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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 * 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
36struct srcu_struct_array {
37 unsigned long c[2];
38 unsigned long seq[2];
39};
40
41struct rcu_batch {
42 struct rcu_head *head, **tail;
43};
44
45#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
46
47struct srcu_struct {
48 unsigned completed;
49 struct srcu_struct_array __percpu *per_cpu_ref;
50 spinlock_t queue_lock; /* protect ->batch_queue, ->running */
51 bool running;
52 /* callbacks just queued */
53 struct rcu_batch batch_queue;
54 /* callbacks try to do the first check_zero */
55 struct rcu_batch batch_check0;
56 /* callbacks done with the first check_zero and the flip */
57 struct rcu_batch batch_check1;
58 struct rcu_batch batch_done;
59 struct delayed_work work;
60#ifdef CONFIG_DEBUG_LOCK_ALLOC
61 struct lockdep_map dep_map;
62#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
63};
64
65#ifdef CONFIG_DEBUG_LOCK_ALLOC
66
67int __init_srcu_struct(struct srcu_struct *sp, const char *name,
68 struct lock_class_key *key);
69
70#define init_srcu_struct(sp) \
71({ \
72 static struct lock_class_key __srcu_key; \
73 \
74 __init_srcu_struct((sp), #sp, &__srcu_key); \
75})
76
77#define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
78#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
79
80int init_srcu_struct(struct srcu_struct *sp);
81
82#define __SRCU_DEP_MAP_INIT(srcu_name)
83#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
84
85void process_srcu(struct work_struct *work);
86
87#define __SRCU_STRUCT_INIT(name) \
88 { \
89 .completed = -300, \
90 .per_cpu_ref = &name##_srcu_array, \
91 .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
92 .running = false, \
93 .batch_queue = RCU_BATCH_INIT(name.batch_queue), \
94 .batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
95 .batch_check1 = RCU_BATCH_INIT(name.batch_check1), \
96 .batch_done = RCU_BATCH_INIT(name.batch_done), \
97 .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
98 __SRCU_DEP_MAP_INIT(name) \
99 }
100
101/*
102 * define and init a srcu struct at build time.
103 * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
104 */
105#define DEFINE_SRCU(name) \
106 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
107 struct srcu_struct name = __SRCU_STRUCT_INIT(name);
108
109#define DEFINE_STATIC_SRCU(name) \
110 static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
111 static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
112
113/**
114 * call_srcu() - Queue a callback for invocation after an SRCU grace period
115 * @sp: srcu_struct in queue the callback
116 * @head: structure to be used for queueing the SRCU callback.
117 * @func: function to be invoked after the SRCU grace period
118 *
119 * The callback function will be invoked some time after a full SRCU
120 * grace period elapses, in other words after all pre-existing SRCU
121 * read-side critical sections have completed. However, the callback
122 * function might well execute concurrently with other SRCU read-side
123 * critical sections that started after call_srcu() was invoked. SRCU
124 * read-side critical sections are delimited by srcu_read_lock() and
125 * srcu_read_unlock(), and may be nested.
126 *
127 * The callback will be invoked from process context, but must nevertheless
128 * be fast and must not block.
129 */
130void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
131 void (*func)(struct rcu_head *head));
132
133void cleanup_srcu_struct(struct srcu_struct *sp);
134int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
135void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
136void synchronize_srcu(struct srcu_struct *sp);
137void synchronize_srcu_expedited(struct srcu_struct *sp);
138long srcu_batches_completed(struct srcu_struct *sp);
139void srcu_barrier(struct srcu_struct *sp);
140
141#ifdef CONFIG_DEBUG_LOCK_ALLOC
142
143/**
144 * srcu_read_lock_held - might we be in SRCU read-side critical section?
145 *
146 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
147 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
148 * this assumes we are in an SRCU read-side critical section unless it can
149 * prove otherwise.
150 *
151 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
152 * and while lockdep is disabled.
153 *
154 * Note that if the CPU is in the idle loop from an RCU point of view
155 * (ie: that we are in the section between rcu_idle_enter() and
156 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
157 * the CPU did an srcu_read_lock(). The reason for this is that RCU
158 * ignores CPUs that are in such a section, considering these as in
159 * extended quiescent state, so such a CPU is effectively never in an
160 * RCU read-side critical section regardless of what RCU primitives it
161 * invokes. This state of affairs is required --- we need to keep an
162 * RCU-free window in idle where the CPU may possibly enter into low
163 * power mode. This way we can notice an extended quiescent state to
164 * other CPUs that started a grace period. Otherwise we would delay any
165 * grace period as long as we run in the idle task.
