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1/*
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 *
18 * Copyright IBM Corporation, 2001
19 *
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
21 *
22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
23 * 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
36#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>
42#include <linux/lockdep.h>
43
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
54#ifdef CONFIG_CLASSIC_RCU
55#include <linux/rcuclassic.h>
56#else /* #ifdef CONFIG_CLASSIC_RCU */
57#include <linux/rcupreempt.h>
58#endif /* #else #ifdef CONFIG_CLASSIC_RCU */
59
60#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
61#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
62#define INIT_RCU_HEAD(ptr) do { \
63 (ptr)->next = NULL; (ptr)->func = NULL; \
64} while (0)
65
66/**
67 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
68 *
69 * When synchronize_rcu() is invoked on one CPU while other CPUs
70 * are within RCU read-side critical sections, then the
71 * synchronize_rcu() is guaranteed to block until after all the other
72 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
73 * on one CPU while other CPUs are within RCU read-side critical
74 * sections, invocation of the corresponding RCU callback is deferred
75 * until after the all the other CPUs exit their critical sections.
76 *
77 * Note, however, that RCU callbacks are permitted to run concurrently
78 * with RCU read-side critical sections. One way that this can happen
79 * is via the following sequence of events: (1) CPU 0 enters an RCU
80 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
81 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
82 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
83 * callback is invoked. This is legal, because the RCU read-side critical
84 * section that was running concurrently with the call_rcu() (and which
85 * therefore might be referencing something that the corresponding RCU
86 * callback would free up) has completed before the corresponding
87 * RCU callback is invoked.
88 *
89 * RCU read-side critical sections may be nested. Any deferred actions
90 * will be deferred until the outermost RCU read-side critical section
91 * completes.
92 *
93 * It is illegal to block while in an RCU read-side critical section.
94 */
95#define rcu_read_lock() __rcu_read_lock()
96
97/**
98 * rcu_read_unlock - marks the end of an RCU read-side critical section.
99 *
100 * See rcu_read_lock() for more information.
101 */
102
103/*
104 * So where is rcu_write_lock()? It does not exist, as there is no
105 * way for writers to lock out RCU readers. This is a feature, not
106 * a bug -- this property is what provides RCU's performance benefits.
107 * Of course, writers must coordinate with each other. The normal
108 * spinlock primitives work well for this, but any other technique may be
109 * used as well. RCU does not care how the writers keep out of each
110 * others' way, as long as they do so.
111 */
112#define rcu_read_unlock() __rcu_read_unlock()
113
114/**
115 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
116 *
117 * This is equivalent of rcu_read_lock(), but to be used when updates
118 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
119 * consider completion of a softirq handler to be a quiescent state,
120 * a process in RCU read-side critical section must be protected by
121 * disabling softirqs. Read-side critical sections in interrupt context
122 * can use just rcu_read_lock().
123 *
124 */
125#define rcu_read_lock_bh() __rcu_read_lock_bh()
126
127/*
128 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
129 *
130 * See rcu_read_lock_bh() for more information.
131 */
132#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
133
134/**
135 * rcu_dereference - fetch an RCU-protected pointer in an
136 * RCU read-side critical section. This pointer may later
137 * be safely dereferenced.
138 *
139 * Inserts memory barriers on architectures that require them
140 * (currently only the Alpha), and, more importantly, documents
141 * exactly which pointers are protected by RCU.
142 */
143
144#define rcu_dereference(p) ({ \
145 typeof(p) _________p1 = ACCESS_ONCE(p); \
146 smp_read_barrier_depends(); \
147 (_________p1); \
148 })
149
150/**
151 * rcu_assign_pointer - assign (publicize) a pointer to a newly
152 * initialized structure that will be dereferenced by RCU read-side
153 * critical sections. Returns the value assigned.
154 *
155 * Inserts memory barriers on architectures that require them
156 * (pretty much all of them other than x86), and also prevents
157 * the compiler from reordering the code that initializes the
158 * structure after the pointer assignment. More importantly, this
159 * call documents which pointers will be dereferenced by RCU read-side
160 * code.
161 */
162
163#define rcu_assign_pointer(p, v) \
164 ({ \
165 if (!__builtin_constant_p(v) || \
166 ((v) != NULL)) \
167 smp_wmb(); \
168 (p) = (v); \
169 })
170
171/**
172 * synchronize_sched - block until all CPUs have exited any non-preemptive
173 * kernel code sequences.
174 *
175 * This means that all preempt_disable code sequences, including NMI and
176 * hardware-interrupt handlers, in progress on entry will have completed
177 * before this primitive returns. However, this does not guarantee that
178 * softirq handlers will have completed, since in some kernels, these
179 * handlers can run in process context, and can block.
180 *
181 * This primitive provides the guarantees made by the (now removed)
182 * synchronize_kernel() API. In contrast, synchronize_rcu() only
183 * guarantees that rcu_read_lock() sections will have completed.
184 * In "classic RCU", these two guarantees happen to be one and
185 * the same, but can differ in realtime RCU implementations.
186 */
187#define synchronize_sched() __synchronize_sched()
188
189/**
190 * call_rcu - Queue an RCU callback for invocation after a grace period.
191 * @head: structure to be used for queueing the RCU updates.
192 * @func: actual update function to be invoked after the grace period
193 *
194 * The update function will be invoked some time after a full grace
195 * period elapses, in other words after all currently executing RCU
196 * read-side critical sections have completed. RCU read-side critical
197 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
198 * and may be nested.
199 */
200extern void call_rcu(struct rcu_head *head,
201 void (*func)(struct rcu_head *head));
202
203/**
204 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
205 * @head: structure to be used for queueing the RCU updates.
206 * @func: actual update function to be invoked after the grace period
207 *
208 * The update function will be invoked some time after a full grace
209 * period elapses, in other words after all currently executing RCU
210 * read-side critical sections have completed. call_rcu_bh() assumes
211 * that the read-side critical sections end on completion of a softirq
212 * handler. This means that read-side critical sections in process
213 * context must not be interrupted by softirqs. This interface is to be
214 * used when most of the read-side critical sections are in softirq context.
215 * RCU read-side critical sections are delimited by :
216 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
217 * OR
218 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
219 * These may be nested.
220 */
221extern void call_rcu_bh(struct rcu_head *head,
222 void (*func)(struct rcu_head *head));
223
224/* Exported common interfaces */
225extern void synchronize_rcu(void);
226extern void rcu_barrier(void);
227extern long rcu_batches_completed(void);
228extern long rcu_batches_completed_bh(void);
229
230/* Internal to kernel */
231extern void rcu_init(void);
232extern int rcu_needs_cpu(int cpu);
233
234#endif /* __LINUX_RCUPDATE_H */