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Linus Torvalds2f4f12e2013-09-02 11:58:20 -07001#include <linux/export.h>
2#include <linux/lockref.h>
3
Linus Torvaldsbc08b442013-09-02 12:12:15 -07004#ifdef CONFIG_CMPXCHG_LOCKREF
5
6/*
7 * Note that the "cmpxchg()" reloads the "old" value for the
8 * failure case.
9 */
10#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
11 struct lockref old; \
12 BUILD_BUG_ON(sizeof(old) != 8); \
13 old.lock_count = ACCESS_ONCE(lockref->lock_count); \
14 while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
15 struct lockref new = old, prev = old; \
16 CODE \
17 old.lock_count = cmpxchg(&lockref->lock_count, \
18 old.lock_count, new.lock_count); \
19 if (likely(old.lock_count == prev.lock_count)) { \
20 SUCCESS; \
21 } \
Luck, Tonyd472d9d2013-09-03 14:49:49 -070022 cpu_relax(); \
Linus Torvaldsbc08b442013-09-02 12:12:15 -070023 } \
24} while (0)
25
26#else
27
28#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
29
30#endif
31
Linus Torvalds2f4f12e2013-09-02 11:58:20 -070032/**
33 * lockref_get - Increments reference count unconditionally
34 * @lockcnt: pointer to lockref structure
35 *
36 * This operation is only valid if you already hold a reference
37 * to the object, so you know the count cannot be zero.
38 */
39void lockref_get(struct lockref *lockref)
40{
Linus Torvaldsbc08b442013-09-02 12:12:15 -070041 CMPXCHG_LOOP(
42 new.count++;
43 ,
44 return;
45 );
46
Linus Torvalds2f4f12e2013-09-02 11:58:20 -070047 spin_lock(&lockref->lock);
48 lockref->count++;
49 spin_unlock(&lockref->lock);
50}
51EXPORT_SYMBOL(lockref_get);
52
53/**
54 * lockref_get_not_zero - Increments count unless the count is 0
55 * @lockcnt: pointer to lockref structure
56 * Return: 1 if count updated successfully or 0 if count was zero
57 */
58int lockref_get_not_zero(struct lockref *lockref)
59{
Linus Torvaldsbc08b442013-09-02 12:12:15 -070060 int retval;
61
62 CMPXCHG_LOOP(
63 new.count++;
64 if (!old.count)
65 return 0;
66 ,
67 return 1;
68 );
Linus Torvalds2f4f12e2013-09-02 11:58:20 -070069
70 spin_lock(&lockref->lock);
Linus Torvaldsbc08b442013-09-02 12:12:15 -070071 retval = 0;
Linus Torvalds2f4f12e2013-09-02 11:58:20 -070072 if (lockref->count) {
73 lockref->count++;
74 retval = 1;
75 }
76 spin_unlock(&lockref->lock);
77 return retval;
78}
79EXPORT_SYMBOL(lockref_get_not_zero);
80
81/**
82 * lockref_get_or_lock - Increments count unless the count is 0
83 * @lockcnt: pointer to lockref structure
84 * Return: 1 if count updated successfully or 0 if count was zero
85 * and we got the lock instead.
86 */
87int lockref_get_or_lock(struct lockref *lockref)
88{
Linus Torvaldsbc08b442013-09-02 12:12:15 -070089 CMPXCHG_LOOP(
90 new.count++;
91 if (!old.count)
92 break;
93 ,
94 return 1;
95 );
96
Linus Torvalds2f4f12e2013-09-02 11:58:20 -070097 spin_lock(&lockref->lock);
98 if (!lockref->count)
99 return 0;
100 lockref->count++;
101 spin_unlock(&lockref->lock);
102 return 1;
103}
104EXPORT_SYMBOL(lockref_get_or_lock);
105
106/**
107 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
108 * @lockcnt: pointer to lockref structure
109 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
110 */
111int lockref_put_or_lock(struct lockref *lockref)
112{
Linus Torvaldsbc08b442013-09-02 12:12:15 -0700113 CMPXCHG_LOOP(
114 new.count--;
115 if (old.count <= 1)
116 break;
117 ,
118 return 1;
119 );
120
Linus Torvalds2f4f12e2013-09-02 11:58:20 -0700121 spin_lock(&lockref->lock);
122 if (lockref->count <= 1)
123 return 0;
124 lockref->count--;
125 spin_unlock(&lockref->lock);
126 return 1;
127}
128EXPORT_SYMBOL(lockref_put_or_lock);