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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Paul E. McKenneya71fca52009-09-18 10:28:19 -07002 * Read-Copy Update mechanism for mutual exclusion
Linus Torvalds1da177e2005-04-16 15:20:36 -07003 *
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
Paul E. McKenney87de1cf2013-12-03 10:02:52 -080015 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
Linus Torvalds1da177e2005-04-16 15:20:36 -070017 *
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>
Paul E. McKenneya71fca52009-09-18 10:28:19 -070021 *
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 -
Paul E. McKenneya71fca52009-09-18 10:28:19 -070029 * http://lse.sourceforge.net/locking/rcupdate.html
Linus Torvalds1da177e2005-04-16 15:20:36 -070030 *
31 */
32
33#ifndef __LINUX_RCUPDATE_H
34#define __LINUX_RCUPDATE_H
35
Paul E. McKenney99098752011-05-31 21:03:55 -070036#include <linux/types.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070037#include <linux/cache.h>
38#include <linux/spinlock.h>
39#include <linux/threads.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070040#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>
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -040044#include <linux/debugobjects.h>
Paul Gortmaker187f1882011-11-23 20:12:59 -050045#include <linux/bug.h>
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -070046#include <linux/compiler.h>
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +000047#include <linux/ktime.h>
Paul E. McKenney4929c912016-05-02 11:58:56 -070048#include <linux/irqflags.h>
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +000049
Paul E. McKenney88c18632013-12-16 13:24:32 -080050#include <asm/barrier.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070051
Paul E. McKenney79cfea02015-12-07 13:09:52 -080052#ifndef CONFIG_TINY_RCU
Paul Gortmaker7a754742014-02-11 16:10:12 -050053extern int rcu_expedited; /* for sysctl */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080054extern int rcu_normal; /* also for sysctl */
Paul E. McKenney79cfea02015-12-07 13:09:52 -080055#endif /* #ifndef CONFIG_TINY_RCU */
Dave Younge5ab6772010-03-10 15:24:05 -080056
Paul E. McKenney0d394822015-02-18 12:24:30 -080057#ifdef CONFIG_TINY_RCU
58/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080059static inline bool rcu_gp_is_normal(void) /* Internal RCU use. */
60{
61 return true;
62}
Paul E. McKenney0d394822015-02-18 12:24:30 -080063static inline bool rcu_gp_is_expedited(void) /* Internal RCU use. */
64{
65 return false;
66}
67
68static inline void rcu_expedite_gp(void)
69{
70}
71
72static inline void rcu_unexpedite_gp(void)
73{
74}
75#else /* #ifdef CONFIG_TINY_RCU */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080076bool rcu_gp_is_normal(void); /* Internal RCU use. */
Paul E. McKenney0d394822015-02-18 12:24:30 -080077bool rcu_gp_is_expedited(void); /* Internal RCU use. */
78void rcu_expedite_gp(void);
79void rcu_unexpedite_gp(void);
80#endif /* #else #ifdef CONFIG_TINY_RCU */
81
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080082enum rcutorture_type {
83 RCU_FLAVOR,
84 RCU_BH_FLAVOR,
85 RCU_SCHED_FLAVOR,
Paul E. McKenney69c60452014-07-01 11:59:36 -070086 RCU_TASKS_FLAVOR,
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080087 SRCU_FLAVOR,
88 INVALID_RCU_FLAVOR
89};
90
Pranith Kumar28f65692014-09-22 14:00:48 -040091#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080092void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
93 unsigned long *gpnum, unsigned long *completed);
Teodora Baluta584dc4c2013-11-11 17:11:23 +020094void rcutorture_record_test_transition(void);
95void rcutorture_record_progress(unsigned long vernum);
96void do_trace_rcu_torture_read(const char *rcutorturename,
97 struct rcu_head *rhp,
98 unsigned long secs,
99 unsigned long c_old,
100 unsigned long c);
Paul E. McKenney4a298652011-04-03 21:33:51 -0700101#else
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -0800102static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
103 int *flags,
104 unsigned long *gpnum,
105 unsigned long *completed)
106{
107 *flags = 0;
108 *gpnum = 0;
109 *completed = 0;
110}
Paul E. McKenney4a298652011-04-03 21:33:51 -0700111static inline void rcutorture_record_test_transition(void)
112{
113}
114static inline void rcutorture_record_progress(unsigned long vernum)
115{
116}
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700117#ifdef CONFIG_RCU_TRACE
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200118void do_trace_rcu_torture_read(const char *rcutorturename,
119 struct rcu_head *rhp,
120 unsigned long secs,
121 unsigned long c_old,
122 unsigned long c);
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700123#else
Paul E. McKenney52494532012-11-14 16:26:40 -0800124#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
125 do { } while (0)
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700126#endif
Paul E. McKenney4a298652011-04-03 21:33:51 -0700127#endif
128
Tejun Heoe27fc962010-11-22 21:36:11 -0800129#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
130#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700131#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
132#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -0800133#define ulong2long(a) (*(long *)(&(a)))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700134
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700135/* Exported common interfaces */
Paul E. McKenney2c428182011-05-26 22:14:36 -0700136
137#ifdef CONFIG_PREEMPT_RCU
138
139/**
140 * call_rcu() - Queue an RCU callback for invocation after a grace period.
141 * @head: structure to be used for queueing the RCU updates.
