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