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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. McKenneya6826042009-02-25 18:03:42 -080055/* Internal to kernel, but needed by rcupreempt.h. */
56extern int rcu_scheduler_active;
57
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010058#if defined(CONFIG_CLASSIC_RCU)
Paul E. McKenney01c1c662008-01-25 21:08:24 +010059#include <linux/rcuclassic.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010060#elif defined(CONFIG_TREE_RCU)
61#include <linux/rcutree.h>
62#elif defined(CONFIG_PREEMPT_RCU)
Paul E. McKenneye260be62008-01-25 21:08:24 +010063#include <linux/rcupreempt.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +010064#else
65#error "Unknown RCU implementation specified to kernel configuration"
66#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
Paul E. McKenney01c1c662008-01-25 21:08:24 +010067
Dipankar Sarma8b6490e2005-09-09 13:04:07 -070068#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
69#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
Linus Torvalds1da177e2005-04-16 15:20:36 -070070#define INIT_RCU_HEAD(ptr) do { \
71 (ptr)->next = NULL; (ptr)->func = NULL; \
72} while (0)
73
Linus Torvalds1da177e2005-04-16 15:20:36 -070074/**
75 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
76 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -070077 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -070078 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -070079 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -070080 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
81 * on one CPU while other CPUs are within RCU read-side critical
82 * sections, invocation of the corresponding RCU callback is deferred
83 * until after the all the other CPUs exit their critical sections.
84 *
85 * Note, however, that RCU callbacks are permitted to run concurrently
86 * with RCU read-side critical sections. One way that this can happen
87 * is via the following sequence of events: (1) CPU 0 enters an RCU
88 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
89 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
90 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
91 * callback is invoked. This is legal, because the RCU read-side critical
92 * section that was running concurrently with the call_rcu() (and which
93 * therefore might be referencing something that the corresponding RCU
94 * callback would free up) has completed before the corresponding
95 * RCU callback is invoked.
96 *
97 * RCU read-side critical sections may be nested. Any deferred actions
98 * will be deferred until the outermost RCU read-side critical section
99 * completes.
100 *
101 * It is illegal to block while in an RCU read-side critical section.
102 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100103#define rcu_read_lock() __rcu_read_lock()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104
105/**
106 * rcu_read_unlock - marks the end of an RCU read-side critical section.
107 *
108 * See rcu_read_lock() for more information.
109 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110
111/*
112 * So where is rcu_write_lock()? It does not exist, as there is no
113 * way for writers to lock out RCU readers. This is a feature, not
114 * a bug -- this property is what provides RCU's performance benefits.
115 * Of course, writers must coordinate with each other. The normal
116 * spinlock primitives work well for this, but any other technique may be
117 * used as well. RCU does not care how the writers keep out of each
118 * others' way, as long as they do so.
119 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100120#define rcu_read_unlock() __rcu_read_unlock()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121
122/**
123 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
124 *
125 * This is equivalent of rcu_read_lock(), but to be used when updates
126 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
127 * consider completion of a softirq handler to be a quiescent state,
128 * a process in RCU read-side critical section must be protected by
129 * disabling softirqs. Read-side critical sections in interrupt context
130 * can use just rcu_read_lock().
131 *
132 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100133#define rcu_read_lock_bh() __rcu_read_lock_bh()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700134
135/*
136 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
137 *
138 * See rcu_read_lock_bh() for more information.
139 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100140#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
Linus Torvalds1da177e2005-04-16 15:20:36 -0700141
142/**
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400143 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
144 *
145 * Should be used with either
146 * - synchronize_sched()
147 * or
148 * - call_rcu_sched() and rcu_barrier_sched()
149 * on the write-side to insure proper synchronization.
150 */
151#define rcu_read_lock_sched() preempt_disable()
Mathieu Desnoyers954e1002008-11-14 17:47:34 -0500152#define rcu_read_lock_sched_notrace() preempt_disable_notrace()
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400153
154/*
155 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
156 *
157 * See rcu_read_lock_sched for more information.
158 */
159#define rcu_read_unlock_sched() preempt_enable()
Mathieu Desnoyers954e1002008-11-14 17:47:34 -0500160#define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400161
162
163
164/**
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 * rcu_dereference - fetch an RCU-protected pointer in an
166 * RCU read-side critical section. This pointer may later
167 * be safely dereferenced.
168 *
169 * Inserts memory barriers on architectures that require them
170 * (currently only the Alpha), and, more importantly, documents
171 * exactly which pointers are protected by RCU.
