summaryrefslogtreecommitdiffstats
path: root/include/linux/rcuref.h
blob: e1adbba14b67283fc534e8431b97ad7b694d4adb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
/*
 * rcuref.h
 *
 * Reference counting for elements of lists/arrays protected by
 * RCU.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2005
 *
 * Author: Dipankar Sarma <dipankar@in.ibm.com>
 *	   Ravikiran Thirumalai <kiran_th@gmail.com>
 *
 * See Documentation/RCU/rcuref.txt for detailed user guide.
 *
 */

#ifndef _RCUREF_H_
#define _RCUREF_H_

#ifdef __KERNEL__

#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>

/*
 * These APIs work on traditional atomic_t counters used in the
 * kernel for reference counting. Under special circumstances
 * where a lock-free get() operation races with a put() operation
 * these APIs can be used. See Documentation/RCU/rcuref.txt.
 */

#ifdef __HAVE_ARCH_CMPXCHG

/**
 * rcuref_inc - increment refcount for object.
 * @rcuref: reference counter in the object in question.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference
 * in a lock-free reader-side critical section.
 */
static inline void rcuref_inc(atomic_t *rcuref)
{
	atomic_inc(rcuref);
}

/**
 * rcuref_dec - decrement refcount for object.
 * @rcuref: reference counter in the object in question.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference
 * in a lock-free reader-side critical section.
 */
static inline void rcuref_dec(atomic_t *rcuref)
{
	atomic_dec(rcuref);
}

/**
 * rcuref_dec_and_test - decrement refcount for object and test
 * @rcuref: reference counter in the object.
 * @release: pointer to the function that will clean up the object
 *	     when the last reference to the object is released.
 *	     This pointer is required.
 *
 * Decrement the refcount, and if 0, return 1. Else return 0.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference
 * in a lock-free reader-side critical section.
 */
static inline int rcuref_dec_and_test(atomic_t *rcuref)
{
	return atomic_dec_and_test(rcuref);
}

/*
 * cmpxchg is needed on UP too, if deletions to the list/array can happen
 * in interrupt context.
 */

/**
 * rcuref_inc_lf - Take reference to an object in a read-side
 * critical section protected by RCU.
 * @rcuref: reference counter in the object in question.
 *
 * Try and increment the refcount by 1.  The increment might fail if
 * the reference counter has been through a 1 to 0 transition and
 * is no longer part of the lock-free list.
 * Returns non-zero on successful increment and zero otherwise.
 */
static inline int rcuref_inc_lf(atomic_t *rcuref)
{
	int c, old;
	c = atomic_read(rcuref);
	while (c && (old = cmpxchg(&rcuref->counter, c, c + 1)) != c)
		c = old;
	return c;
}

#else				/* !__HAVE_ARCH_CMPXCHG */

extern spinlock_t __rcuref_hash[];

/*
 * Use a hash table of locks to protect the reference count
 * since cmpxchg is not available in this arch.
 */
#ifdef	CONFIG_SMP
#define RCUREF_HASH_SIZE	4
#define RCUREF_HASH(k) \
	(&__rcuref_hash[(((unsigned long)k)>>8) & (RCUREF_HASH_SIZE-1)])
#else
#define	RCUREF_HASH_SIZE	1
#define RCUREF_HASH(k) 	&__rcuref_hash[0]
#endif				/* CONFIG_SMP */

/**
 * rcuref_inc - increment refcount for object.
 * @rcuref: reference counter in the object in question.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference in a lock-free
 * reader-side critical section.
 */
static inline void rcuref_inc(atomic_t *rcuref)
{
	unsigned long flags;
	spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
	rcuref->counter += 1;
	spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
}

/**
 * rcuref_dec - decrement refcount for object.
 * @rcuref: reference counter in the object in question.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference in a lock-free
 * reader-side critical section.
 */
static inline void rcuref_dec(atomic_t *rcuref)
{
	unsigned long flags;
	spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
	rcuref->counter -= 1;
	spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
}

/**
 * rcuref_dec_and_test - decrement refcount for object and test
 * @rcuref: reference counter in the object.
 * @release: pointer to the function that will clean up the object
 *	     when the last reference to the object is released.
 *	     This pointer is required.
 *
 * Decrement the refcount, and if 0, return 1. Else return 0.
 *
 * This should be used only for objects where we use RCU and
 * use the rcuref_inc_lf() api to acquire a reference in a lock-free
 * reader-side critical section.
 */
static inline int rcuref_dec_and_test(atomic_t *rcuref)
{
	unsigned long flags;
	spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
	rcuref->counter--;
	if (!rcuref->counter) {
		spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
		return 1;
	} else {
		spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
		return 0;
	}
}

/**
 * rcuref_inc_lf - Take reference to an object of a lock-free collection
 * by traversing a lock-free list/array.
 * @rcuref: reference counter in the object in question.
 *
 * Try and increment the refcount by 1.  The increment might fail if
 * the reference counter has been through a 1 to 0 transition and
 * object is no longer part of the lock-free list.
 * Returns non-zero on successful increment and zero otherwise.
 */
static inline int rcuref_inc_lf(atomic_t *rcuref)
{
	int ret;
	unsigned long flags;
	spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
	if (rcuref->counter)
		ret = rcuref->counter++;
	else
		ret = 0;
	spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
	return ret;
}


#endif /* !__HAVE_ARCH_CMPXCHG */

#endif /* __KERNEL__ */
#endif /* _RCUREF_H_ */