1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * Queue read/write lock
4 *
5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
6 *
7 * Authors: Waiman Long <waiman.long@hp.com>
8 */
9 #ifndef __ASM_GENERIC_QRWLOCK_H
10 #define __ASM_GENERIC_QRWLOCK_H
11
12 #include <linux/atomic.h>
13 #include <asm/barrier.h>
14 #include <asm/processor.h>
15
16 #include <asm-generic/qrwlock_types.h>
17
18 /* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
19
20 /*
21 * Writer states & reader shift and bias.
22 */
23 #define _QW_WAITING 0x100 /* A writer is waiting */
24 #define _QW_LOCKED 0x0ff /* A writer holds the lock */
25 #define _QW_WMASK 0x1ff /* Writer mask */
26 #define _QR_SHIFT 9 /* Reader count shift */
27 #define _QR_BIAS (1U << _QR_SHIFT)
28
29 /*
30 * External function declarations
31 */
32 extern void queued_read_lock_slowpath(struct qrwlock *lock);
33 extern void queued_write_lock_slowpath(struct qrwlock *lock);
34
35 /**
36 * queued_read_trylock - try to acquire read lock of a queue rwlock
37 * @lock : Pointer to queue rwlock structure
38 * Return: 1 if lock acquired, 0 if failed
39 */
queued_read_trylock(struct qrwlock * lock)40 static inline int queued_read_trylock(struct qrwlock *lock)
41 {
42 int cnts;
43
44 cnts = atomic_read(&lock->cnts);
45 if (likely(!(cnts & _QW_WMASK))) {
46 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
47 if (likely(!(cnts & _QW_WMASK)))
48 return 1;
49 atomic_sub(_QR_BIAS, &lock->cnts);
50 }
51 return 0;
52 }
53
54 /**
55 * queued_write_trylock - try to acquire write lock of a queue rwlock
56 * @lock : Pointer to queue rwlock structure
57 * Return: 1 if lock acquired, 0 if failed
58 */
queued_write_trylock(struct qrwlock * lock)59 static inline int queued_write_trylock(struct qrwlock *lock)
60 {
61 int cnts;
62
63 cnts = atomic_read(&lock->cnts);
64 if (unlikely(cnts))
65 return 0;
66
67 return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
68 _QW_LOCKED));
69 }
70 /**
71 * queued_read_lock - acquire read lock of a queue rwlock
72 * @lock: Pointer to queue rwlock structure
73 */
queued_read_lock(struct qrwlock * lock)74 static inline void queued_read_lock(struct qrwlock *lock)
75 {
76 int cnts;
77
78 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
79 if (likely(!(cnts & _QW_WMASK)))
80 return;
81
82 /* The slowpath will decrement the reader count, if necessary. */
83 queued_read_lock_slowpath(lock);
84 }
85
86 /**
87 * queued_write_lock - acquire write lock of a queue rwlock
88 * @lock : Pointer to queue rwlock structure
89 */
queued_write_lock(struct qrwlock * lock)90 static inline void queued_write_lock(struct qrwlock *lock)
91 {
92 int cnts = 0;
93 /* Optimize for the unfair lock case where the fair flag is 0. */
94 if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
95 return;
96
97 queued_write_lock_slowpath(lock);
98 }
99
100 /**
101 * queued_read_unlock - release read lock of a queue rwlock
102 * @lock : Pointer to queue rwlock structure
103 */
queued_read_unlock(struct qrwlock * lock)104 static inline void queued_read_unlock(struct qrwlock *lock)
105 {
106 /*
107 * Atomically decrement the reader count
108 */
109 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
110 }
111
112 /**
113 * queued_write_unlock - release write lock of a queue rwlock
114 * @lock : Pointer to queue rwlock structure
115 */
queued_write_unlock(struct qrwlock * lock)116 static inline void queued_write_unlock(struct qrwlock *lock)
117 {
118 smp_store_release(&lock->wlocked, 0);
119 }
120
121 /**
122 * queued_rwlock_is_contended - check if the lock is contended
123 * @lock : Pointer to queue rwlock structure
124 * Return: 1 if lock contended, 0 otherwise
125 */
queued_rwlock_is_contended(struct qrwlock * lock)126 static inline int queued_rwlock_is_contended(struct qrwlock *lock)
127 {
128 return arch_spin_is_locked(&lock->wait_lock);
129 }
130
131 /*
132 * Remapping rwlock architecture specific functions to the corresponding
133 * queue rwlock functions.
134 */
135 #define arch_read_lock(l) queued_read_lock(l)
136 #define arch_write_lock(l) queued_write_lock(l)
137 #define arch_read_trylock(l) queued_read_trylock(l)
138 #define arch_write_trylock(l) queued_write_trylock(l)
139 #define arch_read_unlock(l) queued_read_unlock(l)
140 #define arch_write_unlock(l) queued_write_unlock(l)
141 #define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
142
143 #endif /* __ASM_GENERIC_QRWLOCK_H */
144