blob: 250a4acddb2b8975a6c8278a3c5b1d803f36b585 (
plain)
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
|
#ifndef _LINUX_PERCPU_RWSEM_H
#define _LINUX_PERCPU_RWSEM_H
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/delay.h>
struct percpu_rw_semaphore {
unsigned __percpu *counters;
bool locked;
struct mutex mtx;
};
#define light_mb() barrier()
#define heavy_mb() synchronize_sched()
static inline void percpu_down_read(struct percpu_rw_semaphore *p)
{
rcu_read_lock_sched();
if (unlikely(p->locked)) {
rcu_read_unlock_sched();
mutex_lock(&p->mtx);
this_cpu_inc(*p->counters);
mutex_unlock(&p->mtx);
return;
}
this_cpu_inc(*p->counters);
rcu_read_unlock_sched();
light_mb(); /* A, between read of p->locked and read of data, paired with D */
}
static inline void percpu_up_read(struct percpu_rw_semaphore *p)
{
light_mb(); /* B, between read of the data and write to p->counter, paired with C */
this_cpu_dec(*p->counters);
}
static inline unsigned __percpu_count(unsigned __percpu *counters)
{
unsigned total = 0;
int cpu;
for_each_possible_cpu(cpu)
total += ACCESS_ONCE(*per_cpu_ptr(counters, cpu));
return total;
}
static inline void percpu_down_write(struct percpu_rw_semaphore *p)
{
mutex_lock(&p->mtx);
p->locked = true;
synchronize_sched(); /* make sure that all readers exit the rcu_read_lock_sched region */
while (__percpu_count(p->counters))
msleep(1);
heavy_mb(); /* C, between read of p->counter and write to data, paired with B */
}
static inline void percpu_up_write(struct percpu_rw_semaphore *p)
{
heavy_mb(); /* D, between write to data and write to p->locked, paired with A */
p->locked = false;
mutex_unlock(&p->mtx);
}
static inline int percpu_init_rwsem(struct percpu_rw_semaphore *p)
{
p->counters = alloc_percpu(unsigned);
if (unlikely(!p->counters))
return -ENOMEM;
p->locked = false;
mutex_init(&p->mtx);
return 0;
}
static inline void percpu_free_rwsem(struct percpu_rw_semaphore *p)
{
free_percpu(p->counters);
p->counters = NULL; /* catch use after free bugs */
}
#endif
|
