1 /*
2 * Sleepable Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright (C) IBM Corporation, 2006
19 *
20 * Author: Paul McKenney <paulmck@us.ibm.com>
21 *
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU/ *.txt
24 *
25 */
26
27 #ifndef _LINUX_SRCU_H
28 #define _LINUX_SRCU_H
29
30 #include <linux/mutex.h>
31
32 struct srcu_struct_array {
33 int c[2];
34 };
35
36 struct srcu_struct {
37 int completed;
38 struct srcu_struct_array __percpu *per_cpu_ref;
39 struct mutex mutex;
40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
41 struct lockdep_map dep_map;
42 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
43 };
44
45 #ifndef CONFIG_PREEMPT
46 #define srcu_barrier() barrier()
47 #else /* #ifndef CONFIG_PREEMPT */
48 #define srcu_barrier()
49 #endif /* #else #ifndef CONFIG_PREEMPT */
50
51 #ifdef CONFIG_DEBUG_LOCK_ALLOC
52
53 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
54 struct lock_class_key *key);
55
56 #define init_srcu_struct(sp) \
57 ({ \
58 static struct lock_class_key __srcu_key; \
59 \
60 __init_srcu_struct((sp), #sp, &__srcu_key); \
61 })
62
63 # define srcu_read_acquire(sp) \
64 lock_acquire(&(sp)->dep_map, 0, 0, 2, 1, NULL, _THIS_IP_)
65 # define srcu_read_release(sp) \
66 lock_release(&(sp)->dep_map, 1, _THIS_IP_)
67
68 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
69
70 int init_srcu_struct(struct srcu_struct *sp);
71
72 # define srcu_read_acquire(sp) do { } while (0)
73 # define srcu_read_release(sp) do { } while (0)
74
75 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
76
77 void cleanup_srcu_struct(struct srcu_struct *sp);
78 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
79 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
80 void synchronize_srcu(struct srcu_struct *sp);
81 void synchronize_srcu_expedited(struct srcu_struct *sp);
82 long srcu_batches_completed(struct srcu_struct *sp);
83
84 #ifdef CONFIG_DEBUG_LOCK_ALLOC
85
86 /**
87 * srcu_read_lock_held - might we be in SRCU read-side critical section?
88 *
89 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
90 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
91 * this assumes we are in an SRCU read-side critical section unless it can
92 * prove otherwise.
93 */
srcu_read_lock_held(struct srcu_struct * sp)94 static inline int srcu_read_lock_held(struct srcu_struct *sp)
95 {
96 if (debug_locks)
97 return lock_is_held(&sp->dep_map);
98 return 1;
99 }
100
101 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
102
srcu_read_lock_held(struct srcu_struct * sp)103 static inline int srcu_read_lock_held(struct srcu_struct *sp)
104 {
105 return 1;
106 }
107
108 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
109
110 /**
111 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
112 * @p: the pointer to fetch and protect for later dereferencing
113 * @sp: pointer to the srcu_struct, which is used to check that we
114 * really are in an SRCU read-side critical section.
115 * @c: condition to check for update-side use
116 *
117 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
118 * critical section will result in an RCU-lockdep splat, unless @c evaluates
119 * to 1. The @c argument will normally be a logical expression containing
120 * lockdep_is_held() calls.
121 */
122 #define srcu_dereference_check(p, sp, c) \
123 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
124
125 /**
126 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
127 * @p: the pointer to fetch and protect for later dereferencing
128 * @sp: pointer to the srcu_struct, which is used to check that we
129 * really are in an SRCU read-side critical section.
130 *
131 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
132 * is enabled, invoking this outside of an RCU read-side critical
133 * section will result in an RCU-lockdep splat.
134 */
135 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
136
137 /**
138 * srcu_read_lock - register a new reader for an SRCU-protected structure.
139 * @sp: srcu_struct in which to register the new reader.
140 *
141 * Enter an SRCU read-side critical section. Note that SRCU read-side
142 * critical sections may be nested. However, it is illegal to
143 * call anything that waits on an SRCU grace period for the same
144 * srcu_struct, whether directly or indirectly. Please note that
145 * one way to indirectly wait on an SRCU grace period is to acquire
146 * a mutex that is held elsewhere while calling synchronize_srcu() or
147 * synchronize_srcu_expedited().
148 */
srcu_read_lock(struct srcu_struct * sp)149 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
150 {
151 int retval = __srcu_read_lock(sp);
152
153 srcu_read_acquire(sp);
154 return retval;
155 }
156
157 /**
158 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
159 * @sp: srcu_struct in which to unregister the old reader.
160 * @idx: return value from corresponding srcu_read_lock().
161 *
162 * Exit an SRCU read-side critical section.
163 */
srcu_read_unlock(struct srcu_struct * sp,int idx)164 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
165 __releases(sp)
166 {
167 srcu_read_release(sp);
168 __srcu_read_unlock(sp, idx);
169 }
170
171 #endif
172