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
|
// SPDX-License-Identifier: GPL-2.0
#include <linux/export.h>
#include <linux/lockref.h>
#if USE_CMPXCHG_LOCKREF
/*
* Note that the "cmpxchg()" reloads the "old" value for the
* failure case.
*/
#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
int retry = 100; \
struct lockref old; \
BUILD_BUG_ON(sizeof(old) != 8); \
old.lock_count = READ_ONCE(lockref->lock_count); \
while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
struct lockref new = old; \
CODE \
if (likely(try_cmpxchg64_relaxed(&lockref->lock_count, \
&old.lock_count, \
new.lock_count))) { \
SUCCESS; \
} \
if (!--retry) \
break; \
} \
} while (0)
#else
#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
#endif
/**
* lockref_get - Increments reference count unconditionally
* @lockref: pointer to lockref structure
*
* This operation is only valid if you already hold a reference
* to the object, so you know the count cannot be zero.
*/
void lockref_get(struct lockref *lockref)
{
CMPXCHG_LOOP(
new.count++;
,
return;
);
spin_lock(&lockref->lock);
lockref->count++;
spin_unlock(&lockref->lock);
}
EXPORT_SYMBOL(lockref_get);
/**
* lockref_get_not_zero - Increments count unless the count is 0 or dead
* @lockref: pointer to lockref structure
* Return: 1 if count updated successfully or 0 if count was zero
*/
bool lockref_get_not_zero(struct lockref *lockref)
{
bool retval = false;
CMPXCHG_LOOP(
new.count++;
if (old.count <= 0)
return false;
,
return true;
);
spin_lock(&lockref->lock);
if (lockref->count > 0) {
lockref->count++;
retval = true;
}
spin_unlock(&lockref->lock);
return retval;
}
EXPORT_SYMBOL(lockref_get_not_zero);
/**
* lockref_put_return - Decrement reference count if possible
* @lockref: pointer to lockref structure
*
* Decrement the reference count and return the new value.
* If the lockref was dead or locked, return -1.
*/
int lockref_put_return(struct lockref *lockref)
{
CMPXCHG_LOOP(
new.count--;
if (old.count <= 0)
return -1;
,
return new.count;
);
return -1;
}
EXPORT_SYMBOL(lockref_put_return);
/**
* lockref_put_or_lock - decrements count unless count <= 1 before decrement
* @lockref: pointer to lockref structure
* Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
*/
bool lockref_put_or_lock(struct lockref *lockref)
{
CMPXCHG_LOOP(
new.count--;
if (old.count <= 1)
break;
,
return true;
);
spin_lock(&lockref->lock);
if (lockref->count <= 1)
return false;
lockref->count--;
spin_unlock(&lockref->lock);
return true;
}
EXPORT_SYMBOL(lockref_put_or_lock);
/**
* lockref_mark_dead - mark lockref dead
* @lockref: pointer to lockref structure
*/
void lockref_mark_dead(struct lockref *lockref)
{
assert_spin_locked(&lockref->lock);
lockref->count = -128;
}
EXPORT_SYMBOL(lockref_mark_dead);
/**
* lockref_get_not_dead - Increments count unless the ref is dead
* @lockref: pointer to lockref structure
* Return: 1 if count updated successfully or 0 if lockref was dead
*/
bool lockref_get_not_dead(struct lockref *lockref)
{
bool retval = false;
CMPXCHG_LOOP(
new.count++;
if (old.count < 0)
return false;
,
return true;
);
spin_lock(&lockref->lock);
if (lockref->count >= 0) {
lockref->count++;
retval = true;
}
spin_unlock(&lockref->lock);
return retval;
}
EXPORT_SYMBOL(lockref_get_not_dead);
|
