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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/cpumask.h>
40#include <linux/seqlock.h>
41#include <linux/lockdep.h>
42#include <linux/completion.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/* Internal to kernel, but needed by rcupreempt.h. */
55extern int rcu_scheduler_active;
56
57#if defined(CONFIG_CLASSIC_RCU)
58#include <linux/rcuclassic.h>
59#elif defined(CONFIG_TREE_RCU)
60#include <linux/rcutree.h>
61#elif defined(CONFIG_PREEMPT_RCU)
62#include <linux/rcupreempt.h>
63#else
64#error "Unknown RCU implementation specified to kernel configuration"
65#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
66
67#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
68#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
69#define INIT_RCU_HEAD(ptr) do { \
70 (ptr)->next = NULL; (ptr)->func = NULL; \
71} while (0)
72
73/**
74 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
75 *
76 * When synchronize_rcu() is invoked on one CPU while other CPUs
77 * are within RCU read-side critical sections, then the
78 * synchronize_rcu() is guaranteed to block until after all the other
79 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
80 * on one CPU while other CPUs are within RCU read-side critical
81 * sections, invocation of the corresponding RCU callback is deferred
82 * until after the all the other CPUs exit their critical sections.
83 *
84 * Note, however, that RCU callbacks are permitted to run concurrently
85 * with RCU read-side critical sections. One way that this can happen
86 * is via the following sequence of events: (1) CPU 0 enters an RCU
87 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
88 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
89 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
90 * callback is invoked. This is legal, because the RCU read-side critical
91 * section that was running concurrently with the call_rcu() (and which
92 * therefore might be referencing something that the corresponding RCU
93 * callback would free up) has completed before the corresponding
94 * RCU callback is invoked.
95 *
96 * RCU read-side critical sections may be nested. Any deferred actions
97 * will be deferred until the outermost RCU read-side critical section
98 * completes.
99 *
100 * It is illegal to block while in an RCU read-side critical section.
101 */
102#define rcu_read_lock() __rcu_read_lock()
103
104/**
105 * rcu_read_unlock - marks the end of an RCU read-side critical section.
106 *
107 * See rcu_read_lock() for more information.
108 */
109
110/*
111 * So where is rcu_write_lock()? It does not exist, as there is no
112 * way for writers to lock out RCU readers. This is a feature, not
113 * a bug -- this property is what provides RCU's performance benefits.
114 * Of course, writers must coordinate with each other. The normal
115 * spinlock primitives work well for this, but any other technique may be
116 * used as well. RCU does not care how the writers keep out of each
117 * others' way, as long as they do so.
118 */
119#define rcu_read_unlock() __rcu_read_unlock()
120
121/**
122 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
123 *
124 * This is equivalent of rcu_read_lock(), but to be used when updates
125 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
126 * consider completion of a softirq handler to be a quiescent state,
127 * a process in RCU read-side critical section must be protected by
128 * disabling softirqs. Read-side critical sections in interrupt context
129 * can use just rcu_read_lock().
130 *
131 */
132#define rcu_read_lock_bh() __rcu_read_lock_bh()
133
134/*
135 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
136 *
137 * See rcu_read_lock_bh() for more information.
138 */
139#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
140
141/**
142 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
143 *
144 * Should be used with either
145 * - synchronize_sched()
146 * or
147 * - call_rcu_sched() and rcu_barrier_sched()
148 * on the write-side to insure proper synchronization.
149 */
150#define rcu_read_lock_sched() preempt_disable()
151#define rcu_read_lock_sched_notrace() preempt_disable_notrace()
152
153/*
154 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
155 *
156 * See rcu_read_lock_sched for more information.
157 */
158#define rcu_read_unlock_sched() preempt_enable()
159#define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
160
161
162
163/**
164 * rcu_dereference - fetch an RCU-protected pointer in an
165 * RCU read-side critical section. This pointer may later
166 * be safely dereferenced.
