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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * 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 *
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>
21 *
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 -
29 * http://lse.sourceforge.net/locking/rcupdate.html
30 *
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>
39#include <linux/percpu.h>
40#include <linux/cpumask.h>
41#include <linux/seqlock.h>
Peter Zijlstra851a67b2007-10-11 22:11:12 +020042#include <linux/lockdep.h>
Paul E. McKenney4446a362008-05-12 21:21:05 +020043#include <linux/completion.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070044
45/**
46 * struct rcu_head - callback structure for use with RCU
47 * @next: next update requests in a list
48 * @func: actual update function to call after the grace period.
49 */
50struct rcu_head {
51 struct rcu_head *next;
52 void (*func)(struct rcu_head *head);
53};
54
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010055#if defined(CONFIG_CLASSIC_RCU)
Paul E. McKenney01c1c662008-01-25 21:08:24 +010056#include <linux/rcuclassic.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010057#elif defined(CONFIG_TREE_RCU)
58#include <linux/rcutree.h>
59#elif defined(CONFIG_PREEMPT_RCU)
Paul E. McKenneye260be62008-01-25 21:08:24 +010060#include <linux/rcupreempt.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010061#else
62#error "Unknown RCU implementation specified to kernel configuration"
63#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
Paul E. McKenney01c1c662008-01-25 21:08:24 +010064
Dipankar Sarma8b6490e2005-09-09 13:04:07 -070065#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
66#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
Linus Torvalds1da177e2005-04-16 15:20:36 -070067#define INIT_RCU_HEAD(ptr) do { \
68 (ptr)->next = NULL; (ptr)->func = NULL; \
69} while (0)
70
Linus Torvalds1da177e2005-04-16 15:20:36 -070071/**
72 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
73 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -070074 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -070075 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -070076 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -070077 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
78 * on one CPU while other CPUs are within RCU read-side critical
79 * sections, invocation of the corresponding RCU callback is deferred
80 * until after the all the other CPUs exit their critical sections.
81 *
82 * Note, however, that RCU callbacks are permitted to run concurrently
83 * with RCU read-side critical sections. One way that this can happen
84 * is via the following sequence of events: (1) CPU 0 enters an RCU
85 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
86 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
87 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
88 * callback is invoked. This is legal, because the RCU read-side critical
89 * section that was running concurrently with the call_rcu() (and which
90 * therefore might be referencing something that the corresponding RCU
91 * callback would free up) has completed before the corresponding
92 * RCU callback is invoked.
93 *
94 * RCU read-side critical sections may be nested. Any deferred actions
95 * will be deferred until the outermost RCU read-side critical section
96 * completes.
97 *
98 * It is illegal to block while in an RCU read-side critical section.
99 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100100#define rcu_read_lock() __rcu_read_lock()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101
102/**
103 * rcu_read_unlock - marks the end of an RCU read-side critical section.
104 *
105 * See rcu_read_lock() for more information.
106 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107
108/*
109 * So where is rcu_write_lock()? It does not exist, as there is no
110 * way for writers to lock out RCU readers. This is a feature, not
111 * a bug -- this property is what provides RCU's performance benefits.
112 * Of course, writers must coordinate with each other. The normal
113 * spinlock primitives work well for this, but any other technique may be
114 * used as well. RCU does not care how the writers keep out of each
115 * others' way, as long as they do so.
116 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100117#define rcu_read_unlock() __rcu_read_unlock()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118
119/**
120 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
121 *
122 * This is equivalent of rcu_read_lock(), but to be used when updates
123 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
124 * consider completion of a softirq handler to be a quiescent state,
125 * a process in RCU read-side critical section must be protected by
126 * disabling softirqs. Read-side critical sections in interrupt context
127 * can use just rcu_read_lock().
128 *
129 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100130#define rcu_read_lock_bh() __rcu_read_lock_bh()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700131
132/*
133 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
134 *
135 * See rcu_read_lock_bh() for more information.
136 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100137#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
139/**
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400140 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
141 *
142 * Should be used with either
143 * - synchronize_sched()
144 * or
145 * - call_rcu_sched() and rcu_barrier_sched()
146 * on the write-side to insure proper synchronization.
147 */
148#define rcu_read_lock_sched() preempt_disable()
Mathieu Desnoyers954e1002008-11-14 17:47:34 -0500149#define rcu_read_lock_sched_notrace() preempt_disable_notrace()
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400150
151/*
152 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
153 *
154 * See rcu_read_lock_sched for more information.