142 * @func: actual callback function to be invoked after the grace period
143 *
144 * The callback function will be invoked some time after a full grace
145 * period elapses, in other words after all pre-existing RCU read-side
146 * critical sections have completed. However, the callback function
147 * might well execute concurrently with RCU read-side critical sections
148 * that started after call_rcu() was invoked. RCU read-side critical
149 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
150 * and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700151 *
152 * Note that all CPUs must agree that the grace period extended beyond
153 * all pre-existing RCU read-side critical section. On systems with more
154 * than one CPU, this means that when "func()" is invoked, each CPU is
155 * guaranteed to have executed a full memory barrier since the end of its
156 * last RCU read-side critical section whose beginning preceded the call
157 * to call_rcu(). It also means that each CPU executing an RCU read-side
158 * critical section that continues beyond the start of "func()" must have
159 * executed a memory barrier after the call_rcu() but before the beginning
160 * of that RCU read-side critical section. Note that these guarantees
161 * include CPUs that are offline, idle, or executing in user mode, as
162 * well as CPUs that are executing in the kernel.
163 *
164 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
165 * resulting RCU callback function "func()", then both CPU A and CPU B are
166 * guaranteed to execute a full memory barrier during the time interval
167 * between the call to call_rcu() and the invocation of "func()" -- even
168 * if CPU A and CPU B are the same CPU (but again only if the system has
169 * more than one CPU).
Paul E. McKenney2c428182011-05-26 22:14:36 -0700170 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200171void call_rcu(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800172 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700173
174#else /* #ifdef CONFIG_PREEMPT_RCU */
175
176/* In classic RCU, call_rcu() is just call_rcu_sched(). */
177#define call_rcu call_rcu_sched
178
179#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
180
181/**
182 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
183 * @head: structure to be used for queueing the RCU updates.
184 * @func: actual callback function to be invoked after the grace period
185 *
186 * The callback function will be invoked some time after a full grace
187 * period elapses, in other words after all currently executing RCU
188 * read-side critical sections have completed. call_rcu_bh() assumes
189 * that the read-side critical sections end on completion of a softirq
190 * handler. This means that read-side critical sections in process
191 * context must not be interrupted by softirqs. This interface is to be
192 * used when most of the read-side critical sections are in softirq context.
193 * RCU read-side critical sections are delimited by :
194 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
195 * OR
196 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
197 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700198 *
199 * See the description of call_rcu() for more detailed information on
200 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700201 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200202void call_rcu_bh(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800203 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700204
205/**
206 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
207 * @head: structure to be used for queueing the RCU updates.
208 * @func: actual callback function to be invoked after the grace period
209 *
210 * The callback function will be invoked some time after a full grace
211 * period elapses, in other words after all currently executing RCU
212 * read-side critical sections have completed. call_rcu_sched() assumes
213 * that the read-side critical sections end on enabling of preemption
214 * or on voluntary preemption.
215 * RCU read-side critical sections are delimited by :
216 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
217 * OR
218 * anything that disables preemption.
219 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700220 *
221 * See the description of call_rcu() for more detailed information on
222 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700223 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200224void call_rcu_sched(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800225 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700226
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200227void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700228
Paul E. McKenneyee376db2015-01-10 19:47:10 -0800229/*
230 * Structure allowing asynchronous waiting on RCU.
231 */
232struct rcu_synchronize {
233 struct rcu_head head;
234 struct completion completion;
235};
236void wakeme_after_rcu(struct rcu_head *head);
237
Paul E. McKenneyec90a192015-06-10 12:53:06 -0700238void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
239 struct rcu_synchronize *rs_array);
240
241#define _wait_rcu_gp(checktiny, ...) \
Oleg Nesterov66e8c572015-08-25 20:45:18 +0200242do { \
243 call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
244 struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)]; \
245 __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array), \
246 __crcu_array, __rs_array); \
Paul E. McKenneyec90a192015-06-10 12:53:06 -0700247} while (0)
248
249#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
250
251/**
252 * synchronize_rcu_mult - Wait concurrently for multiple grace periods
253 * @...: List of call_rcu() functions for the flavors to wait on.
254 *
255 * This macro waits concurrently for multiple flavors of RCU grace periods.
256 * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
257 * on concurrent RCU and RCU-bh grace periods. Waiting on a give SRCU
258 * domain requires you to write a wrapper function for that SRCU domain's
259 * call_srcu() function, supplying the corresponding srcu_struct.
260 *
261 * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
262 * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
263 * is automatically a grace period.
264 */
265#define synchronize_rcu_mult(...) \
266 _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
267
Paul E. McKenney8315f422014-06-27 13:42:20 -0700268/**
269 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
270 * @head: structure to be used for queueing the RCU updates.
271 * @func: actual callback function to be invoked after the grace period
272 *
273 * The callback function will be invoked some time after a full grace
274 * period elapses, in other words after all currently executing RCU
275 * read-side critical sections have completed. call_rcu_tasks() assumes
276 * that the read-side critical sections end at a voluntary context
277 * switch (not a preemption!), entry into idle, or transition to usermode
278 * execution. As such, there are no read-side primitives analogous to
279 * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
280 * to determine that all tasks have passed through a safe state, not so
281 * much for data-strcuture synchronization.
282 *
283 * See the description of call_rcu() for more detailed information on
284 * memory ordering guarantees.
