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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/* Exported common interfaces */
55extern void synchronize_rcu_bh(void);
56extern void synchronize_sched(void);
57extern void rcu_barrier(void);
58extern void rcu_barrier_bh(void);
59extern void rcu_barrier_sched(void);
60extern void synchronize_sched_expedited(void);
61extern int sched_expedited_torture_stats(char *page);
62
63/* Internal to kernel */
64extern void rcu_init(void);
65
66#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
67#include <linux/rcutree.h>
68#elif defined(CONFIG_TINY_RCU)
69#include <linux/rcutiny.h>
70#else
71#error "Unknown RCU implementation specified to kernel configuration"
72#endif
73
74#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
75#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
76#define INIT_RCU_HEAD(ptr) do { \
77 (ptr)->next = NULL; (ptr)->func = NULL; \
78} while (0)
79
80#ifdef CONFIG_DEBUG_LOCK_ALLOC
81extern struct lockdep_map rcu_lock_map;
82# define rcu_read_acquire() \
83 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
84# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
85#else
86# define rcu_read_acquire() do { } while (0)
87# define rcu_read_release() do { } while (0)
88#endif
89
90/**
91 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
92 *
93 * When synchronize_rcu() is invoked on one CPU while other CPUs
94 * are within RCU read-side critical sections, then the
95 * synchronize_rcu() is guaranteed to block until after all the other
96 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
97 * on one CPU while other CPUs are within RCU read-side critical
98 * sections, invocation of the corresponding RCU callback is deferred
99 * until after the all the other CPUs exit their critical sections.
100 *
101 * Note, however, that RCU callbacks are permitted to run concurrently
102 * with RCU read-side critical sections. One way that this can happen
103 * is via the following sequence of events: (1) CPU 0 enters an RCU
104 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
105 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
106 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
107 * callback is invoked. This is legal, because the RCU read-side critical
108 * section that was running concurrently with the call_rcu() (and which
109 * therefore might be referencing something that the corresponding RCU
110 * callback would free up) has completed before the corresponding
111 * RCU callback is invoked.
112 *
113 * RCU read-side critical sections may be nested. Any deferred actions
114 * will be deferred until the outermost RCU read-side critical section
115 * completes.
116 *
117 * It is illegal to block while in an RCU read-side critical section.
118 */
119static inline void rcu_read_lock(void)
120{
121 __rcu_read_lock();
122 __acquire(RCU);
123 rcu_read_acquire();
124}
125
126/*
127 * So where is rcu_write_lock()? It does not exist, as there is no
128 * way for writers to lock out RCU readers. This is a feature, not
129 * a bug -- this property is what provides RCU's performance benefits.
130 * Of course, writers must coordinate with each other. The normal
131 * spinlock primitives work well for this, but any other technique may be
132 * used as well. RCU does not care how the writers keep out of each
133 * others' way, as long as they do so.
134 */
135
136/**
137 * rcu_read_unlock - marks the end of an RCU read-side critical section.
138 *
139 * See rcu_read_lock() for more information.
140 */
141static inline void rcu_read_unlock(void)
142{
143 rcu_read_release();
144 __release(RCU);
145 __rcu_read_unlock();
146}
147
148/**
149 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
150 *
151 * This is equivalent of rcu_read_lock(), but to be used when updates
152 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
153 * consider completion of a softirq handler to be a quiescent state,
154 * a process in RCU read-side critical section must be protected by
155 * disabling softirqs. Read-side critical sections in interrupt context
156 * can use just rcu_read_lock().
157 *
158 */
159static inline void rcu_read_lock_bh(void)
160{
161 __rcu_read_lock_bh();
162 __acquire(RCU_BH);
163 rcu_read_acquire();
164}
165
166/*
167 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
168 *
169 * See rcu_read_lock_bh() for more information.