172 */
173
174#define rcu_dereference(p) ({ \
Paul E. McKenney97b43032007-10-16 23:26:04 -0700175 typeof(p) _________p1 = ACCESS_ONCE(p); \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700176 smp_read_barrier_depends(); \
177 (_________p1); \
178 })
179
180/**
181 * rcu_assign_pointer - assign (publicize) a pointer to a newly
182 * initialized structure that will be dereferenced by RCU read-side
183 * critical sections. Returns the value assigned.
184 *
185 * Inserts memory barriers on architectures that require them
186 * (pretty much all of them other than x86), and also prevents
187 * the compiler from reordering the code that initializes the
188 * structure after the pointer assignment. More importantly, this
189 * call documents which pointers will be dereferenced by RCU read-side
190 * code.
191 */
192
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800193#define rcu_assign_pointer(p, v) \
194 ({ \
195 if (!__builtin_constant_p(v) || \
196 ((v) != NULL)) \
197 smp_wmb(); \
198 (p) = (v); \
199 })
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200
Paul E. McKenney4446a362008-05-12 21:21:05 +0200201/* Infrastructure to implement the synchronize_() primitives. */
202
203struct rcu_synchronize {
204 struct rcu_head head;
205 struct completion completion;
206};
207
208extern void wakeme_after_rcu(struct rcu_head *head);
209
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700210/**
211 * synchronize_sched - block until all CPUs have exited any non-preemptive
212 * kernel code sequences.
213 *
214 * This means that all preempt_disable code sequences, including NMI and
215 * hardware-interrupt handlers, in progress on entry will have completed
216 * before this primitive returns. However, this does not guarantee that
Paul E. McKenneybb3b9cf12006-02-03 03:04:38 -0800217 * softirq handlers will have completed, since in some kernels, these
218 * handlers can run in process context, and can block.
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700219 *
Paul E. McKenneyd83015b2006-06-23 02:05:51 -0700220 * This primitive provides the guarantees made by the (now removed)
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700221 * synchronize_kernel() API. In contrast, synchronize_rcu() only
222 * guarantees that rcu_read_lock() sections will have completed.
Paul E. McKenneybb3b9cf12006-02-03 03:04:38 -0800223 * In "classic RCU", these two guarantees happen to be one and
224 * the same, but can differ in realtime RCU implementations.
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700225 */
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100226#define synchronize_sched() __synchronize_sched()
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700227
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100228/**
229 * call_rcu - Queue an RCU callback for invocation after a grace period.
230 * @head: structure to be used for queueing the RCU updates.
231 * @func: actual update function to be invoked after the grace period
232 *
233 * The update function will be invoked some time after a full grace
234 * period elapses, in other words after all currently executing RCU
235 * read-side critical sections have completed. RCU read-side critical
236 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
237 * and may be nested.
238 */
239extern void call_rcu(struct rcu_head *head,
240 void (*func)(struct rcu_head *head));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100242/**
243 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
244 * @head: structure to be used for queueing the RCU updates.
245 * @func: actual update function to be invoked after the grace period
246 *
247 * The update function will be invoked some time after a full grace
248 * period elapses, in other words after all currently executing RCU
249 * read-side critical sections have completed. call_rcu_bh() assumes
250 * that the read-side critical sections end on completion of a softirq
251 * handler. This means that read-side critical sections in process
252 * context must not be interrupted by softirqs. This interface is to be
253 * used when most of the read-side critical sections are in softirq context.
254 * RCU read-side critical sections are delimited by :
255 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
256 * OR
257 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
258 * These may be nested.
259 */
260extern void call_rcu_bh(struct rcu_head *head,
261 void (*func)(struct rcu_head *head));
262
263/* Exported common interfaces */
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700264extern void synchronize_rcu(void);
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800265extern void rcu_barrier(void);
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200266extern void rcu_barrier_bh(void);
267extern void rcu_barrier_sched(void);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700268
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100269/* Internal to kernel */
270extern void rcu_init(void);
Paul E. McKenneya6826042009-02-25 18:03:42 -0800271extern void rcu_scheduler_starting(void);
Paul E. McKenneye260be62008-01-25 21:08:24 +0100272extern int rcu_needs_cpu(int cpu);
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100273
Linus Torvalds1da177e2005-04-16 15:20:36 -0700274#endif /* __LINUX_RCUPDATE_H */