285 */
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800286void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
Paul E. McKenney53c6d4e2014-07-01 12:22:23 -0700287void synchronize_rcu_tasks(void);
288void rcu_barrier_tasks(void);
Paul E. McKenney8315f422014-06-27 13:42:20 -0700289
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700290#ifdef CONFIG_PREEMPT_RCU
291
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200292void __rcu_read_lock(void);
293void __rcu_read_unlock(void);
294void rcu_read_unlock_special(struct task_struct *t);
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700295void synchronize_rcu(void);
296
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700297/*
298 * Defined as a macro as it is a very low level header included from
299 * areas that don't even know about current. This gives the rcu_read_lock()
300 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
301 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
302 */
303#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
304
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700305#else /* #ifdef CONFIG_PREEMPT_RCU */
306
307static inline void __rcu_read_lock(void)
308{
Boqun Fengbb73c522015-07-30 16:55:38 -0700309 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
310 preempt_disable();
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700311}
312
313static inline void __rcu_read_unlock(void)
314{
Boqun Fengbb73c522015-07-30 16:55:38 -0700315 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
316 preempt_enable();
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700317}
318
319static inline void synchronize_rcu(void)
320{
321 synchronize_sched();
322}
323
324static inline int rcu_preempt_depth(void)
325{
326 return 0;
327}
328
329#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
330
331/* Internal to kernel */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200332void rcu_init(void);
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700333void rcu_sched_qs(void);
334void rcu_bh_qs(void);
Paul E. McKenneyc3377c2d2014-10-21 07:53:02 -0700335void rcu_check_callbacks(int user);
Thomas Gleixner27d50c72016-02-26 18:43:44 +0000336void rcu_report_dead(unsigned int cpu);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200337
Paul E. McKenney79cfea02015-12-07 13:09:52 -0800338#ifndef CONFIG_TINY_RCU
339void rcu_end_inkernel_boot(void);
340#else /* #ifndef CONFIG_TINY_RCU */
341static inline void rcu_end_inkernel_boot(void) { }
342#endif /* #ifndef CONFIG_TINY_RCU */
343
Rik van Riel61f38db2014-04-26 23:15:35 -0700344#ifdef CONFIG_RCU_STALL_COMMON
345void rcu_sysrq_start(void);
346void rcu_sysrq_end(void);
347#else /* #ifdef CONFIG_RCU_STALL_COMMON */
348static inline void rcu_sysrq_start(void)
349{
350}
351static inline void rcu_sysrq_end(void)
352{
353}
354#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
355
Paul E. McKenneyd1ec4c32015-05-13 10:41:58 -0700356#ifdef CONFIG_NO_HZ_FULL
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200357void rcu_user_enter(void);
358void rcu_user_exit(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200359#else
360static inline void rcu_user_enter(void) { }
361static inline void rcu_user_exit(void) { }
Paul E. McKenneyd1ec4c32015-05-13 10:41:58 -0700362#endif /* CONFIG_NO_HZ_FULL */
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200363
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -0700364#ifdef CONFIG_RCU_NOCB_CPU
365void rcu_init_nohz(void);
366#else /* #ifdef CONFIG_RCU_NOCB_CPU */
367static inline void rcu_init_nohz(void)
368{
369}
370#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
371
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800372/**
373 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
374 * @a: Code that RCU needs to pay attention to.
375 *
376 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
377 * in the inner idle loop, that is, between the rcu_idle_enter() and
378 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
379 * critical sections. However, things like powertop need tracepoints
380 * in the inner idle loop.
381 *
382 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
Paul E. McKenney810ce8b2016-04-20 09:22:15 -0700383 * will tell RCU that it needs to pay attention, invoke its argument
384 * (in this example, calling the do_something_with_RCU() function),
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800385 * and then tell RCU to go back to ignoring this CPU. It is permissible
Paul E. McKenney810ce8b2016-04-20 09:22:15 -0700386 * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
387 * on the order of a million or so, even on 32-bit systems). It is
388 * not legal to block within RCU_NONIDLE(), nor is it permissible to
389 * transfer control either into or out of RCU_NONIDLE()'s statement.
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800390 */
391#define RCU_NONIDLE(a) \
392 do { \
Paul E. McKenney7c9906c2015-10-31 00:59:01 -0700393 rcu_irq_enter_irqson(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800394 do { a; } while (0); \
Paul E. McKenney7c9906c2015-10-31 00:59:01 -0700395 rcu_irq_exit_irqson(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800396 } while (0)
397
Paul E. McKenney8315f422014-06-27 13:42:20 -0700398/*
399 * Note a voluntary context switch for RCU-tasks benefit. This is a
400 * macro rather than an inline function to avoid #include hell.
401 */
402#ifdef CONFIG_TASKS_RCU
Paul E. McKenney3f95aa82014-08-04 06:10:23 -0700403#define TASKS_RCU(x) x
404extern struct srcu_struct tasks_rcu_exit_srcu;
Paul E. McKenney8315f422014-06-27 13:42:20 -0700405#define rcu_note_voluntary_context_switch(t) \
406 do { \
Paul E. McKenney5cd37192014-12-13 20:32:04 -0800407 rcu_all_qs(); \
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800408 if (READ_ONCE((t)->rcu_tasks_holdout)) \
409 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
Paul E. McKenney8315f422014-06-27 13:42:20 -0700410 } while (0)
411#else /* #ifdef CONFIG_TASKS_RCU */
Paul E. McKenney3f95aa82014-08-04 06:10:23 -0700412#define TASKS_RCU(x) do { } while (0)
Paul E. McKenney5cd37192014-12-13 20:32:04 -0800413#define rcu_note_voluntary_context_switch(t) rcu_all_qs()
Paul E. McKenney8315f422014-06-27 13:42:20 -0700414#endif /* #else #ifdef CONFIG_TASKS_RCU */
415
Paul E. McKenneybde6c3a2014-07-01 11:26:57 -0700416/**
417 * cond_resched_rcu_qs - Report potential quiescent states to RCU
418 *
419 * This macro resembles cond_resched(), except that it is defined to
420 * report potential quiescent states to RCU-tasks even if the cond_resched()
421 * machinery were to be shut off, as some advocate for PREEMPT kernels.
