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1 | /* |
2 | * rcuref.h | |
3 | * | |
4 | * Reference counting for elements of lists/arrays protected by | |
5 | * RCU. | |
6 | * | |
7 | * This program is free software; you can redistribute it and/or modify | |
8 | * it under the terms of the GNU General Public License as published by | |
9 | * the Free Software Foundation; either version 2 of the License, or | |
10 | * (at your option) any later version. | |
11 | * | |
12 | * This program is distributed in the hope that it will be useful, | |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | * GNU General Public License for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU General Public License | |
18 | * along with this program; if not, write to the Free Software | |
19 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
20 | * | |
21 | * Copyright (C) IBM Corporation, 2005 | |
22 | * | |
23 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
24 | * Ravikiran Thirumalai <kiran_th@gmail.com> | |
25 | * | |
26 | * See Documentation/RCU/rcuref.txt for detailed user guide. | |
27 | * | |
28 | */ | |
29 | ||
30 | #ifndef _RCUREF_H_ | |
31 | #define _RCUREF_H_ | |
32 | ||
33 | #ifdef __KERNEL__ | |
34 | ||
35 | #include <linux/types.h> | |
36 | #include <linux/interrupt.h> | |
37 | #include <linux/spinlock.h> | |
38 | #include <asm/atomic.h> | |
39 | ||
40 | /* | |
41 | * These APIs work on traditional atomic_t counters used in the | |
42 | * kernel for reference counting. Under special circumstances | |
43 | * where a lock-free get() operation races with a put() operation | |
44 | * these APIs can be used. See Documentation/RCU/rcuref.txt. | |
45 | */ | |
46 | ||
47 | #ifdef __HAVE_ARCH_CMPXCHG | |
48 | ||
49 | /** | |
50 | * rcuref_inc - increment refcount for object. | |
51 | * @rcuref: reference counter in the object in question. | |
52 | * | |
53 | * This should be used only for objects where we use RCU and | |
54 | * use the rcuref_inc_lf() api to acquire a reference | |
55 | * in a lock-free reader-side critical section. | |
56 | */ | |
57 | static inline void rcuref_inc(atomic_t *rcuref) | |
58 | { | |
59 | atomic_inc(rcuref); | |
60 | } | |
61 | ||
62 | /** | |
63 | * rcuref_dec - decrement refcount for object. | |
64 | * @rcuref: reference counter in the object in question. | |
65 | * | |
66 | * This should be used only for objects where we use RCU and | |
67 | * use the rcuref_inc_lf() api to acquire a reference | |
68 | * in a lock-free reader-side critical section. | |
69 | */ | |
70 | static inline void rcuref_dec(atomic_t *rcuref) | |
71 | { | |
72 | atomic_dec(rcuref); | |
73 | } | |
74 | ||
75 | /** | |
76 | * rcuref_dec_and_test - decrement refcount for object and test | |
77 | * @rcuref: reference counter in the object. | |
78 | * @release: pointer to the function that will clean up the object | |
79 | * when the last reference to the object is released. | |
80 | * This pointer is required. | |
81 | * | |
82 | * Decrement the refcount, and if 0, return 1. Else return 0. | |
83 | * | |
84 | * This should be used only for objects where we use RCU and | |
85 | * use the rcuref_inc_lf() api to acquire a reference | |
86 | * in a lock-free reader-side critical section. | |
87 | */ | |
88 | static inline int rcuref_dec_and_test(atomic_t *rcuref) | |
89 | { | |
90 | return atomic_dec_and_test(rcuref); | |
91 | } | |
92 | ||
93 | /* | |
94 | * cmpxchg is needed on UP too, if deletions to the list/array can happen | |
95 | * in interrupt context. | |
96 | */ | |
97 | ||
98 | /** | |
99 | * rcuref_inc_lf - Take reference to an object in a read-side | |
100 | * critical section protected by RCU. | |
101 | * @rcuref: reference counter in the object in question. | |
102 | * | |
103 | * Try and increment the refcount by 1. The increment might fail if | |
104 | * the reference counter has been through a 1 to 0 transition and | |
105 | * is no longer part of the lock-free list. | |
106 | * Returns non-zero on successful increment and zero otherwise. | |
107 | */ | |
108 | static inline int rcuref_inc_lf(atomic_t *rcuref) | |
109 | { | |
110 | int c, old; | |
