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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#include <linux/rcupdate.h>
32
33struct srcu_struct_array {
34 int c[2];
35};
36
37struct srcu_struct {
38 int completed;
39 struct srcu_struct_array __percpu *per_cpu_ref;
40 struct mutex mutex;
41#ifdef CONFIG_DEBUG_LOCK_ALLOC
42 struct lockdep_map dep_map;
43#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
44};
45
46#ifndef CONFIG_PREEMPT
47#define srcu_barrier() barrier()
48#else /* #ifndef CONFIG_PREEMPT */
49#define srcu_barrier()
50#endif /* #else #ifndef CONFIG_PREEMPT */
51
52#ifdef CONFIG_DEBUG_LOCK_ALLOC
53
54int __init_srcu_struct(struct srcu_struct *sp, const char *name,
55 struct lock_class_key *key);
56
57#define init_srcu_struct(sp) \
58({ \
59 static struct lock_class_key __srcu_key; \
60 \
61 __init_srcu_struct((sp), #sp, &__srcu_key); \
62})
63
64#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
65
66int init_srcu_struct(struct srcu_struct *sp);
67
68#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
69
70void cleanup_srcu_struct(struct srcu_struct *sp);
71int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
72void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
73void synchronize_srcu(struct srcu_struct *sp);
74void synchronize_srcu_expedited(struct srcu_struct *sp);
75long srcu_batches_completed(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 *
82 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
83 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
84 * this assumes we are in an SRCU read-side critical section unless it can
85 * prove otherwise.
86 *
87 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
88 * and while lockdep is disabled.
89 *
90 * Note that if the CPU is in the idle loop from an RCU point of view
91 * (ie: that we are in the section between rcu_idle_enter() and
92 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
93 * the CPU did an srcu_read_lock(). The reason for this is that RCU
94 * ignores CPUs that are in such a section, considering these as in
95 * extended quiescent state, so such a CPU is effectively never in an
96 * RCU read-side critical section regardless of what RCU primitives it
97 * invokes. This state of affairs is required --- we need to keep an
98 * RCU-free window in idle where the CPU may possibly enter into low
99 * power mode. This way we can notice an extended quiescent state to
100 * other CPUs that started a grace period. Otherwise we would delay any
101 * grace period as long as we run in the idle task.
102 *
103 * Similarly, we avoid claiming an SRCU read lock held if the current
104 * CPU is offline.
105 */
106static inline int srcu_read_lock_held(struct srcu_struct *sp)
107{
108 if (!debug_lockdep_rcu_enabled())
109 return 1;
110 if (rcu_is_cpu_idle())
111 return 0;
112 if (!rcu_lockdep_current_cpu_online())
113 return 0;
114 return lock_is_held(&sp->dep_map);
115}
116
117#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
118
119static inline int srcu_read_lock_held(struct srcu_struct *sp)
120{
121 return 1;
122}
123
124#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
125
126/**
127 * srcu_dereference_check - 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 * @c: condition to check for update-side use
132 *
133 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
134 * critical section will result in an RCU-lockdep splat, unless @c evaluates
135 * to 1. The @c argument will normally be a logical expression containing
136 * lockdep_is_held() calls.
137 */
138#define srcu_dereference_check(p, sp, c) \
139 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
140
141/**
142 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
143 * @p: the pointer to fetch and protect for later dereferencing
144 * @sp: pointer to the srcu_struct, which is used to check that we
145 * really are in an SRCU read-side critical section.
146 *
147 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
148 * is enabled, invoking this outside of an RCU read-side critical
149 * section will result in an RCU-lockdep splat.
150 */
151#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
152
153/**
154 * srcu_read_lock - register a new reader for an SRCU-protected structure.
155 * @sp: srcu_struct in which to register the new reader.
156 *
157 * Enter an SRCU read-side critical section. Note that SRCU read-side
158 * critical sections may be nested. However, it is illegal to
159 * call anything that waits on an SRCU grace period for the same
160 * srcu_struct, whether directly or indirectly. Please note that
161 * one way to indirectly wait on an SRCU grace period is to acquire
162 * a mutex that is held elsewhere while calling synchronize_srcu() or
163 * synchronize_srcu_expedited().
164 *
165 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
166 * occur in the same context, for example, it is illegal to invoke
167 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
168 * was invoked in process context.
169 */
170static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
171{
172 int retval = __srcu_read_lock(sp);
173
174 rcu_lock_acquire(&(sp)->dep_map);
175 rcu_lockdep_assert(!rcu_is_cpu_idle(),
176 "srcu_read_lock() used illegally while idle");
177 return retval;
178}
179
180/**
181 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
182 * @sp: srcu_struct in which to unregister the old reader.
183 * @idx: return value from corresponding srcu_read_lock().
184 *
185 * Exit an SRCU read-side critical section.
186 */
187static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
188 __releases(sp)
189{
190 rcu_lockdep_assert(!rcu_is_cpu_idle(),
191 "srcu_read_unlock() used illegally while idle");
192 rcu_lock_release(&(sp)->dep_map);
193 __srcu_read_unlock(sp, idx);
194}
195
196/**
197 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
198 * @sp: srcu_struct in which to register the new reader.
199 *
200 * Enter an SRCU read-side critical section. Similar to srcu_read_lock(),
201 * but avoids the RCU-lockdep checking. This means that it is legal to
202 * use srcu_read_lock_raw() in one context, for example, in an exception
203 * handler, and then have the matching srcu_read_unlock_raw() in another
204 * context, for example in the task that took the exception.
205 *
206 * However, the entire SRCU read-side critical section must reside within a
207 * single task. For example, beware of using srcu_read_lock_raw() in
208 * a device interrupt handler and srcu_read_unlock() in the interrupted
209 * task: This will not work if interrupts are threaded.
210 */
211static inline int srcu_read_lock_raw(struct srcu_struct *sp)
212{
213 unsigned long flags;
214 int ret;
215
216 local_irq_save(flags);
217 ret = __srcu_read_lock(sp);
218 local_irq_restore(flags);
219 return ret;
220}
221
222/**
223 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
224 * @sp: srcu_struct in which to unregister the old reader.
225 * @idx: return value from corresponding srcu_read_lock_raw().
226 *
227 * Exit an SRCU read-side critical section without lockdep-RCU checking.
228 * See srcu_read_lock_raw() for more details.
229 */
230static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
231{
232 unsigned long flags;
233
234 local_irq_save(flags);
235 __srcu_read_unlock(sp, idx);
236 local_irq_restore(flags);
237}
238
239#endif