422 */
423#define cond_resched_rcu_qs() \
424do { \
Paul E. McKenneyb6331ae2014-10-04 03:43:41 -0700425 if (!cond_resched()) \
426 rcu_note_voluntary_context_switch(current); \
Paul E. McKenneybde6c3a2014-07-01 11:26:57 -0700427} while (0)
428
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700429#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200430bool __rcu_is_watching(void);
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700431#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
432
Paul E. McKenney2c428182011-05-26 22:14:36 -0700433/*
434 * Infrastructure to implement the synchronize_() primitives in
435 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
436 */
437
Pranith Kumar28f65692014-09-22 14:00:48 -0400438#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100439#include <linux/rcutree.h>
Paul E. McKenney127781d2013-03-27 08:44:00 -0700440#elif defined(CONFIG_TINY_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700441#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100442#else
443#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700444#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100445
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400446/*
447 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
448 * initialization and destruction of rcu_head on the stack. rcu_head structures
449 * allocated dynamically in the heap or defined statically don't need any
450 * initialization.
451 */
452#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
Paul E. McKenney546a9d82014-06-19 14:57:10 -0700453void init_rcu_head(struct rcu_head *head);
454void destroy_rcu_head(struct rcu_head *head);
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200455void init_rcu_head_on_stack(struct rcu_head *head);
456void destroy_rcu_head_on_stack(struct rcu_head *head);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400457#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Paul E. McKenney546a9d82014-06-19 14:57:10 -0700458static inline void init_rcu_head(struct rcu_head *head)
459{
460}
461
462static inline void destroy_rcu_head(struct rcu_head *head)
463{
464}
465
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400466static inline void init_rcu_head_on_stack(struct rcu_head *head)
467{
468}
469
470static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
471{
472}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400473#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400474
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800475#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
476bool rcu_lockdep_current_cpu_online(void);
477#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
478static inline bool rcu_lockdep_current_cpu_online(void)
479{
Pranith Kumar521d24e2014-07-08 18:26:18 -0400480 return true;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800481}
482#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
483
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700484#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800485
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200486static inline void rcu_lock_acquire(struct lockdep_map *map)
487{
Oleg Nesterovfb9edbe2014-01-20 19:20:06 +0100488 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200489}
490
491static inline void rcu_lock_release(struct lockdep_map *map)
492{
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200493 lock_release(map, 1, _THIS_IP_);
494}
495
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700496extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800497extern struct lockdep_map rcu_bh_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800498extern struct lockdep_map rcu_sched_lock_map;
Paul E. McKenney24ef6592013-10-28 09:22:24 -0700499extern struct lockdep_map rcu_callback_map;
Iulia Mandaa235c092014-03-12 18:37:24 +0200500int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800501
Oleg Nesterov85b39d32014-07-08 15:17:59 -0700502int rcu_read_lock_held(void);
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200503int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800504
505/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700506 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800507 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700508 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
509 * RCU-sched read-side critical section. In absence of
510 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
Denys Vlasenkod5671f62015-05-26 17:48:34 +0200511 * critical section unless it can prove otherwise.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800512 */
Denys Vlasenkod5671f62015-05-26 17:48:34 +0200513int rcu_read_lock_sched_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800514
515#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
516
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200517# define rcu_lock_acquire(a) do { } while (0)
518# define rcu_lock_release(a) do { } while (0)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800519
520static inline int rcu_read_lock_held(void)
521{
522 return 1;
523}
524
525static inline int rcu_read_lock_bh_held(void)
526{
527 return 1;
528}
529
530static inline int rcu_read_lock_sched_held(void)
531{
Boqun Feng293e2422016-03-23 23:11:48 +0800532 return !preemptible();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800533}
Paul E. McKenney632ee202010-02-22 17:04:45 -0800534#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
535
536#ifdef CONFIG_PROVE_RCU
537
Tetsuo Handa4221a992010-06-26 01:08:19 +0900538/**
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700539 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
540 * @c: condition to check
541 * @s: informative message
542 */
543#define RCU_LOCKDEP_WARN(c, s) \
544 do { \
545 static bool __section(.data.unlikely) __warned; \
546 if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
547 __warned = true; \
548 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
549 } \
550 } while (0)
551
Paul E. McKenney50406b92012-01-12 13:49:19 -0800552#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
553static inline void rcu_preempt_sleep_check(void)
554{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700555 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
556 "Illegal context switch in RCU read-side critical section");
Paul E. McKenney50406b92012-01-12 13:49:19 -0800557}
558#else /* #ifdef CONFIG_PROVE_RCU */
559static inline void rcu_preempt_sleep_check(void)
560{
561}
562#endif /* #else #ifdef CONFIG_PROVE_RCU */
563
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700564#define rcu_sleep_check() \
565 do { \
Paul E. McKenney50406b92012-01-12 13:49:19 -0800566 rcu_preempt_sleep_check(); \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700567 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
568 "Illegal context switch in RCU-bh read-side critical section"); \
569 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
570 "Illegal context switch in RCU-sched read-side critical section"); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700571 } while (0)
572
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700573#else /* #ifdef CONFIG_PROVE_RCU */
574
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700575#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700576#define rcu_sleep_check() do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700577
578#endif /* #else #ifdef CONFIG_PROVE_RCU */
579
580/*
581 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
582 * and rcu_assign_pointer(). Some of these could be folded into their
583 * callers, but they are left separate in order to ease introduction of
584 * multiple flavors of pointers to match the multiple flavors of RCU
585 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
586 * the future.
