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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Paul E. McKenneya71fca52009-09-18 10:28:19 -07002 * Read-Copy Update mechanism for mutual exclusion
Linus Torvalds1da177e2005-04-16 15:20:36 -07003 *
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 *
Paul E. McKenney01c1c662008-01-25 21:08:24 +010018 * Copyright IBM Corporation, 2001
Linus Torvalds1da177e2005-04-16 15:20:36 -070019 *
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
Paul E. McKenneya71fca52009-09-18 10:28:19 -070021 *
Josh Triplett595182b2006-10-04 02:17:21 -070022 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
Linus Torvalds1da177e2005-04-16 15:20:36 -070023 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
24 * Papers:
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
27 *
28 * For detailed explanation of Read-Copy Update mechanism see -
Paul E. McKenneya71fca52009-09-18 10:28:19 -070029 * http://lse.sourceforge.net/locking/rcupdate.html
Linus Torvalds1da177e2005-04-16 15:20:36 -070030 *
31 */
32
33#ifndef __LINUX_RCUPDATE_H
34#define __LINUX_RCUPDATE_H
35
Linus Torvalds1da177e2005-04-16 15:20:36 -070036#include <linux/cache.h>
37#include <linux/spinlock.h>
38#include <linux/threads.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070039#include <linux/cpumask.h>
40#include <linux/seqlock.h>
Peter Zijlstra851a67b2007-10-11 22:11:12 +020041#include <linux/lockdep.h>
Paul E. McKenney4446a362008-05-12 21:21:05 +020042#include <linux/completion.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070043
44/**
45 * struct rcu_head - callback structure for use with RCU
46 * @next: next update requests in a list
47 * @func: actual update function to call after the grace period.
48 */
49struct rcu_head {
50 struct rcu_head *next;
51 void (*func)(struct rcu_head *head);
52};
53
Paul E. McKenney03b042b2009-06-25 09:08:16 -070054/* Exported common interfaces */
Paul E. McKenney16e30812009-09-13 09:15:11 -070055#ifdef CONFIG_TREE_PREEMPT_RCU
Paul E. McKenney03b042b2009-06-25 09:08:16 -070056extern void synchronize_rcu(void);
Paul E. McKenney16e30812009-09-13 09:15:11 -070057#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
58#define synchronize_rcu synchronize_sched
59#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
Paul E. McKenney03b042b2009-06-25 09:08:16 -070060extern void synchronize_rcu_bh(void);
Paul E. McKenney16e30812009-09-13 09:15:11 -070061extern void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -070062extern void rcu_barrier(void);
63extern void rcu_barrier_bh(void);
64extern void rcu_barrier_sched(void);
65extern void synchronize_sched_expedited(void);
66extern int sched_expedited_torture_stats(char *page);
67
68/* Internal to kernel */
69extern void rcu_init(void);
70extern void rcu_scheduler_starting(void);
71extern int rcu_needs_cpu(int cpu);
Paul E. McKenneya6826042009-02-25 18:03:42 -080072extern int rcu_scheduler_active;
73
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070074#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010075#include <linux/rcutree.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010076#else
77#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -070078#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +010079
Dipankar Sarma8b6490e2005-09-09 13:04:07 -070080#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
81#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
Linus Torvalds1da177e2005-04-16 15:20:36 -070082#define INIT_RCU_HEAD(ptr) do { \
83 (ptr)->next = NULL; (ptr)->func = NULL; \
84} while (0)
85
Paul E. McKenneybc33f242009-08-22 13:56:47 -070086#ifdef CONFIG_DEBUG_LOCK_ALLOC
87extern struct lockdep_map rcu_lock_map;
88# define rcu_read_acquire() \
89 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
90# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
91#else
92# define rcu_read_acquire() do { } while (0)
93# define rcu_read_release() do { } while (0)
94#endif
95
Linus Torvalds1da177e2005-04-16 15:20:36 -070096/**
97 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
98 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -070099 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700101 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
103 * on one CPU while other CPUs are within RCU read-side critical
104 * sections, invocation of the corresponding RCU callback is deferred
105 * until after the all the other CPUs exit their critical sections.
106 *
107 * Note, however, that RCU callbacks are permitted to run concurrently
108 * with RCU read-side critical sections. One way that this can happen
109 * is via the following sequence of events: (1) CPU 0 enters an RCU
110 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
111 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
112 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
113 * callback is invoked. This is legal, because the RCU read-side critical
114 * section that was running concurrently with the call_rcu() (and which
115 * therefore might be referencing something that the corresponding RCU
116 * callback would free up) has completed before the corresponding
117 * RCU callback is invoked.
118 *
119 * RCU read-side critical sections may be nested. Any deferred actions
120 * will be deferred until the outermost RCU read-side critical section
121 * completes.
122 *
123 * It is illegal to block while in an RCU read-side critical section.
124 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700125static inline void rcu_read_lock(void)
126{
127 __rcu_read_lock();
128 __acquire(RCU);
129 rcu_read_acquire();
130}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700131
132/**
133 * rcu_read_unlock - marks the end of an RCU read-side critical section.
134 *
135 * See rcu_read_lock() for more information.
