blob: 5a92189ad711af195f501fce9a3c5e2844ed11a1
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_lowlatency(); \ |
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); |
189 |