587 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700588
589#ifdef __CHECKER__
590#define rcu_dereference_sparse(p, space) \
591 ((void)(((typeof(*p) space *)p) == p))
592#else /* #ifdef __CHECKER__ */
593#define rcu_dereference_sparse(p, space)
594#endif /* #else #ifdef __CHECKER__ */
595
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700596#define __rcu_access_pointer(p, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800597({ \
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800598 typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800599 rcu_dereference_sparse(p, space); \
600 ((typeof(*p) __force __kernel *)(_________p1)); \
601})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700602#define __rcu_dereference_check(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800603({ \
Pranith Kumarac598532014-11-13 14:24:14 -0500604 /* Dependency order vs. p above. */ \
605 typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700606 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800607 rcu_dereference_sparse(p, space); \
Pranith Kumarac598532014-11-13 14:24:14 -0500608 ((typeof(*p) __force __kernel *)(________p1)); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800609})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700610#define __rcu_dereference_protected(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800611({ \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700612 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800613 rcu_dereference_sparse(p, space); \
614 ((typeof(*p) __force __kernel *)(p)); \
615})
Paul E. McKenney995f1402016-07-01 13:44:53 -0700616#define rcu_dereference_raw(p) \
617({ \
618 /* Dependency order vs. p above. */ \
619 typeof(p) ________p1 = lockless_dereference(p); \
620 ((typeof(*p) __force __kernel *)(________p1)); \
621})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700622
Paul E. McKenney462225ae2013-11-11 09:59:34 -0800623/**
624 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
625 * @v: The value to statically initialize with.
626 */
627#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
628
629/**
630 * rcu_assign_pointer() - assign to RCU-protected pointer
631 * @p: pointer to assign to
632 * @v: value to assign (publish)
633 *
634 * Assigns the specified value to the specified RCU-protected
635 * pointer, ensuring that any concurrent RCU readers will see
636 * any prior initialization.
637 *
638 * Inserts memory barriers on architectures that require them
639 * (which is most of them), and also prevents the compiler from
640 * reordering the code that initializes the structure after the pointer
641 * assignment. More importantly, this call documents which pointers
642 * will be dereferenced by RCU read-side code.
643 *
644 * In some special cases, you may use RCU_INIT_POINTER() instead
645 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
646 * to the fact that it does not constrain either the CPU or the compiler.
647 * That said, using RCU_INIT_POINTER() when you should have used
648 * rcu_assign_pointer() is a very bad thing that results in
649 * impossible-to-diagnose memory corruption. So please be careful.
650 * See the RCU_INIT_POINTER() comment header for details.
651 *
652 * Note that rcu_assign_pointer() evaluates each of its arguments only
653 * once, appearances notwithstanding. One of the "extra" evaluations
654 * is in typeof() and the other visible only to sparse (__CHECKER__),
655 * neither of which actually execute the argument. As with most cpp
656 * macros, this execute-arguments-only-once property is important, so
657 * please be careful when making changes to rcu_assign_pointer() and the
658 * other macros that it invokes.
659 */
Paul E. McKenney3a37f722016-05-01 18:46:54 -0700660#define rcu_assign_pointer(p, v) \
661({ \
662 uintptr_t _r_a_p__v = (uintptr_t)(v); \
663 \
664 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
665 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
666 else \
667 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
668 _r_a_p__v; \
669})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700670
Paul E. McKenney632ee202010-02-22 17:04:45 -0800671/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700672 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
673 * @p: The pointer to read
674 *
675 * Return the value of the specified RCU-protected pointer, but omit the
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800676 * smp_read_barrier_depends() and keep the READ_ONCE(). This is useful
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700677 * when the value of this pointer is accessed, but the pointer is not
678 * dereferenced, for example, when testing an RCU-protected pointer against
679 * NULL. Although rcu_access_pointer() may also be used in cases where
680 * update-side locks prevent the value of the pointer from changing, you
681 * should instead use rcu_dereference_protected() for this use case.
Paul E. McKenney5e1ee6e2012-01-12 17:21:20 -0800682 *
683 * It is also permissible to use rcu_access_pointer() when read-side
684 * access to the pointer was removed at least one grace period ago, as
685 * is the case in the context of the RCU callback that is freeing up
686 * the data, or after a synchronize_rcu() returns. This can be useful
687 * when tearing down multi-linked structures after a grace period
688 * has elapsed.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700689 */
690#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
691
692/**
693 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700694 * @p: The pointer to read, prior to dereferencing
695 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800696 *
David Howellsc08c68d2010-04-09 15:39:11 -0700697 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700698 * dereference will take place are correct. Typically the conditions
699 * indicate the various locking conditions that should be held at that
700 * point. The check should return true if the conditions are satisfied.
