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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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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 | */ | |
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); |