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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#include <linux/completion.h>
44
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
55#ifdef CONFIG_CLASSIC_RCU
56#include <linux/rcuclassic.h>
57#else /* #ifdef CONFIG_CLASSIC_RCU */
58#include <linux/rcupreempt.h>
59#endif /* #else #ifdef CONFIG_CLASSIC_RCU */
60
61#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
62#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
63#define INIT_RCU_HEAD(ptr) do { \
64 (ptr)->next = NULL; (ptr)->func = NULL; \
65} while (0)
66
67/**
68 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
69 *
70 * When synchronize_rcu() is invoked on one CPU while other CPUs
71 * are within RCU read-side critical sections, then the
72 * synchronize_rcu() is guaranteed to block until after all the other
73 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
74 * on one CPU while other CPUs are within RCU read-side critical
75 * sections, invocation of the corresponding RCU callback is deferred
76 * until after the all the other CPUs exit their critical sections.
77 *
78 * Note, however, that RCU callbacks are permitted to run concurrently
79 * with RCU read-side critical sections. One way that this can happen
80 * is via the following sequence of events: (1) CPU 0 enters an RCU
81 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
82 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
83 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
84 * callback is invoked. This is legal, because the RCU read-side critical
85 * section that was running concurrently with the call_rcu() (and which
86 * therefore might be referencing something that the corresponding RCU
87 * callback would free up) has completed before the corresponding
88 * RCU callback is invoked.
89 *
90 * RCU read-side critical sections may be nested. Any deferred actions
91 * will be deferred until the outermost RCU read-side critical section
92 * completes.
93 *
94 * It is illegal to block while in an RCU read-side critical section.
95 */
96#define rcu_read_lock() __rcu_read_lock()
97
98/**
99 * rcu_read_unlock - marks the end of an RCU read-side critical section.
100 *
101 * See rcu_read_lock() for more information.
102 */
103
104/*
105 * So where is rcu_write_lock()? It does not exist, as there is no
106 * way for writers to lock out RCU readers. This is a feature, not
107 * a bug -- this property is what provides RCU's performance benefits.
108 * Of course, writers must coordinate with each other. The normal
109 * spinlock primitives work well for this, but any other technique may be
110 * used as well. RCU does not care how the writers keep out of each
111 * others' way, as long as they do so.
112 */
113#define rcu_read_unlock() __rcu_read_unlock()
114
115/**
116 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
117 *
118 * This is equivalent of rcu_read_lock(), but to be used when updates
119 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
120 * consider completion of a softirq handler to be a quiescent state,
121 * a process in RCU read-side critical section must be protected by
122 * disabling softirqs. Read-side critical sections in interrupt context
123 * can use just rcu_read_lock().
124 *
125 */
126#define rcu_read_lock_bh() __rcu_read_lock_bh()
127
128/*
129 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
130 *
131 * See rcu_read_lock_bh() for more information.
132 */
133#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
134
135/**
136 * rcu_dereference - fetch an RCU-protected pointer in an
137 * RCU read-side critical section. This pointer may later
138 * be safely dereferenced.
139 *
140 * Inserts memory barriers on architectures that require them
141 * (currently only the Alpha), and, more importantly, documents
142 * exactly which pointers are protected by RCU.
143 */
144
145#define rcu_dereference(p) ({ \
146 typeof(p) _________p1 = ACCESS_ONCE(p); \
147 smp_read_barrier_depends(); \
148 (_________p1); \
149 })
150
151/**
152 * rcu_assign_pointer - assign (publicize) a pointer to a newly
153 * initialized structure that will be dereferenced by RCU read-side
154 * critical sections. Returns the value assigned.
155 *
156 * Inserts memory barriers on architectures that require them
157 * (pretty much all of them other than x86), and also prevents
158 * the compiler from reordering the code that initializes the
159 * structure after the pointer assignment. More importantly, this
160 * call documents which pointers will be dereferenced by RCU read-side
161 * code.
162 */
163
164#define rcu_assign_pointer(p, v) \
165 ({ \
166 if (!__builtin_constant_p(v) || \
167 ((v) != NULL)) \
168 smp_wmb(); \
169 (p) = (v); \
170 })
171
172/* Infrastructure to implement the synchronize_() primitives. */
173
174struct rcu_synchronize {
175 struct rcu_head head;
176 struct completion completion;
177};
178
179extern void wakeme_after_rcu(struct rcu_head *head);
180
181#define synchronize_rcu_xxx(name, func) \
182void name(void) \
183{ \
184 struct rcu_synchronize rcu; \
185 \
186 init_completion(&rcu.completion); \
187 /* Will wake me after RCU finished. */ \
188 func(&rcu.head, wakeme_after_rcu); \
189 /* Wait for it. */ \
190 wait_for_completion(&rcu.completion); \
191}
192
193/**
194 * synchronize_sched - block until all CPUs have exited any non-preemptive
195 * kernel code sequences.
196 *
197 * This means that all preempt_disable code sequences, including NMI and
198 * hardware-interrupt handlers, in progress on entry will have completed
199 * before this primitive returns. However, this does not guarantee that
200 * softirq handlers will have completed, since in some kernels, these
201 * handlers can run in process context, and can block.
202 *
203 * This primitive provides the guarantees made by the (now removed)
204 * synchronize_kernel() API. In contrast, synchronize_rcu() only
205 * guarantees that rcu_read_lock() sections will have completed.
206 * In "classic RCU", these two guarantees happen to be one and
207 * the same, but can differ in realtime RCU implementations.
208 */
209#define synchronize_sched() __synchronize_sched()
210
211/**
212 * call_rcu - Queue an RCU callback for invocation after a grace period.
213 * @head: structure to be used for queueing the RCU updates.
214 * @func: actual update function to be invoked after the grace period
215 *
216 * The update function will be invoked some time after a full grace
217 * period elapses, in other words after all currently executing RCU
218 * read-side critical sections have completed. RCU read-side critical
219 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
220 * and may be nested.
221 */
222extern void call_rcu(struct rcu_head *head,
223 void (*func)(struct rcu_head *head));
224
225/**
226 * call_rcu_bh - Queue an RCU for invocation after a quicker 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. call_rcu_bh() assumes
233 * that the read-side critical sections end on completion of a softirq
234 * handler. This means that read-side critical sections in process
235 * context must not be interrupted by softirqs. This interface is to be
236 * used when most of the read-side critical sections are in softirq context.
237 * RCU read-side critical sections are delimited by :
238 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
239 * OR
240 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
241 * These may be nested.
242 */
243extern void call_rcu_bh(struct rcu_head *head,
244 void (*func)(struct rcu_head *head));
245
246/* Exported common interfaces */
247extern void synchronize_rcu(void);
248extern void rcu_barrier(void);
249extern void rcu_barrier_bh(void);
250extern void rcu_barrier_sched(void);
251
252/* Internal to kernel */
253extern void rcu_init(void);
254extern int rcu_needs_cpu(int cpu);
255
256#endif /* __LINUX_RCUPDATE_H */