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, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright (C) IBM Corporation, 2006
19 * Copyright (C) Fujitsu, 2012
20 *
21 * Author: Paul McKenney <paulmck@us.ibm.com>
22 * Lai Jiangshan <laijs@cn.fujitsu.com>
23 *
24 * For detailed explanation of Read-Copy Update mechanism see -
25 * Documentation/RCU/ *.txt
26 *
27 */
28
29 #ifndef _LINUX_SRCU_H
30 #define _LINUX_SRCU_H
31
32 #include <linux/mutex.h>
33 #include <linux/rcupdate.h>
34 #include <linux/workqueue.h>
35 #include <linux/rcu_segcblist.h>
36
37 struct srcu_struct;
38
39 #ifdef CONFIG_DEBUG_LOCK_ALLOC
40
41 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
42 struct lock_class_key *key);
43
44 #define init_srcu_struct(sp) \
45 ({ \
46 static struct lock_class_key __srcu_key; \
47 \
48 __init_srcu_struct((sp), #sp, &__srcu_key); \
49 })
50
51 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
52 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
53
54 int init_srcu_struct(struct srcu_struct *sp);
55
56 #define __SRCU_DEP_MAP_INIT(srcu_name)
57 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
58
59 #ifdef CONFIG_TINY_SRCU
60 #include <linux/srcutiny.h>
61 #elif defined(CONFIG_TREE_SRCU)
62 #include <linux/srcutree.h>
63 #elif defined(CONFIG_SRCU)
64 #error "Unknown SRCU implementation specified to kernel configuration"
65 #else
66 /* Dummy definition for things like notifiers. Actual use gets link error. */
67 struct srcu_struct { };
68 #endif
69
70 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
71 void (*func)(struct rcu_head *head));
72 void cleanup_srcu_struct(struct srcu_struct *sp);
73 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
74 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
75 void synchronize_srcu(struct srcu_struct *sp);
76
77 #ifdef CONFIG_DEBUG_LOCK_ALLOC
78
79 /**
80 * srcu_read_lock_held - might we be in SRCU read-side critical section?
81 * @sp: The srcu_struct structure to check
82 *
83 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
84 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
85 * this assumes we are in an SRCU read-side critical section unless it can
86 * prove otherwise.
87 *
88 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
89 * and while lockdep is disabled.
90 *
91 * Note that SRCU is based on its own statemachine and it doesn't
92 * relies on normal RCU, it can be called from the CPU which
93 * is in the idle loop from an RCU point of view or offline.
94 */
srcu_read_lock_held(struct srcu_struct * sp)95 static inline int srcu_read_lock_held(struct srcu_struct *sp)
96 {
97 if (!debug_lockdep_rcu_enabled())
98 return 1;
99 return lock_is_held(&sp->dep_map);
100 }
101
102 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
103
srcu_read_lock_held(struct srcu_struct * sp)104 static inline int srcu_read_lock_held(struct srcu_struct *sp)
105 {
106 return 1;
107 }
108
109 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
110
111 /**
112 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
113 * @p: the pointer to fetch and protect for later dereferencing
114 * @sp: pointer to the srcu_struct, which is used to check that we
115 * really are in an SRCU read-side critical section.
116 * @c: condition to check for update-side use
117 *
118 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
119 * critical section will result in an RCU-lockdep splat, unless @c evaluates
120 * to 1. The @c argument will normally be a logical expression containing
121 * lockdep_is_held() calls.
122 */
123 #define srcu_dereference_check(p, sp, c) \
124 __rcu_dereference_check((p), (c) || srcu_read_lock_held(sp), __rcu)
125
126 /**
127 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
128 * @p: the pointer to fetch and protect for later dereferencing
129 * @sp: pointer to the srcu_struct, which is used to check that we
130 * really are in an SRCU read-side critical section.
131 *
132 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
133 * is enabled, invoking this outside of an RCU read-side critical
134 * section will result in an RCU-lockdep splat.
135 */
136 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
137
138 /**
139 * srcu_read_lock - register a new reader for an SRCU-protected structure.
140 * @sp: srcu_struct in which to register the new reader.
141 *
142 * Enter an SRCU read-side critical section. Note that SRCU read-side
143 * critical sections may be nested. However, it is illegal to
144 * call anything that waits on an SRCU grace period for the same
145 * srcu_struct, whether directly or indirectly. Please note that
146 * one way to indirectly wait on an SRCU grace period is to acquire
147 * a mutex that is held elsewhere while calling synchronize_srcu() or
148 * synchronize_srcu_expedited().
149 *
150 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
151 * occur in the same context, for example, it is illegal to invoke
152 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
153 * was invoked in process context.
154 */
srcu_read_lock(struct srcu_struct * sp)155 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
156 {
157 int retval;
158
159 retval = __srcu_read_lock(sp);
160 rcu_lock_acquire(&(sp)->dep_map);
161 return retval;
162 }
163
164 /**
165 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
166 * @sp: srcu_struct in which to unregister the old reader.
167 * @idx: return value from corresponding srcu_read_lock().
168 *
169 * Exit an SRCU read-side critical section.
170 */
srcu_read_unlock(struct srcu_struct * sp,int idx)171 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
172 __releases(sp)
173 {
174 rcu_lock_release(&(sp)->dep_map);
175 __srcu_read_unlock(sp, idx);
176 }
177
178 /**
179 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
180 *
181 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
182 *
183 * Call this after srcu_read_unlock, to guarantee that all memory operations
184 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
185 * the preceding srcu_read_unlock.
186 */
smp_mb__after_srcu_read_unlock(void)187 static inline void smp_mb__after_srcu_read_unlock(void)
188 {
189 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
190 }
191
192 #endif
193