167 *
168 * Inserts memory barriers on architectures that require them
169 * (currently only the Alpha), and, more importantly, documents
170 * exactly which pointers are protected by RCU.
171 */
172
173#define rcu_dereference(p) ({ \
174 typeof(p) _________p1 = ACCESS_ONCE(p); \
175 smp_read_barrier_depends(); \
176 (_________p1); \
177 })
178
179/**
180 * rcu_assign_pointer - assign (publicize) a pointer to a newly
181 * initialized structure that will be dereferenced by RCU read-side
182 * critical sections. Returns the value assigned.
183 *
184 * Inserts memory barriers on architectures that require them
185 * (pretty much all of them other than x86), and also prevents
186 * the compiler from reordering the code that initializes the
187 * structure after the pointer assignment. More importantly, this
188 * call documents which pointers will be dereferenced by RCU read-side
189 * code.
190 */
191
192#define rcu_assign_pointer(p, v) \
193 ({ \
194 if (!__builtin_constant_p(v) || \
195 ((v) != NULL)) \
196 smp_wmb(); \
197 (p) = (v); \
198 })
199
200/* Infrastructure to implement the synchronize_() primitives. */
201
202struct rcu_synchronize {
203 struct rcu_head head;
204 struct completion completion;
205};
206
207extern void wakeme_after_rcu(struct rcu_head *head);
208
209/**
210 * synchronize_sched - block until all CPUs have exited any non-preemptive
211 * kernel code sequences.
212 *
213 * This means that all preempt_disable code sequences, including NMI and
214 * hardware-interrupt handlers, in progress on entry will have completed
215 * before this primitive returns. However, this does not guarantee that
216 * softirq handlers will have completed, since in some kernels, these
217 * handlers can run in process context, and can block.
218 *
219 * This primitive provides the guarantees made by the (now removed)
220 * synchronize_kernel() API. In contrast, synchronize_rcu() only
221 * guarantees that rcu_read_lock() sections will have completed.
222 * In "classic RCU", these two guarantees happen to be one and
223 * the same, but can differ in realtime RCU implementations.
224 */
225#define synchronize_sched() __synchronize_sched()
226
227/**
228 * call_rcu - Queue an RCU callback for invocation after a grace period.
229 * @head: structure to be used for queueing the RCU updates.
230 * @func: actual update function to be invoked after the grace period
231 *
232 * The update function will be invoked some time after a full grace
233 * period elapses, in other words after all currently executing RCU
234 * read-side critical sections have completed. RCU read-side critical
235 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
236 * and may be nested.
237 */
238extern void call_rcu(struct rcu_head *head,
239 void (*func)(struct rcu_head *head));
240
241/**
242 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
243 * @head: structure to be used for queueing the RCU updates.
244 * @func: actual update function to be invoked after the grace period
245 *
246 * The update function will be invoked some time after a full grace
247 * period elapses, in other words after all currently executing RCU
248 * read-side critical sections have completed. call_rcu_bh() assumes
249 * that the read-side critical sections end on completion of a softirq
250 * handler. This means that read-side critical sections in process
251 * context must not be interrupted by softirqs. This interface is to be
252 * used when most of the read-side critical sections are in softirq context.
253 * RCU read-side critical sections are delimited by :
254 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
255 * OR
256 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
257 * These may be nested.
258 */
259extern void call_rcu_bh(struct rcu_head *head,
260 void (*func)(struct rcu_head *head));
261
262/* Exported common interfaces */
263extern void synchronize_rcu(void);
264extern void rcu_barrier(void);
265extern void rcu_barrier_bh(void);
266extern void rcu_barrier_sched(void);
267
268/* Internal to kernel */
269extern void rcu_init(void);
270extern void rcu_scheduler_starting(void);
271extern int rcu_needs_cpu(int cpu);
272
273#endif /* __LINUX_RCUPDATE_H */