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 */
__down_read(struct rw_semaphore * sem)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
__down_read_trylock(struct rw_semaphore * sem)41 static inline int __down_read_trylock(struct rw_semaphore *sem)
42 {
43 long tmp;
44
45 while ((tmp = atomic_long_read(&sem->count)) >= 0) {
46 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
47 tmp + RWSEM_ACTIVE_READ_BIAS)) {
48 return 1;
49 }
50 }
51 return 0;
52 }
53
54 /*
55 * lock for writing
56 */
__down_write(struct rw_semaphore * sem)57 static inline void __down_write(struct rw_semaphore *sem)
58 {
59 long tmp;
60
61 tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
62 &sem->count);
63 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
64 rwsem_down_write_failed(sem);
65 }
66
__down_write_killable(struct rw_semaphore * sem)67 static inline int __down_write_killable(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 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
75 return -EINTR;
76 return 0;
77 }
78
__down_write_trylock(struct rw_semaphore * sem)79 static inline int __down_write_trylock(struct rw_semaphore *sem)
80 {
81 long tmp;
82
83 tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
84 RWSEM_ACTIVE_WRITE_BIAS);
85 return tmp == RWSEM_UNLOCKED_VALUE;
86 }
87
88 /*
89 * unlock after reading
90 */
__up_read(struct rw_semaphore * sem)91 static inline void __up_read(struct rw_semaphore *sem)
92 {
93 long tmp;
94
95 tmp = atomic_long_dec_return_release(&sem->count);
96 if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
97 rwsem_wake(sem);
98 }
99
100 /*
101 * unlock after writing
102 */
__up_write(struct rw_semaphore * sem)103 static inline void __up_write(struct rw_semaphore *sem)
104 {
105 if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
106 &sem->count) < 0))
107 rwsem_wake(sem);
108 }
109
110 /*
111 * downgrade write lock to read lock
112 */
__downgrade_write(struct rw_semaphore * sem)113 static inline void __downgrade_write(struct rw_semaphore *sem)
114 {
115 long tmp;
116
117 /*
118 * When downgrading from exclusive to shared ownership,
119 * anything inside the write-locked region cannot leak
120 * into the read side. In contrast, anything in the
121 * read-locked region is ok to be re-ordered into the
122 * write side. As such, rely on RELEASE semantics.
123 */
124 tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
125 if (tmp < 0)
126 rwsem_downgrade_wake(sem);
127 }
128
129 #endif /* __KERNEL__ */
130 #endif /* _ASM_GENERIC_RWSEM_H */
131