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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 | */ | |
35 | static 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 | ||
41 | static 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 | ||
51 | static 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 | */ | |
67 | static 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 | ||
77 | static 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 | ||
89 | static 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 | */ | |
101 | static 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 | */ | |
113 | static 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 | */ | |
123 | static 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 */ |