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
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
|
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
#include <asm/barrier.h>
#include <asm/ldcw.h>
#include <asm/processor.h>
#include <asm/spinlock_types.h>
static inline int arch_spin_is_locked(arch_spinlock_t *x)
{
volatile unsigned int *a = __ldcw_align(x);
return *a == 0;
}
#define arch_spin_lock(lock) arch_spin_lock_flags(lock, 0)
static inline void arch_spin_lock_flags(arch_spinlock_t *x,
unsigned long flags)
{
volatile unsigned int *a;
mb();
a = __ldcw_align(x);
while (__ldcw(a) == 0)
while (*a == 0)
if (flags & PSW_SM_I) {
local_irq_enable();
cpu_relax();
local_irq_disable();
} else
cpu_relax();
mb();
}
static inline void arch_spin_unlock(arch_spinlock_t *x)
{
volatile unsigned int *a;
mb();
a = __ldcw_align(x);
*a = 1;
mb();
}
static inline int arch_spin_trylock(arch_spinlock_t *x)
{
volatile unsigned int *a;
int ret;
mb();
a = __ldcw_align(x);
ret = __ldcw(a) != 0;
mb();
return ret;
}
/*
* Read-write spinlocks, allowing multiple readers but only one writer.
* Linux rwlocks are unfair to writers; they can be starved for an indefinite
* time by readers. With care, they can also be taken in interrupt context.
*
* In the PA-RISC implementation, we have a spinlock and a counter.
* Readers use the lock to serialise their access to the counter (which
* records how many readers currently hold the lock).
* Writers hold the spinlock, preventing any readers or other writers from
* grabbing the rwlock.
*/
/* Note that we have to ensure interrupts are disabled in case we're
* interrupted by some other code that wants to grab the same read lock */
static __inline__ void arch_read_lock(arch_rwlock_t *rw)
{
unsigned long flags;
local_irq_save(flags);
arch_spin_lock_flags(&rw->lock, flags);
rw->counter++;
arch_spin_unlock(&rw->lock);
local_irq_restore(flags);
}
/* Note that we have to ensure interrupts are disabled in case we're
* interrupted by some other code that wants to grab the same read lock */
static __inline__ void arch_read_unlock(arch_rwlock_t *rw)
{
unsigned long flags;
local_irq_save(flags);
arch_spin_lock_flags(&rw->lock, flags);
rw->counter--;
arch_spin_unlock(&rw->lock);
local_irq_restore(flags);
}
/* Note that we have to ensure interrupts are disabled in case we're
* interrupted by some other code that wants to grab the same read lock */
static __inline__ int arch_read_trylock(arch_rwlock_t *rw)
{
unsigned long flags;
retry:
local_irq_save(flags);
if (arch_spin_trylock(&rw->lock)) {
rw->counter++;
arch_spin_unlock(&rw->lock);
local_irq_restore(flags);
return 1;
}
local_irq_restore(flags);
/* If write-locked, we fail to acquire the lock */
if (rw->counter < 0)
return 0;
/* Wait until we have a realistic chance at the lock */
while (arch_spin_is_locked(&rw->lock) && rw->counter >= 0)
cpu_relax();
goto retry;
}
/* Note that we have to ensure interrupts are disabled in case we're
* interrupted by some other code that wants to read_trylock() this lock */
static __inline__ void arch_write_lock(arch_rwlock_t *rw)
{
unsigned long flags;
retry:
local_irq_save(flags);
arch_spin_lock_flags(&rw->lock, flags);
if (rw->counter != 0) {
arch_spin_unlock(&rw->lock);
local_irq_restore(flags);
while (rw->counter != 0)
cpu_relax();
goto retry;
}
rw->counter = -1; /* mark as write-locked */
mb();
local_irq_restore(flags);
}
static __inline__ void arch_write_unlock(arch_rwlock_t *rw)
{
rw->counter = 0;
arch_spin_unlock(&rw->lock);
}
/* Note that we have to ensure interrupts are disabled in case we're
* interrupted by some other code that wants to read_trylock() this lock */
static __inline__ int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned long flags;
int result = 0;
local_irq_save(flags);
if (arch_spin_trylock(&rw->lock)) {
if (rw->counter == 0) {
rw->counter = -1;
result = 1;
} else {
/* Read-locked. Oh well. */
arch_spin_unlock(&rw->lock);
}
}
local_irq_restore(flags);
return result;
}
/*
* read_can_lock - would read_trylock() succeed?
* @lock: the rwlock in question.
*/
static __inline__ int arch_read_can_lock(arch_rwlock_t *rw)
{
return rw->counter >= 0;
}
/*
* write_can_lock - would write_trylock() succeed?
* @lock: the rwlock in question.
*/
static __inline__ int arch_write_can_lock(arch_rwlock_t *rw)
{
return !rw->counter;
}
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
#endif /* __ASM_SPINLOCK_H */
|
