1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
|
/*
* include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
* in lib/rwsem.c.
*/
#ifndef _ASM_SH_RWSEM_H
#define _ASM_SH_RWSEM_H
#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif
#ifdef __KERNEL__
#define RWSEM_UNLOCKED_VALUE 0x00000000
#define RWSEM_ACTIVE_BIAS 0x00000001
#define RWSEM_ACTIVE_MASK 0x0000ffff
#define RWSEM_WAITING_BIAS (-0x00010000)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
smp_wmb();
else
rwsem_down_read_failed(sem);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
int tmp;
while ((tmp = sem->count) >= 0) {
if (tmp == cmpxchg(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
smp_wmb();
return 1;
}
}
return 0;
}
/*
* lock for writing
*/
static inline void __down_write(struct rw_semaphore *sem)
{
int tmp;
tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count));
if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
smp_wmb();
else
rwsem_down_write_failed(sem);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
int tmp;
tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
smp_wmb();
return tmp == RWSEM_UNLOCKED_VALUE;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
int tmp;
smp_wmb();
tmp = atomic_dec_return((atomic_t *)(&sem->count));
if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
smp_wmb();
if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
(atomic_t *)(&sem->count)) < 0)
rwsem_wake(sem);
}
/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
atomic_add(delta, (atomic_t *)(&sem->count));
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
int tmp;
smp_wmb();
tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
if (tmp < 0)
rwsem_downgrade_wake(sem);
}
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
__down_write(sem);
}
/*
* implement exchange and add functionality
*/
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
smp_mb();
return atomic_add_return(delta, (atomic_t *)(&sem->count));
}
#endif /* __KERNEL__ */
#endif /* _ASM_SH_RWSEM_H */
|
