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1#include <linux/export.h>
2#include <linux/lockref.h>
3#include <linux/mutex.h>
4
5#if USE_CMPXCHG_LOCKREF
6
7/*
8 * Allow weakly-ordered memory architectures to provide barrier-less
9 * cmpxchg semantics for lockref updates.
10 */
11#ifndef cmpxchg64_relaxed
12# define cmpxchg64_relaxed cmpxchg64
13#endif
14
15/*
16 * Note that the "cmpxchg()" reloads the "old" value for the
17 * failure case.
18 */
19#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
20 struct lockref old; \
21 BUILD_BUG_ON(sizeof(old) != 8); \
22 old.lock_count = ACCESS_ONCE(lockref->lock_count); \
23 while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
24 struct lockref new = old, prev = old; \
25 CODE \
26 old.lock_count = cmpxchg64_relaxed(&lockref->lock_count, \
27 old.lock_count, \
28 new.lock_count); \
29 if (likely(old.lock_count == prev.lock_count)) { \
30 SUCCESS; \
31 } \
32 arch_mutex_cpu_relax(); \
33 } \
34} while (0)
35
36#else
37
38#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
39
40#endif
41
42/**
43 * lockref_get - Increments reference count unconditionally
44 * @lockref: pointer to lockref structure
45 *
46 * This operation is only valid if you already hold a reference
47 * to the object, so you know the count cannot be zero.
48 */
49void lockref_get(struct lockref *lockref)
50{
51 CMPXCHG_LOOP(
52 new.count++;
53 ,
54 return;
55 );
56
57 spin_lock(&lockref->lock);
58 lockref->count++;
59 spin_unlock(&lockref->lock);
60}
61EXPORT_SYMBOL(lockref_get);
62
63/**
64 * lockref_get_not_zero - Increments count unless the count is 0
65 * @lockref: pointer to lockref structure
66 * Return: 1 if count updated successfully or 0 if count was zero
67 */
68int lockref_get_not_zero(struct lockref *lockref)
69{
70 int retval;
71
72 CMPXCHG_LOOP(
73 new.count++;
74 if (!old.count)
75 return 0;
76 ,
77 return 1;
78 );
79
80 spin_lock(&lockref->lock);
81 retval = 0;
82 if (lockref->count) {
83 lockref->count++;
84 retval = 1;
85 }
86 spin_unlock(&lockref->lock);
87 return retval;
88}
89EXPORT_SYMBOL(lockref_get_not_zero);
90
91/**
92 * lockref_get_or_lock - Increments count unless the count is 0
93 * @lockref: pointer to lockref structure
94 * Return: 1 if count updated successfully or 0 if count was zero
95 * and we got the lock instead.
96 */
97int lockref_get_or_lock(struct lockref *lockref)
98{
99 CMPXCHG_LOOP(
100 new.count++;
101 if (!old.count)
102 break;
103 ,
104 return 1;
105 );
106
107 spin_lock(&lockref->lock);
108 if (!lockref->count)
109 return 0;
110 lockref->count++;
111 spin_unlock(&lockref->lock);
112 return 1;
113}
114EXPORT_SYMBOL(lockref_get_or_lock);
115
116/**
117 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
118 * @lockref: pointer to lockref structure
119 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
120 */
121int lockref_put_or_lock(struct lockref *lockref)
122{
123 CMPXCHG_LOOP(
124 new.count--;
125 if (old.count <= 1)
126 break;
127 ,
128 return 1;
129 );
130
131 spin_lock(&lockref->lock);
132 if (lockref->count <= 1)
133 return 0;
134 lockref->count--;
135 spin_unlock(&lockref->lock);
136 return 1;
137}
138EXPORT_SYMBOL(lockref_put_or_lock);
139
140/**
141 * lockref_mark_dead - mark lockref dead
142 * @lockref: pointer to lockref structure
143 */
144void lockref_mark_dead(struct lockref *lockref)
145{
146 assert_spin_locked(&lockref->lock);
147 lockref->count = -128;
148}
149EXPORT_SYMBOL(lockref_mark_dead);
150
151/**
152 * lockref_get_not_dead - Increments count unless the ref is dead
153 * @lockref: pointer to lockref structure
154 * Return: 1 if count updated successfully or 0 if lockref was dead
155 */
156int lockref_get_not_dead(struct lockref *lockref)
157{
158 int retval;
159
160 CMPXCHG_LOOP(
161 new.count++;
162 if ((int)old.count < 0)
163 return 0;
164 ,
165 return 1;
166 );
167
168 spin_lock(&lockref->lock);
169 retval = 0;
170 if ((int) lockref->count >= 0) {
171 lockref->count++;
172 retval = 1;
173 }
174 spin_unlock(&lockref->lock);
175 return retval;
176}
177EXPORT_SYMBOL(lockref_get_not_dead);
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 */
44void 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}
56EXPORT_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 */
63int 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}
84EXPORT_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 */
91int 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}
112EXPORT_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 */
120int 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}
137EXPORT_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 */
146int 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}
157EXPORT_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 */
164int 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}
181EXPORT_SYMBOL(lockref_put_or_lock);
182
183/**
184 * lockref_mark_dead - mark lockref dead
185 * @lockref: pointer to lockref structure
186 */
187void lockref_mark_dead(struct lockref *lockref)
188{
189 assert_spin_locked(&lockref->lock);
190 lockref->count = -128;
191}
192EXPORT_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 */
199int 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}
220EXPORT_SYMBOL(lockref_get_not_dead);