170 */
171static inline void rcu_read_unlock_bh(void)
172{
173 rcu_read_release();
174 __release(RCU_BH);
175 __rcu_read_unlock_bh();
176}
177
178/**
179 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
180 *
181 * Should be used with either
182 * - synchronize_sched()
183 * or
184 * - call_rcu_sched() and rcu_barrier_sched()
185 * on the write-side to insure proper synchronization.
186 */
187static inline void rcu_read_lock_sched(void)
188{
189 preempt_disable();
190 __acquire(RCU_SCHED);
191 rcu_read_acquire();
192}
193
194/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
195static inline notrace void rcu_read_lock_sched_notrace(void)
196{
197 preempt_disable_notrace();
198 __acquire(RCU_SCHED);
199}
200
201/*
202 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
203 *
204 * See rcu_read_lock_sched for more information.
205 */
206static inline void rcu_read_unlock_sched(void)
207{
208 rcu_read_release();
209 __release(RCU_SCHED);
210 preempt_enable();
211}
212
213/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
214static inline notrace void rcu_read_unlock_sched_notrace(void)
215{
216 __release(RCU_SCHED);
217 preempt_enable_notrace();
218}
219
220
221/**
222 * rcu_dereference - fetch an RCU-protected pointer in an
223 * RCU read-side critical section. This pointer may later
224 * be safely dereferenced.
225 *
226 * Inserts memory barriers on architectures that require them
227 * (currently only the Alpha), and, more importantly, documents
228 * exactly which pointers are protected by RCU.
229 */
230
231#define rcu_dereference(p) ({ \
232 typeof(p) _________p1 = ACCESS_ONCE(p); \
233 smp_read_barrier_depends(); \
234 (_________p1); \
235 })
236
237/**
238 * rcu_assign_pointer - assign (publicize) a pointer to a newly
239 * initialized structure that will be dereferenced by RCU read-side
240 * critical sections. Returns the value assigned.
241 *
242 * Inserts memory barriers on architectures that require them
243 * (pretty much all of them other than x86), and also prevents
244 * the compiler from reordering the code that initializes the
245 * structure after the pointer assignment. More importantly, this
246 * call documents which pointers will be dereferenced by RCU read-side
247 * code.
248 */
249
250#define rcu_assign_pointer(p, v) \
251 ({ \
252 if (!__builtin_constant_p(v) || \
253 ((v) != NULL)) \
254 smp_wmb(); \
255 (p) = (v); \
256 })
257
258/* Infrastructure to implement the synchronize_() primitives. */
259
260struct rcu_synchronize {
261 struct rcu_head head;
262 struct completion completion;
263};
264
265extern void wakeme_after_rcu(struct rcu_head *head);
266
267/**
268 * call_rcu - Queue an RCU callback for invocation after a grace period.
269 * @head: structure to be used for queueing the RCU updates.
270 * @func: actual update function to be invoked after the grace period
271 *
272 * The update function will be invoked some time after a full grace
273 * period elapses, in other words after all currently executing RCU
274 * read-side critical sections have completed. RCU read-side critical
275 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
276 * and may be nested.
277 */
278extern void call_rcu(struct rcu_head *head,
279 void (*func)(struct rcu_head *head));
280
281/**
282 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
283 * @head: structure to be used for queueing the RCU updates.
284 * @func: actual update function to be invoked after the grace period
285 *
286 * The update function will be invoked some time after a full grace
287 * period elapses, in other words after all currently executing RCU
288 * read-side critical sections have completed. call_rcu_bh() assumes
289 * that the read-side critical sections end on completion of a softirq
290 * handler. This means that read-side critical sections in process
291 * context must not be interrupted by softirqs. This interface is to be
292 * used when most of the read-side critical sections are in softirq context.
293 * RCU read-side critical sections are delimited by :
294 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
295 * OR
296 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
297 * These may be nested.
298 */
299extern void call_rcu_bh(struct rcu_head *head,
300 void (*func)(struct rcu_head *head));
301
302#endif /* __LINUX_RCUPDATE_H */