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1 | #include <linux/export.h> | |
2 | #include <linux/lockref.h> | |
3 | ||
4 | #if USE_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 = READ_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 = cmpxchg64_relaxed(&lockref->lock_count, \ | |
18 | old.lock_count, \ | |
19 | new.lock_count); \ | |
20 | if (likely(old.lock_count == prev.lock_count)) { \ | |
21 | SUCCESS; \ | |
22 | } \ | |
23 | cpu_relax(); \ | |
24 | } \ | |
25 | } while (0) | |
26 | ||
27 | #else | |
28 | ||
29 | #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0) | |
30 | ||
31 | #endif | |
32 | ||
33 | /** | |
34 | * lockref_get - Increments reference count unconditionally | |
35 | * @lockref: pointer to lockref structure | |
36 | * | |
37 | * This operation is only valid if you already hold a reference | |
38 | * to the object, so you know the count cannot be zero. | |
39 | */ | |
40 | void lockref_get(struct lockref *lockref) | |
41 | { | |
42 | CMPXCHG_LOOP( | |
43 | new.count++; | |
44 | , | |
45 | return; | |
46 | ); | |
47 | ||
48 | spin_lock(&lockref->lock); | |
49 | lockref->count++; | |
50 | spin_unlock(&lockref->lock); | |
51 | } | |
52 | EXPORT_SYMBOL(lockref_get); | |
53 | ||
54 | /** | |
55 | * lockref_get_not_zero - Increments count unless the count is 0 or dead | |
56 | * @lockref: pointer to lockref structure | |
57 | * Return: 1 if count updated successfully or 0 if count was zero | |
58 | */ | |
59 | int lockref_get_not_zero(struct lockref *lockref) | |
60 | { | |
61 | int retval; | |
62 | ||
63 | CMPXCHG_LOOP( | |
64 | new.count++; | |
65 | if (old.count <= 0) | |
66 | return 0; | |
67 | , | |
68 | return 1; | |
69 | ); | |
70 | ||
71 | spin_lock(&lockref->lock); | |
72 | retval = 0; | |
73 | if (lockref->count > 0) { | |
74 | lockref->count++; | |
75 | retval = 1; | |
76 | } | |
77 | spin_unlock(&lockref->lock); | |
78 | return retval; | |
79 | } | |
80 | EXPORT_SYMBOL(lockref_get_not_zero); | |
81 | ||
82 | /** | |
83 | * lockref_get_or_lock - Increments count unless the count is 0 or dead | |
84 | * @lockref: pointer to lockref structure | |
85 | * Return: 1 if count updated successfully or 0 if count was zero | |
86 | * and we got the lock instead. | |
87 | */ | |
88 | int lockref_get_or_lock(struct lockref *lockref) | |
89 | { | |
90 | CMPXCHG_LOOP( | |
91 | new.count++; | |
92 | if (old.count <= 0) | |
93 | break; | |
94 | , | |
95 | return 1; | |
96 | ); | |
97 | ||
98 | spin_lock(&lockref->lock); | |
99 | if (lockref->count <= 0) | |
100 | return 0; | |
101 | lockref->count++; | |
102 | spin_unlock(&lockref->lock); | |
103 | return 1; | |
104 | } | |
105 | EXPORT_SYMBOL(lockref_get_or_lock); | |
106 | ||
107 | /** | |
108 | * lockref_put_return - Decrement reference count if possible | |
109 | * @lockref: pointer to lockref structure | |
110 | * | |
111 | * Decrement the reference count and return the new value. | |
112 | * If the lockref was dead or locked, return an error. | |
113 | */ | |
114 | int lockref_put_return(struct lockref *lockref) | |
115 | { | |
116 | CMPXCHG_LOOP( | |
117 | new.count--; | |
118 | if (old.count <= 0) | |
119 | return -1; | |
120 | , | |
121 | return new.count; | |
122 | ); | |
123 | return -1; | |
124 | } | |
125 | EXPORT_SYMBOL(lockref_put_return); | |
126 | ||
127 | /** | |
128 | * lockref_put_or_lock - decrements count unless count <= 1 before decrement | |
129 | * @lockref: pointer to lockref structure | |
130 | * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken | |
131 | */ | |
132 | int lockref_put_or_lock(struct lockref *lockref) | |
133 | { | |
134 | CMPXCHG_LOOP( | |
135 | new.count--; | |
136 | if (old.count <= 1) | |
137 | break; | |
138 | , | |
139 | return 1; | |
140 | ); | |
141 | ||
142 | spin_lock(&lockref->lock); | |
143 | if (lockref->count <= 1) | |
144 | return 0; | |
145 | lockref->count--; | |
146 | spin_unlock(&lockref->lock); | |
147 | return 1; | |
148 | } | |
149 | EXPORT_SYMBOL(lockref_put_or_lock); | |
150 | ||
151 | /** | |
152 | * lockref_mark_dead - mark lockref dead | |
153 | * @lockref: pointer to lockref structure | |
154 | */ | |
155 | void lockref_mark_dead(struct lockref *lockref) | |
156 | { | |
157 | assert_spin_locked(&lockref->lock); | |
158 | lockref->count = -128; | |
159 | } | |
160 | EXPORT_SYMBOL(lockref_mark_dead); | |
161 | ||
162 | /** | |
163 | * lockref_get_not_dead - Increments count unless the ref is dead | |
164 | * @lockref: pointer to lockref structure | |
165 | * Return: 1 if count updated successfully or 0 if lockref was dead | |
166 | */ | |
167 | int lockref_get_not_dead(struct lockref *lockref) | |
168 | { | |
169 | int retval; | |
170 | ||
171 | CMPXCHG_LOOP( | |
172 | new.count++; | |
173 | if (old.count < 0) | |
174 | return 0; | |
175 | , | |
176 | return 1; | |
177 | ); | |
178 | ||
179 | spin_lock(&lockref->lock); | |
180 | retval = 0; | |
181 | if (lockref->count >= 0) { | |
182 | lockref->count++; | |
183 | retval = 1; | |
184 | } | |
185 | spin_unlock(&lockref->lock); | |
186 | return retval; | |
187 | } | |
188 | EXPORT_SYMBOL(lockref_get_not_dead); |