155 */
156#define rcu_read_unlock_sched() preempt_enable()
Mathieu Desnoyers954e1002008-11-14 17:47:34 -0500157#define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400158
159
160
161/**
Linus Torvalds1da177e2005-04-16 15:20:36 -0700162 * rcu_dereference - fetch an RCU-protected pointer in an
163 * RCU read-side critical section. This pointer may later
164 * be safely dereferenced.
165 *
166 * Inserts memory barriers on architectures that require them
167 * (currently only the Alpha), and, more importantly, documents
168 * exactly which pointers are protected by RCU.
169 */
170
171#define rcu_dereference(p) ({ \
Paul E. McKenney97b43032007-10-16 23:26:04 -0700172 typeof(p) _________p1 = ACCESS_ONCE(p); \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700173 smp_read_barrier_depends(); \
174 (_________p1); \
175 })
176
177/**
178 * rcu_assign_pointer - assign (publicize) a pointer to a newly
179 * initialized structure that will be dereferenced by RCU read-side
180 * critical sections. Returns the value assigned.
181 *
182 * Inserts memory barriers on architectures that require them
183 * (pretty much all of them other than x86), and also prevents
184 * the compiler from reordering the code that initializes the
185 * structure after the pointer assignment. More importantly, this
186 * call documents which pointers will be dereferenced by RCU read-side
187 * code.
188 */
189
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800190#define rcu_assign_pointer(p, v) \
191 ({ \
192 if (!__builtin_constant_p(v) || \
193 ((v) != NULL)) \
194 smp_wmb(); \
195 (p) = (v); \
196 })
Linus Torvalds1da177e2005-04-16 15:20:36 -0700197
Paul E. McKenney4446a362008-05-12 21:21:05 +0200198/* Infrastructure to implement the synchronize_() primitives. */
199
200struct rcu_synchronize {
201 struct rcu_head head;
202 struct completion completion;
203};
204
205extern void wakeme_after_rcu(struct rcu_head *head);
206
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700207/**
208 * synchronize_sched - block until all CPUs have exited any non-preemptive
209 * kernel code sequences.
210 *
211 * This means that all preempt_disable code sequences, including NMI and
212 * hardware-interrupt handlers, in progress on entry will have completed
213 * before this primitive returns. However, this does not guarantee that
Paul E. McKenneybb3b9cf2006-02-03 03:04:38 -0800214 * softirq handlers will have completed, since in some kernels, these
215 * handlers can run in process context, and can block.
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700216 *
Paul E. McKenneyd83015b2006-06-23 02:05:51 -0700217 * This primitive provides the guarantees made by the (now removed)
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700218 * synchronize_kernel() API. In contrast, synchronize_rcu() only
219 * guarantees that rcu_read_lock() sections will have completed.
Paul E. McKenneybb3b9cf2006-02-03 03:04:38 -0800220 * In "classic RCU", these two guarantees happen to be one and
221 * the same, but can differ in realtime RCU implementations.
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700222 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100223#define synchronize_sched() __synchronize_sched()
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700224
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100225/**
226 * call_rcu - Queue an RCU callback for invocation after a grace period.
227 * @head: structure to be used for queueing the RCU updates.
228 * @func: actual update function to be invoked after the grace period
229 *
230 * The update function will be invoked some time after a full grace
231 * period elapses, in other words after all currently executing RCU
232 * read-side critical sections have completed. RCU read-side critical
233 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
234 * and may be nested.
235 */
236extern void call_rcu(struct rcu_head *head,
237 void (*func)(struct rcu_head *head));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700238
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100239/**
240 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
241 * @head: structure to be used for queueing the RCU updates.
242 * @func: actual update function to be invoked after the grace period
243 *
244 * The update function will be invoked some time after a full grace
245 * period elapses, in other words after all currently executing RCU
246 * read-side critical sections have completed. call_rcu_bh() assumes
247 * that the read-side critical sections end on completion of a softirq
248 * handler. This means that read-side critical sections in process
249 * context must not be interrupted by softirqs. This interface is to be
250 * used when most of the read-side critical sections are in softirq context.
251 * RCU read-side critical sections are delimited by :
252 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
253 * OR
254 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
255 * These may be nested.
256 */
257extern void call_rcu_bh(struct rcu_head *head,
258 void (*func)(struct rcu_head *head));
259
260/* Exported common interfaces */
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700261extern void synchronize_rcu(void);
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800262extern void rcu_barrier(void);
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200263extern void rcu_barrier_bh(void);
264extern void rcu_barrier_sched(void);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700265
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100266/* Internal to kernel */
267extern void rcu_init(void);
Paul E. McKenneye260be62008-01-25 21:08:24 +0100268extern int rcu_needs_cpu(int cpu);
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100269
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270#endif /* __LINUX_RCUPDATE_H */