111 | c = atomic_read(rcuref); | |
112 | while (c && (old = cmpxchg(&rcuref->counter, c, c + 1)) != c) | |
113 | c = old; | |
114 | return c; | |
115 | } | |
116 | ||
117 | #else /* !__HAVE_ARCH_CMPXCHG */ | |
118 | ||
119 | extern spinlock_t __rcuref_hash[]; | |
120 | ||
121 | /* | |
122 | * Use a hash table of locks to protect the reference count | |
123 | * since cmpxchg is not available in this arch. | |
124 | */ | |
125 | #ifdef CONFIG_SMP | |
126 | #define RCUREF_HASH_SIZE 4 | |
127 | #define RCUREF_HASH(k) \ | |
128 | (&__rcuref_hash[(((unsigned long)k)>>8) & (RCUREF_HASH_SIZE-1)]) | |
129 | #else | |
130 | #define RCUREF_HASH_SIZE 1 | |
131 | #define RCUREF_HASH(k) &__rcuref_hash[0] | |
132 | #endif /* CONFIG_SMP */ | |
133 | ||
134 | /** | |
135 | * rcuref_inc - increment refcount for object. | |
136 | * @rcuref: reference counter in the object in question. | |
137 | * | |
138 | * This should be used only for objects where we use RCU and | |
139 | * use the rcuref_inc_lf() api to acquire a reference in a lock-free | |
140 | * reader-side critical section. | |
141 | */ | |
142 | static inline void rcuref_inc(atomic_t *rcuref) | |
143 | { | |
144 | unsigned long flags; | |
145 | spin_lock_irqsave(RCUREF_HASH(rcuref), flags); | |
146 | rcuref->counter += 1; | |
147 | spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags); | |
148 | } | |
149 | ||
150 | /** | |
151 | * rcuref_dec - decrement refcount for object. | |
152 | * @rcuref: reference counter in the object in question. | |
153 | * | |
154 | * This should be used only for objects where we use RCU and | |
155 | * use the rcuref_inc_lf() api to acquire a reference in a lock-free | |
156 | * reader-side critical section. | |
157 | */ | |
158 | static inline void rcuref_dec(atomic_t *rcuref) | |
159 | { | |
160 | unsigned long flags; | |
161 | spin_lock_irqsave(RCUREF_HASH(rcuref), flags); | |
162 | rcuref->counter -= 1; | |
163 | spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags); | |
164 | } | |
165 | ||
166 | /** | |
167 | * rcuref_dec_and_test - decrement refcount for object and test | |
168 | * @rcuref: reference counter in the object. | |
169 | * @release: pointer to the function that will clean up the object | |
170 | * when the last reference to the object is released. | |
171 | * This pointer is required. | |
172 | * | |
173 | * Decrement the refcount, and if 0, return 1. Else return 0. | |
174 | * | |
175 | * This should be used only for objects where we use RCU and | |
176 | * use the rcuref_inc_lf() api to acquire a reference in a lock-free | |
177 | * reader-side critical section. | |
178 | */ | |
179 | static inline int rcuref_dec_and_test(atomic_t *rcuref) | |
180 | { | |
181 | unsigned long flags; | |
182 | spin_lock_irqsave(RCUREF_HASH(rcuref), flags); | |
183 | rcuref->counter--; | |
184 | if (!rcuref->counter) { | |
185 | spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags); | |
186 | return 1; | |
187 | } else { | |
188 | spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags); | |
189 | return 0; | |
190 | } | |
191 | } | |
192 | ||
193 | /** | |
194 | * rcuref_inc_lf - Take reference to an object of a lock-free collection | |
195 | * by traversing a lock-free list/array. | |
196 | * @rcuref: reference counter in the object in question. | |
197 | * | |
198 | * Try and increment the refcount by 1. The increment might fail if | |
199 | * the reference counter has been through a 1 to 0 transition and | |
200 | * object is no longer part of the lock-free list. | |
201 | * Returns non-zero on successful increment and zero otherwise. | |
202 | */ | |
203 | static inline int rcuref_inc_lf(atomic_t *rcuref) | |
204 | { | |
205 | int ret; | |
206 | unsigned long flags; | |
207 | spin_lock_irqsave(RCUREF_HASH(rcuref), flags); | |
208 | if (rcuref->counter) | |
209 | ret = rcuref->counter++; | |
210 | else | |
211 | ret = 0; | |
212 | spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags); | |
213 | return ret; | |
214 | } | |
215 | ||
216 | ||
217 | #endif /* !__HAVE_ARCH_CMPXCHG */ | |
218 | ||
219 | #endif /* __KERNEL__ */ | |
220 | #endif /* _RCUREF_H_ */ |