1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/export.h>
3 #include <linux/lockref.h>
4
5 #if USE_CMPXCHG_LOCKREF
6
7 /*
8 * Note that the "cmpxchg()" reloads the "old" value for the
9 * failure case.
10 */
11 #define CMPXCHG_LOOP(CODE, SUCCESS) do { \
12 int retry = 100; \
13 struct lockref old; \
14 BUILD_BUG_ON(sizeof(old) != 8); \
15 old.lock_count = READ_ONCE(lockref->lock_count); \
16 while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
17 struct lockref new = old; \
18 CODE \
19 if (likely(try_cmpxchg64_relaxed(&lockref->lock_count, \
20 &old.lock_count, \
21 new.lock_count))) { \
22 SUCCESS; \
23 } \
24 if (!--retry) \
25 break; \
26 } \
27 } while (0)
28
29 #else
30
31 #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
32
33 #endif
34
35 /**
36 * lockref_get - Increments reference count unconditionally
37 * @lockref: pointer to lockref structure
38 *
39 * This operation is only valid if you already hold a reference
40 * to the object, so you know the count cannot be zero.
41 */
42 void lockref_get(struct lockref *lockref)
43 {
44 CMPXCHG_LOOP(
45 new.count++;
46 ,
47 return;
48 );
49
50 spin_lock(&lockref->lock);
51 lockref->count++;
52 spin_unlock(&lockref->lock);
53 }
54 EXPORT_SYMBOL(lockref_get);
55
56 /**
57 * lockref_get_not_zero - Increments count unless the count is 0 or dead
58 * @lockref: pointer to lockref structure
59 * Return: 1 if count updated successfully or 0 if count was zero
60 */
61 int lockref_get_not_zero(struct lockref *lockref)
62 {
63 int retval;
64
65 CMPXCHG_LOOP(
66 new.count++;
67 if (old.count <= 0)
68 return 0;
69 ,
70 return 1;
71 );
72
73 spin_lock(&lockref->lock);
74 retval = 0;
75 if (lockref->count > 0) {
76 lockref->count++;
77 retval = 1;
78 }
79 spin_unlock(&lockref->lock);
80 return retval;
81 }
82 EXPORT_SYMBOL(lockref_get_not_zero);
83
84 /**
85 * lockref_put_not_zero - Decrements count unless count <= 1 before decrement
86 * @lockref: pointer to lockref structure
87 * Return: 1 if count updated successfully or 0 if count would become zero
88 */
89 int lockref_put_not_zero(struct lockref *lockref)
90 {
91 int retval;
92
93 CMPXCHG_LOOP(
94 new.count--;
95 if (old.count <= 1)
96 return 0;
97 ,
98 return 1;
99 );
100
101 spin_lock(&lockref->lock);
102 retval = 0;
103 if (lockref->count > 1) {
104 lockref->count--;
105 retval = 1;
106 }
107 spin_unlock(&lockref->lock);
108 return retval;
109 }
110 EXPORT_SYMBOL(lockref_put_not_zero);
111
112 /**
113 * lockref_put_return - Decrement reference count if possible
114 * @lockref: pointer to lockref structure
115 *
116 * Decrement the reference count and return the new value.
117 * If the lockref was dead or locked, return an error.
118 */
119 int lockref_put_return(struct lockref *lockref)
120 {
121 CMPXCHG_LOOP(
122 new.count--;
123 if (old.count <= 0)
124 return -1;
125 ,
126 return new.count;
127 );
128 return -1;
129 }
130 EXPORT_SYMBOL(lockref_put_return);
131
132 /**
133 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
134 * @lockref: pointer to lockref structure
135 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
136 */
137 int lockref_put_or_lock(struct lockref *lockref)
138 {
139 CMPXCHG_LOOP(
140 new.count--;
141 if (old.count <= 1)
142 break;
143 ,
144 return 1;
145 );
146
147 spin_lock(&lockref->lock);
148 if (lockref->count <= 1)
149 return 0;
150 lockref->count--;
151 spin_unlock(&lockref->lock);
152 return 1;
153 }
154 EXPORT_SYMBOL(lockref_put_or_lock);
155
156 /**
157 * lockref_mark_dead - mark lockref dead
158 * @lockref: pointer to lockref structure
159 */
160 void lockref_mark_dead(struct lockref *lockref)
161 {
162 assert_spin_locked(&lockref->lock);
163 lockref->count = -128;
164 }
165 EXPORT_SYMBOL(lockref_mark_dead);
166
167 /**
168 * lockref_get_not_dead - Increments count unless the ref is dead
169 * @lockref: pointer to lockref structure
170 * Return: 1 if count updated successfully or 0 if lockref was dead
171 */
172 int lockref_get_not_dead(struct lockref *lockref)
173 {
174 int retval;
175
176 CMPXCHG_LOOP(
177 new.count++;
178 if (old.count < 0)
179 return 0;
180 ,
181 return 1;
182 );
183
184 spin_lock(&lockref->lock);
185 retval = 0;
186 if (lockref->count >= 0) {
187 lockref->count++;
188 retval = 1;
189 }
190 spin_unlock(&lockref->lock);
191 return retval;
192 }
193 EXPORT_SYMBOL(lockref_get_not_dead);
194
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