701 * An implicit check for being in an RCU read-side critical section
702 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700703 *
704 * For example:
705 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700706 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700707 *
708 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700709 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700710 * the bar struct at foo->bar is held.
711 *
712 * Note that the list of conditions may also include indications of when a lock
713 * need not be held, for example during initialisation or destruction of the
714 * target struct:
715 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700716 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700717 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700718 *
719 * Inserts memory barriers on architectures that require them
720 * (currently only the Alpha), prevents the compiler from refetching
721 * (and from merging fetches), and, more importantly, documents exactly
722 * which pointers are protected by RCU and checks that the pointer is
723 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800724 */
725#define rcu_dereference_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800726 __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800727
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700728/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700729 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
730 * @p: The pointer to read, prior to dereferencing
731 * @c: The conditions under which the dereference will take place
732 *
733 * This is the RCU-bh counterpart to rcu_dereference_check().
734 */
735#define rcu_dereference_bh_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800736 __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700737
738/**
739 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
740 * @p: The pointer to read, prior to dereferencing
741 * @c: The conditions under which the dereference will take place
742 *
743 * This is the RCU-sched counterpart to rcu_dereference_check().
744 */
745#define rcu_dereference_sched_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800746 __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700747 __rcu)
748
Steven Rostedt12bcbe62013-05-28 14:38:42 -0400749/*
750 * The tracing infrastructure traces RCU (we want that), but unfortunately
751 * some of the RCU checks causes tracing to lock up the system.
752 *
Alexey Kardashevskiyf039f0a2015-11-02 13:21:47 +1100753 * The no-tracing version of rcu_dereference_raw() must not call
Steven Rostedt12bcbe62013-05-28 14:38:42 -0400754 * rcu_read_lock_held().
755 */
756#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
757
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700758/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700759 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
760 * @p: The pointer to read, prior to dereferencing
761 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700762 *
763 * Return the value of the specified RCU-protected pointer, but omit
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800764 * both the smp_read_barrier_depends() and the READ_ONCE(). This
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700765 * is useful in cases where update-side locks prevent the value of the
766 * pointer from changing. Please note that this primitive does -not-
767 * prevent the compiler from repeating this reference or combining it
768 * with other references, so it should not be used without protection
769 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700770 *
771 * This function is only for update-side use. Using this function
772 * when protected only by rcu_read_lock() will result in infrequent
773 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700774 */
775#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700776 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700777
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700778
779/**
780 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
781 * @p: The pointer to read, prior to dereferencing
782 *
783 * This is a simple wrapper around rcu_dereference_check().
784 */
785#define rcu_dereference(p) rcu_dereference_check(p, 0)
786
787/**
788 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
789 * @p: The pointer to read, prior to dereferencing
790 *
791 * Makes rcu_dereference_check() do the dirty work.
792 */
793#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
794
795/**
796 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
797 * @p: The pointer to read, prior to dereferencing
798 *
799 * Makes rcu_dereference_check() do the dirty work.
800 */
801#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
802
803/**
Paul E. McKenneyc3ac7cf2015-09-10 16:29:02 -0700804 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
805 * @p: The pointer to hand off
806 *
807 * This is simply an identity function, but it documents where a pointer
808 * is handed off from RCU to some other synchronization mechanism, for
809 * example, reference counting or locking. In C11, it would map to
810 * kill_dependency(). It could be used as follows:
811 *
812 * rcu_read_lock();
813 * p = rcu_dereference(gp);
814 * long_lived = is_long_lived(p);
815 * if (long_lived) {
816 * if (!atomic_inc_not_zero(p->refcnt))
817 * long_lived = false;
818 * else
819 * p = rcu_pointer_handoff(p);
820 * }
821 * rcu_read_unlock();
822 */
823#define rcu_pointer_handoff(p) (p)
824
825/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700826 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700827 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700828 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700829 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700830 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700831 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
832 * on one CPU while other CPUs are within RCU read-side critical
833 * sections, invocation of the corresponding RCU callback is deferred
834 * until after the all the other CPUs exit their critical sections.
835 *
836 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700837 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700838 * is via the following sequence of events: (1) CPU 0 enters an RCU
839 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
840 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
841 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
842 * callback is invoked. This is legal, because the RCU read-side critical
843 * section that was running concurrently with the call_rcu() (and which
844 * therefore might be referencing something that the corresponding RCU
845 * callback would free up) has completed before the corresponding
846 * RCU callback is invoked.
847 *
848 * RCU read-side critical sections may be nested. Any deferred actions
849 * will be deferred until the outermost RCU read-side critical section
850 * completes.
851 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700852 * You can avoid reading and understanding the next paragraph by
853 * following this rule: don't put anything in an rcu_read_lock() RCU
854 * read-side critical section that would block in a !PREEMPT kernel.
855 * But if you want the full story, read on!
856 *
Paul E. McKenneyab74fdf2014-05-04 15:41:21 -0700857 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
858 * it is illegal to block while in an RCU read-side critical section.
Pranith Kumar28f65692014-09-22 14:00:48 -0400859 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
Paul E. McKenneyab74fdf2014-05-04 15:41:21 -0700860 * kernel builds, RCU read-side critical sections may be preempted,
861 * but explicit blocking is illegal. Finally, in preemptible RCU
862 * implementations in real-time (with -rt patchset) kernel builds, RCU
863 * read-side critical sections may be preempted and they may also block, but
864 * only when acquiring spinlocks that are subject to priority inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700865 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700866static inline void rcu_read_lock(void)
867{
868 __rcu_read_lock();
869 __acquire(RCU);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200870 rcu_lock_acquire(&rcu_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700871 RCU_LOCKDEP_WARN(!rcu_is_watching(),
872 "rcu_read_lock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700873}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700874
Linus Torvalds1da177e2005-04-16 15:20:36 -0700875/*
876 * So where is rcu_write_lock()? It does not exist, as there is no
877 * way for writers to lock out RCU readers. This is a feature, not
878 * a bug -- this property is what provides RCU's performance benefits.
