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, prev = old; \
18 CODE \
19 old.lock_count = cmpxchg64_relaxed(&lockref->lock_count, \
20 old.lock_count, \
21 new.lock_count); \
22 if (likely(old.lock_count == prev.lock_count)) { \
23 SUCCESS; \
24 } \
25 if (!--retry) \
26 break; \
27 cpu_relax(); \
28 } \
29 } while (0)
30
31 #else
32
33 #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
34
35 #endif
36
37 /**
38 * lockref_get - Increments reference count unconditionally
39 * @lockref: pointer to lockref structure
40 *
41 * This operation is only valid if you already hold a reference
42 * to the object, so you know the count cannot be zero.
43 */
lockref_get(struct lockref * lockref)44 void lockref_get(struct lockref *lockref)
45 {
46 CMPXCHG_LOOP(
47 new.count++;
48 ,
49 return;
50 );
51
52 spin_lock(&lockref->lock);
53 lockref->count++;
54 spin_unlock(&lockref->lock);
55 }
56 EXPORT_SYMBOL(lockref_get);
57
58 /**
59 * lockref_get_not_zero - Increments count unless the count is 0 or dead
60 * @lockref: pointer to lockref structure
61 * Return: 1 if count updated successfully or 0 if count was zero
62 */
lockref_get_not_zero(struct lockref * lockref)63 int lockref_get_not_zero(struct lockref *lockref)
64 {
65 int retval;
66
67 CMPXCHG_LOOP(
68 new.count++;
69 if (old.count <= 0)
70 return 0;
71 ,
72 return 1;
73 );
74
75 spin_lock(&lockref->lock);
76 retval = 0;
77 if (lockref->count > 0) {
78 lockref->count++;
79 retval = 1;
80 }
81 spin_unlock(&lockref->lock);
82 return retval;
83 }
84 EXPORT_SYMBOL(lockref_get_not_zero);
85
86 /**
87 * lockref_put_not_zero - Decrements count unless count <= 1 before decrement
88 * @lockref: pointer to lockref structure
89 * Return: 1 if count updated successfully or 0 if count would become zero
90 */
lockref_put_not_zero(struct lockref * lockref)91 int lockref_put_not_zero(struct lockref *lockref)
92 {
93 int retval;
94
95 CMPXCHG_LOOP(
96 new.count--;
97 if (old.count <= 1)
98 return 0;
99 ,
100 return 1;
101 );
102
103 spin_lock(&lockref->lock);
104 retval = 0;
105 if (lockref->count > 1) {
106 lockref->count--;
107 retval = 1;
108 }
109 spin_unlock(&lockref->lock);
110 return retval;
111 }
112 EXPORT_SYMBOL(lockref_put_not_zero);
113
114 /**
115 * lockref_get_or_lock - Increments count unless the count is 0 or dead
116 * @lockref: pointer to lockref structure
117 * Return: 1 if count updated successfully or 0 if count was zero
118 * and we got the lock instead.
119 */
lockref_get_or_lock(struct lockref * lockref)120 int lockref_get_or_lock(struct lockref *lockref)
121 {
122 CMPXCHG_LOOP(
123 new.count++;
124 if (old.count <= 0)
125 break;
126 ,
127 return 1;
128 );
129
130 spin_lock(&lockref->lock);
131 if (lockref->count <= 0)
132 return 0;
133 lockref->count++;
134 spin_unlock(&lockref->lock);
135 return 1;
136 }
137 EXPORT_SYMBOL(lockref_get_or_lock);
138
139 /**
140 * lockref_put_return - Decrement reference count if possible
141 * @lockref: pointer to lockref structure
142 *
143 * Decrement the reference count and return the new value.
144 * If the lockref was dead or locked, return an error.
145 */
lockref_put_return(struct lockref * lockref)146 int lockref_put_return(struct lockref *lockref)
147 {
148 CMPXCHG_LOOP(
149 new.count--;
150 if (old.count <= 0)
151 return -1;
152 ,
153 return new.count;
154 );
155 return -1;
156 }
157 EXPORT_SYMBOL(lockref_put_return);
158
159 /**
160 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
161 * @lockref: pointer to lockref structure
162 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
163 */
lockref_put_or_lock(struct lockref * lockref)164 int lockref_put_or_lock(struct lockref *lockref)
165 {
166 CMPXCHG_LOOP(
167 new.count--;
168 if (old.count <= 1)
169 break;
170 ,
171 return 1;
172 );
173
174 spin_lock(&lockref->lock);
175 if (lockref->count <= 1)
176 return 0;
177 lockref->count--;
178 spin_unlock(&lockref->lock);
179 return 1;
180 }
181 EXPORT_SYMBOL(lockref_put_or_lock);
182
183 /**
184 * lockref_mark_dead - mark lockref dead
185 * @lockref: pointer to lockref structure
186 */
lockref_mark_dead(struct lockref * lockref)187 void lockref_mark_dead(struct lockref *lockref)
188 {
189 assert_spin_locked(&lockref->lock);
190 lockref->count = -128;
191 }
192 EXPORT_SYMBOL(lockref_mark_dead);
193
194 /**
195 * lockref_get_not_dead - Increments count unless the ref is dead
196 * @lockref: pointer to lockref structure
197 * Return: 1 if count updated successfully or 0 if lockref was dead
198 */
lockref_get_not_dead(struct lockref * lockref)199 int lockref_get_not_dead(struct lockref *lockref)
200 {
201 int retval;
202
203 CMPXCHG_LOOP(
204 new.count++;
205 if (old.count < 0)
206 return 0;
207 ,
208 return 1;
209 );
210
211 spin_lock(&lockref->lock);
212 retval = 0;
213 if (lockref->count >= 0) {
214 lockref->count++;
215 retval = 1;
216 }
217 spin_unlock(&lockref->lock);
218 return retval;
219 }
220 EXPORT_SYMBOL(lockref_get_not_dead);
221