is_contended(l) | |
125 | #define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l) | |
126 | #define arch_spin_lock(l) queued_spin_lock(l) | |
127 | #define arch_spin_trylock(l) queued_spin_trylock(l) | |
128 | #define arch_spin_unlock(l) queued_spin_unlock(l) | |
129 | #define arch_spin_lock_flags(l, f) queued_spin_lock(l) | |
130 | #define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l) | |
131 | ||
132 | #endif /* __ASM_GENERIC_QSPINLOCK_H */ |