Root/lib/lockref.c

1#include <linux/export.h>
2#include <linux/lockref.h>
3#include <linux/mutex.h>
4
5#if USE_CMPXCHG_LOCKREF
6
7/*
8 * Allow weakly-ordered memory architectures to provide barrier-less
9 * cmpxchg semantics for lockref updates.
10 */
11#ifndef cmpxchg64_relaxed
12# define cmpxchg64_relaxed cmpxchg64
13#endif
14
15/*
16 * Note that the "cmpxchg()" reloads the "old" value for the
17 * failure case.
18 */
19#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
20    struct lockref old; \
21    BUILD_BUG_ON(sizeof(old) != 8); \
22    old.lock_count = ACCESS_ONCE(lockref->lock_count); \
23    while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
24        struct lockref new = old, prev = old; \
25        CODE \
26        old.lock_count = cmpxchg64_relaxed(&lockref->lock_count, \
27                           old.lock_count, \
28                           new.lock_count); \
29        if (likely(old.lock_count == prev.lock_count)) { \
30            SUCCESS; \
31        } \
32        arch_mutex_cpu_relax(); \
33    } \
34} while (0)
35
36#else
37
38#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
39
40#endif
41
42/**
43 * lockref_get - Increments reference count unconditionally
44 * @lockref: pointer to lockref structure
45 *
46 * This operation is only valid if you already hold a reference
47 * to the object, so you know the count cannot be zero.
48 */
49void lockref_get(struct lockref *lockref)
50{
51    CMPXCHG_LOOP(
52        new.count++;
53    ,
54        return;
55    );
56
57    spin_lock(&lockref->lock);
58    lockref->count++;
59    spin_unlock(&lockref->lock);
60}
61EXPORT_SYMBOL(lockref_get);
62
63/**
64 * lockref_get_not_zero - Increments count unless the count is 0
65 * @lockref: pointer to lockref structure
66 * Return: 1 if count updated successfully or 0 if count was zero
67 */
68int lockref_get_not_zero(struct lockref *lockref)
69{
70    int retval;
71
72    CMPXCHG_LOOP(
73        new.count++;
74        if (!old.count)
75            return 0;
76    ,
77        return 1;
78    );
79
80    spin_lock(&lockref->lock);
81    retval = 0;
82    if (lockref->count) {
83        lockref->count++;
84        retval = 1;
85    }
86    spin_unlock(&lockref->lock);
87    return retval;
88}
89EXPORT_SYMBOL(lockref_get_not_zero);
90
91/**
92 * lockref_get_or_lock - Increments count unless the count is 0
93 * @lockref: pointer to lockref structure
94 * Return: 1 if count updated successfully or 0 if count was zero
95 * and we got the lock instead.
96 */
97int lockref_get_or_lock(struct lockref *lockref)
98{
99    CMPXCHG_LOOP(
100        new.count++;
101        if (!old.count)
102            break;
103    ,
104        return 1;
105    );
106
107    spin_lock(&lockref->lock);
108    if (!lockref->count)
109        return 0;
110    lockref->count++;
111    spin_unlock(&lockref->lock);
112    return 1;
113}
114EXPORT_SYMBOL(lockref_get_or_lock);
115
116/**
117 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
118 * @lockref: pointer to lockref structure
119 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
120 */
121int lockref_put_or_lock(struct lockref *lockref)
122{
123    CMPXCHG_LOOP(
124        new.count--;
125        if (old.count <= 1)
126            break;
127    ,
128        return 1;
129    );
130
131    spin_lock(&lockref->lock);
132    if (lockref->count <= 1)
133        return 0;
134    lockref->count--;
135    spin_unlock(&lockref->lock);
136    return 1;
137}
138EXPORT_SYMBOL(lockref_put_or_lock);
139
140/**
141 * lockref_mark_dead - mark lockref dead
142 * @lockref: pointer to lockref structure
143 */
144void lockref_mark_dead(struct lockref *lockref)
145{
146    assert_spin_locked(&lockref->lock);
147    lockref->count = -128;
148}
149EXPORT_SYMBOL(lockref_mark_dead);
150
151/**
152 * lockref_get_not_dead - Increments count unless the ref is dead
153 * @lockref: pointer to lockref structure
154 * Return: 1 if count updated successfully or 0 if lockref was dead
155 */
156int lockref_get_not_dead(struct lockref *lockref)
157{
158    int retval;
159
160    CMPXCHG_LOOP(
161        new.count++;
162        if ((int)old.count < 0)
163            return 0;
164    ,
165        return 1;
166    );
167
168    spin_lock(&lockref->lock);
169    retval = 0;
170    if ((int) lockref->count >= 0) {
171        lockref->count++;
172        retval = 1;
173    }
174    spin_unlock(&lockref->lock);
175    return retval;
176}
177EXPORT_SYMBOL(lockref_get_not_dead);
178

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