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Linux kernel mirror (for testing)
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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_GENERIC_RWSEM_H
3#define _ASM_GENERIC_RWSEM_H
4
5#ifndef _LINUX_RWSEM_H
6#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
7#endif
8
9#ifdef __KERNEL__
10
11/*
12 * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
13 * Adapted largely from include/asm-i386/rwsem.h
14 * by Paul Mackerras <paulus@samba.org>.
15 */
16
17/*
18 * the semaphore definition
19 */
20#ifdef CONFIG_64BIT
21# define RWSEM_ACTIVE_MASK 0xffffffffL
22#else
23# define RWSEM_ACTIVE_MASK 0x0000ffffL
24#endif
25
26#define RWSEM_UNLOCKED_VALUE 0x00000000L
27#define RWSEM_ACTIVE_BIAS 0x00000001L
28#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
29#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
30#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
31
32/*
33 * lock for reading
34 */
35static inline void __down_read(struct rw_semaphore *sem)
36{
37 if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
38 rwsem_down_read_failed(sem);
39}
40
41static inline int __down_read_killable(struct rw_semaphore *sem)
42{
43 if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0)) {
44 if (IS_ERR(rwsem_down_read_failed_killable(sem)))
45 return -EINTR;
46 }
47
48 return 0;
49}
50
51static inline int __down_read_trylock(struct rw_semaphore *sem)
52{
53 long tmp;
54
55 while ((tmp = atomic_long_read(&sem->count)) >= 0) {
56 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
57 tmp + RWSEM_ACTIVE_READ_BIAS)) {
58 return 1;
59 }
60 }
61 return 0;
62}
63
64/*
65 * lock for writing
66 */
67static inline void __down_write(struct rw_semaphore *sem)
68{
69 long tmp;
70
71 tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
72 &sem->count);
73 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
74 rwsem_down_write_failed(sem);
75}
76
77static inline int __down_write_killable(struct rw_semaphore *sem)
78{
79 long tmp;
80
81 tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
82 &sem->count);
83 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
84 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
85 return -EINTR;
86 return 0;
87}
88
89static inline int __down_write_trylock(struct rw_semaphore *sem)
90{
91 long tmp;
92
93 tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
94 RWSEM_ACTIVE_WRITE_BIAS);
95 return tmp == RWSEM_UNLOCKED_VALUE;
96}
97
98/*
99 * unlock after reading
100 */
101static inline void __up_read(struct rw_semaphore *sem)
102{
103 long tmp;
104
105 tmp = atomic_long_dec_return_release(&sem->count);
106 if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
107 rwsem_wake(sem);
108}
109
110/*
111 * unlock after writing
112 */
113static inline void __up_write(struct rw_semaphore *sem)
114{
115 if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
116 &sem->count) < 0))
117 rwsem_wake(sem);
118}
119
120/*
121 * downgrade write lock to read lock
122 */
123static inline void __downgrade_write(struct rw_semaphore *sem)
124{
125 long tmp;
126
127 /*
128 * When downgrading from exclusive to shared ownership,
129 * anything inside the write-locked region cannot leak
130 * into the read side. In contrast, anything in the
131 * read-locked region is ok to be re-ordered into the
132 * write side. As such, rely on RELEASE semantics.
133 */
134 tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
135 if (tmp < 0)
136 rwsem_downgrade_wake(sem);
137}
138
139#endif /* __KERNEL__ */
140#endif /* _ASM_GENERIC_RWSEM_H */