879 * Of course, writers must coordinate with each other. The normal
880 * spinlock primitives work well for this, but any other technique may be
881 * used as well. RCU does not care how the writers keep out of each
882 * others' way, as long as they do so.
883 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700884
885/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700886 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700887 *
Paul E. McKenneyf27bc482014-05-04 15:38:38 -0700888 * In most situations, rcu_read_unlock() is immune from deadlock.
889 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
890 * is responsible for deboosting, which it does via rt_mutex_unlock().
891 * Unfortunately, this function acquires the scheduler's runqueue and
892 * priority-inheritance spinlocks. This means that deadlock could result
893 * if the caller of rcu_read_unlock() already holds one of these locks or
Oleg Nesterovce36f2f2014-09-28 23:44:21 +0200894 * any lock that is ever acquired while holding them; or any lock which
895 * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
896 * does not disable irqs while taking ->wait_lock.
Paul E. McKenneyf27bc482014-05-04 15:38:38 -0700897 *
898 * That said, RCU readers are never priority boosted unless they were
899 * preempted. Therefore, one way to avoid deadlock is to make sure
900 * that preemption never happens within any RCU read-side critical
901 * section whose outermost rcu_read_unlock() is called with one of
902 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
903 * a number of ways, for example, by invoking preempt_disable() before
904 * critical section's outermost rcu_read_lock().
905 *
906 * Given that the set of locks acquired by rt_mutex_unlock() might change
907 * at any time, a somewhat more future-proofed approach is to make sure
908 * that that preemption never happens within any RCU read-side critical
909 * section whose outermost rcu_read_unlock() is called with irqs disabled.
910 * This approach relies on the fact that rt_mutex_unlock() currently only
911 * acquires irq-disabled locks.
912 *
913 * The second of these two approaches is best in most situations,
914 * however, the first approach can also be useful, at least to those
915 * developers willing to keep abreast of the set of locks acquired by
916 * rt_mutex_unlock().
917 *
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700918 * See rcu_read_lock() for more information.
919 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700920static inline void rcu_read_unlock(void)
921{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700922 RCU_LOCKDEP_WARN(!rcu_is_watching(),
923 "rcu_read_unlock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700924 __release(RCU);
925 __rcu_read_unlock();
Paul E. McKenneyd24209bb2015-01-21 15:26:03 -0800926 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700927}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700928
929/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700930 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700931 *
932 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700933 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
934 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
935 * softirq handler to be a quiescent state, a process in RCU read-side
936 * critical section must be protected by disabling softirqs. Read-side
937 * critical sections in interrupt context can use just rcu_read_lock(),
938 * though this should at least be commented to avoid confusing people
939 * reading the code.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800940 *
941 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
942 * must occur in the same context, for example, it is illegal to invoke
943 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
944 * was invoked from some other task.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700945 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700946static inline void rcu_read_lock_bh(void)
947{
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700948 local_bh_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700949 __acquire(RCU_BH);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200950 rcu_lock_acquire(&rcu_bh_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700951 RCU_LOCKDEP_WARN(!rcu_is_watching(),
952 "rcu_read_lock_bh() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700953}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700954
955/*
956 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
957 *
958 * See rcu_read_lock_bh() for more information.
959 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700960static inline void rcu_read_unlock_bh(void)
961{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700962 RCU_LOCKDEP_WARN(!rcu_is_watching(),
963 "rcu_read_unlock_bh() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200964 rcu_lock_release(&rcu_bh_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700965 __release(RCU_BH);
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700966 local_bh_enable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700967}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700968
969/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700970 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400971 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700972 * This is equivalent of rcu_read_lock(), but to be used when updates
973 * are being done using call_rcu_sched() or synchronize_rcu_sched().
974 * Read-side critical sections can also be introduced by anything that
975 * disables preemption, including local_irq_disable() and friends.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800976 *
977 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
978 * must occur in the same context, for example, it is illegal to invoke
979 * rcu_read_unlock_sched() from process context if the matching
980 * rcu_read_lock_sched() was invoked from an NMI handler.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400981 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700982static inline void rcu_read_lock_sched(void)
983{
984 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700985 __acquire(RCU_SCHED);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200986 rcu_lock_acquire(&rcu_sched_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700987 RCU_LOCKDEP_WARN(!rcu_is_watching(),
988 "rcu_read_lock_sched() used illegally while idle");
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700989}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700990
991/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700992static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700993{
994 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700995 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700996}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400997
998/*
999 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
1000 *
1001 * See rcu_read_lock_sched for more information.