136 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700137
138/*
139 * So where is rcu_write_lock()? It does not exist, as there is no
140 * way for writers to lock out RCU readers. This is a feature, not
141 * a bug -- this property is what provides RCU's performance benefits.
142 * Of course, writers must coordinate with each other. The normal
143 * spinlock primitives work well for this, but any other technique may be
144 * used as well. RCU does not care how the writers keep out of each
145 * others' way, as long as they do so.
146 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700147static inline void rcu_read_unlock(void)
148{
149 rcu_read_release();
150 __release(RCU);
151 __rcu_read_unlock();
152}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154/**
155 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
156 *
157 * This is equivalent of rcu_read_lock(), but to be used when updates
158 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
159 * consider completion of a softirq handler to be a quiescent state,
160 * a process in RCU read-side critical section must be protected by
161 * disabling softirqs. Read-side critical sections in interrupt context
162 * can use just rcu_read_lock().
163 *
164 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700165static inline void rcu_read_lock_bh(void)
166{
167 __rcu_read_lock_bh();
168 __acquire(RCU_BH);
169 rcu_read_acquire();
170}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
172/*
173 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
174 *
175 * See rcu_read_lock_bh() for more information.
176 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700177static inline void rcu_read_unlock_bh(void)
178{
179 rcu_read_release();
180 __release(RCU_BH);
181 __rcu_read_unlock_bh();
182}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183
184/**
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400185 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
186 *
187 * Should be used with either
188 * - synchronize_sched()
189 * or
190 * - call_rcu_sched() and rcu_barrier_sched()
191 * on the write-side to insure proper synchronization.
192 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700193static inline void rcu_read_lock_sched(void)
194{
195 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700196 __acquire(RCU_SCHED);
197 rcu_read_acquire();
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700198}
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700199static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700200{
201 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700202 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700203}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400204
205/*
206 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
207 *
208 * See rcu_read_lock_sched for more information.
209 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700210static inline void rcu_read_unlock_sched(void)
211{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700212 rcu_read_release();
213 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700214 preempt_enable();
215}
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700216static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700217{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700218 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700219 preempt_enable_notrace();
220}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400221
222
223/**
Linus Torvalds1da177e2005-04-16 15:20:36 -0700224 * rcu_dereference - fetch an RCU-protected pointer in an
225 * RCU read-side critical section. This pointer may later
226 * be safely dereferenced.
227 *
228 * Inserts memory barriers on architectures that require them
229 * (currently only the Alpha), and, more importantly, documents
230 * exactly which pointers are protected by RCU.
231 */
232
233#define rcu_dereference(p) ({ \
Paul E. McKenney97b43032007-10-16 23:26:04 -0700234 typeof(p) _________p1 = ACCESS_ONCE(p); \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700235 smp_read_barrier_depends(); \
236 (_________p1); \
237 })
238
239/**
240 * rcu_assign_pointer - assign (publicize) a pointer to a newly
241 * initialized structure that will be dereferenced by RCU read-side
242 * critical sections. Returns the value assigned.
243 *
244 * Inserts memory barriers on architectures that require them
245 * (pretty much all of them other than x86), and also prevents
246 * the compiler from reordering the code that initializes the
247 * structure after the pointer assignment. More importantly, this
248 * call documents which pointers will be dereferenced by RCU read-side
249 * code.
250 */
251
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800252#define rcu_assign_pointer(p, v) \
253 ({ \
254 if (!__builtin_constant_p(v) || \
255 ((v) != NULL)) \
256 smp_wmb(); \
257 (p) = (v); \
258 })
Linus Torvalds1da177e2005-04-16 15:20:36 -0700259
Paul E. McKenney4446a362008-05-12 21:21:05 +0200260/* Infrastructure to implement the synchronize_() primitives. */
261
262struct rcu_synchronize {
263 struct rcu_head head;
264 struct completion completion;
265};
266
267extern void wakeme_after_rcu(struct rcu_head *head);
268
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700269/**
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100270 * call_rcu - Queue an RCU callback for invocation after a grace period.
271 * @head: structure to be used for queueing the RCU updates.
272 * @func: actual update function to be invoked after the grace period
273 *
274 * The update function will be invoked some time after a full grace
275 * period elapses, in other words after all currently executing RCU
276 * read-side critical sections have completed. RCU read-side critical
277 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
278 * and may be nested.
279 */
280extern void call_rcu(struct rcu_head *head,
281 void (*func)(struct rcu_head *head));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700282
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100283/**
284 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
285 * @head: structure to be used for queueing the RCU updates.
286 * @func: actual update function to be invoked after the grace period
287 *
288 * The update function will be invoked some time after a full grace
289 * period elapses, in other words after all currently executing RCU
290 * read-side critical sections have completed. call_rcu_bh() assumes
291 * that the read-side critical sections end on completion of a softirq
292 * handler. This means that read-side critical sections in process
293 * context must not be interrupted by softirqs. This interface is to be
294 * used when most of the read-side critical sections are in softirq context.
295 * RCU read-side critical sections are delimited by :
296 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
297 * OR
298 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
299 * These may be nested.
300 */
301extern void call_rcu_bh(struct rcu_head *head,
302 void (*func)(struct rcu_head *head));
303
Linus Torvalds1da177e2005-04-16 15:20:36 -0700304#endif /* __LINUX_RCUPDATE_H */