166 *
167 * Similarly, we avoid claiming an SRCU read lock held if the current
168 * CPU is offline.
169 */
170static inline int srcu_read_lock_held(struct srcu_struct *sp)
171{
172 if (!debug_lockdep_rcu_enabled())
173 return 1;
174 if (rcu_is_cpu_idle())
175 return 0;
176 if (!rcu_lockdep_current_cpu_online())
177 return 0;
178 return lock_is_held(&sp->dep_map);
179}
180
181#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
182
183static inline int srcu_read_lock_held(struct srcu_struct *sp)
184{
185 return 1;
186}
187
188#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
189
190/**
191 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
192 * @p: the pointer to fetch and protect for later dereferencing
193 * @sp: pointer to the srcu_struct, which is used to check that we
194 * really are in an SRCU read-side critical section.
195 * @c: condition to check for update-side use
196 *
197 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
198 * critical section will result in an RCU-lockdep splat, unless @c evaluates
199 * to 1. The @c argument will normally be a logical expression containing
200 * lockdep_is_held() calls.
201 */
202#define srcu_dereference_check(p, sp, c) \
203 __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
204
205/**
206 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
207 * @p: the pointer to fetch and protect for later dereferencing
208 * @sp: pointer to the srcu_struct, which is used to check that we
209 * really are in an SRCU read-side critical section.
210 *
211 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
212 * is enabled, invoking this outside of an RCU read-side critical
213 * section will result in an RCU-lockdep splat.
214 */
215#define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
216
217/**
218 * srcu_read_lock - register a new reader for an SRCU-protected structure.
219 * @sp: srcu_struct in which to register the new reader.
220 *
221 * Enter an SRCU read-side critical section. Note that SRCU read-side
222 * critical sections may be nested. However, it is illegal to
223 * call anything that waits on an SRCU grace period for the same
224 * srcu_struct, whether directly or indirectly. Please note that
225 * one way to indirectly wait on an SRCU grace period is to acquire
226 * a mutex that is held elsewhere while calling synchronize_srcu() or
227 * synchronize_srcu_expedited().
228 *
229 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
230 * occur in the same context, for example, it is illegal to invoke
231 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
232 * was invoked in process context.
233 */
234static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
235{
236 int retval = __srcu_read_lock(sp);
237
238 rcu_lock_acquire(&(sp)->dep_map);
239 rcu_lockdep_assert(!rcu_is_cpu_idle(),
240 "srcu_read_lock() used illegally while idle");
241 return retval;
242}
243
244/**
245 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
246 * @sp: srcu_struct in which to unregister the old reader.
247 * @idx: return value from corresponding srcu_read_lock().
248 *
249 * Exit an SRCU read-side critical section.
250 */
251static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
252 __releases(sp)
253{
254 rcu_lockdep_assert(!rcu_is_cpu_idle(),
255 "srcu_read_unlock() used illegally while idle");
256 rcu_lock_release(&(sp)->dep_map);
257 __srcu_read_unlock(sp, idx);
258}
259
260/**
261 * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
262 * @sp: srcu_struct in which to register the new reader.
263 *
264 * Enter an SRCU read-side critical section. Similar to srcu_read_lock(),
265 * but avoids the RCU-lockdep checking. This means that it is legal to
266 * use srcu_read_lock_raw() in one context, for example, in an exception
267 * handler, and then have the matching srcu_read_unlock_raw() in another
268 * context, for example in the task that took the exception.
269 *
270 * However, the entire SRCU read-side critical section must reside within a
271 * single task. For example, beware of using srcu_read_lock_raw() in
272 * a device interrupt handler and srcu_read_unlock() in the interrupted
273 * task: This will not work if interrupts are threaded.
274 */
275static inline int srcu_read_lock_raw(struct srcu_struct *sp)
276{
277 unsigned long flags;
278 int ret;
279
280 local_irq_save(flags);
281 ret = __srcu_read_lock(sp);
282 local_irq_restore(flags);
283 return ret;
284}
285
286/**
287 * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
288 * @sp: srcu_struct in which to unregister the old reader.
289 * @idx: return value from corresponding srcu_read_lock_raw().
290 *
291 * Exit an SRCU read-side critical section without lockdep-RCU checking.
292 * See srcu_read_lock_raw() for more details.
293 */
294static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
295{
296 unsigned long flags;
297
298 local_irq_save(flags);
299 __srcu_read_unlock(sp, idx);
300 local_irq_restore(flags);
301}
302
303#endif