1002 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001003static inline void rcu_read_unlock_sched(void)
1004{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -07001005 RCU_LOCKDEP_WARN(!rcu_is_watching(),
1006 "rcu_read_unlock_sched() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +02001007 rcu_lock_release(&rcu_sched_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -07001008 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001009 preempt_enable();
1010}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -07001011
1012/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -07001013static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001014{
Paul E. McKenneybc33f242009-08-22 13:56:47 -07001015 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001016 preempt_enable_notrace();
1017}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -04001018
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -04001019/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -07001020 * RCU_INIT_POINTER() - initialize an RCU protected pointer
1021 *
Paul E. McKenney6846c0c2011-07-31 22:33:02 -07001022 * Initialize an RCU-protected pointer in special cases where readers
1023 * do not need ordering constraints on the CPU or the compiler. These
1024 * special cases are:
1025 *
1026 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1027 * 2. The caller has taken whatever steps are required to prevent
1028 * RCU readers from concurrently accessing this pointer -or-
1029 * 3. The referenced data structure has already been exposed to
1030 * readers either at compile time or via rcu_assign_pointer() -and-
1031 * a. You have not made -any- reader-visible changes to
1032 * this structure since then -or-
1033 * b. It is OK for readers accessing this structure from its
1034 * new location to see the old state of the structure. (For
1035 * example, the changes were to statistical counters or to
1036 * other state where exact synchronization is not required.)
1037 *
1038 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1039 * result in impossible-to-diagnose memory corruption. As in the structures
1040 * will look OK in crash dumps, but any concurrent RCU readers might
1041 * see pre-initialized values of the referenced data structure. So
1042 * please be very careful how you use RCU_INIT_POINTER()!!!
1043 *
1044 * If you are creating an RCU-protected linked structure that is accessed
1045 * by a single external-to-structure RCU-protected pointer, then you may
1046 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1047 * pointers, but you must use rcu_assign_pointer() to initialize the
1048 * external-to-structure pointer -after- you have completely initialized
1049 * the reader-accessible portions of the linked structure.
Paul E. McKenney71a9b262014-03-31 13:13:02 -07001050 *
1051 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1052 * ordering guarantees for either the CPU or the compiler.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -07001053 */
1054#define RCU_INIT_POINTER(p, v) \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -07001055 do { \
Pranith Kumar1a6c9b22014-09-25 14:03:34 -04001056 rcu_dereference_sparse(p, __rcu); \
Peter Zijlstra155d1d12015-06-02 17:26:48 +02001057 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -07001058 } while (0)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001059
Paul E. McKenney172708d2012-05-16 15:23:45 -07001060/**
1061 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1062 *
1063 * GCC-style initialization for an RCU-protected pointer in a structure field.
1064 */
1065#define RCU_POINTER_INITIALIZER(p, v) \
Paul E. McKenney462225ae2013-11-11 09:59:34 -08001066 .p = RCU_INITIALIZER(v)
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001067
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001068/*
1069 * Does the specified offset indicate that the corresponding rcu_head
1070 * structure can be handled by kfree_rcu()?
1071 */
1072#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1073
1074/*
1075 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1076 */
1077#define __kfree_rcu(head, offset) \
1078 do { \
1079 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
Boqun Fengb6a4ae72015-07-29 13:29:38 +08001080 kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001081 } while (0)
1082
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001083/**
1084 * kfree_rcu() - kfree an object after a grace period.
1085 * @ptr: pointer to kfree
1086 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
1087 *
1088 * Many rcu callbacks functions just call kfree() on the base structure.
1089 * These functions are trivial, but their size adds up, and furthermore
1090 * when they are used in a kernel module, that module must invoke the
1091 * high-latency rcu_barrier() function at module-unload time.
1092 *
1093 * The kfree_rcu() function handles this issue. Rather than encoding a
1094 * function address in the embedded rcu_head structure, kfree_rcu() instead
1095 * encodes the offset of the rcu_head structure within the base structure.
1096 * Because the functions are not allowed in the low-order 4096 bytes of
1097 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1098 * If the offset is larger than 4095 bytes, a compile-time error will
1099 * be generated in __kfree_rcu(). If this error is triggered, you can
1100 * either fall back to use of call_rcu() or rearrange the structure to
1101 * position the rcu_head structure into the first 4096 bytes.
1102 *
1103 * Note that the allowable offset might decrease in the future, for example,
1104 * to allow something like kmem_cache_free_rcu().
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001105 *
1106 * The BUILD_BUG_ON check must not involve any function calls, hence the
1107 * checks are done in macros here.
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001108 */
1109#define kfree_rcu(ptr, rcu_head) \
1110 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1111
Paul E. McKenney3382adb2015-03-04 15:41:24 -08001112#ifdef CONFIG_TINY_RCU
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +00001113static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001114{
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +00001115 *nextevt = KTIME_MAX;
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001116 return 0;
1117}
Paul E. McKenney3382adb2015-03-04 15:41:24 -08001118#endif /* #ifdef CONFIG_TINY_RCU */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001119
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001120#if defined(CONFIG_RCU_NOCB_CPU_ALL)
1121static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1122#elif defined(CONFIG_RCU_NOCB_CPU)
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001123bool rcu_is_nocb_cpu(int cpu);
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001124#else
1125static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001126#endif
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001127
1128
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001129/* Only for use by adaptive-ticks code. */
1130#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001131bool rcu_sys_is_idle(void);
1132void rcu_sysidle_force_exit(void);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001133#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1134
1135static inline bool rcu_sys_is_idle(void)
1136{
1137 return false;
1138}
1139
1140static inline void rcu_sysidle_force_exit(void)
1141{
1142}
1143
1144#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1145
1146
Paul E. McKenney274529b2016-03-21 19:46:04 -07001147/*
1148 * Dump the ftrace buffer, but only one time per callsite per boot.
1149 */
1150#define rcu_ftrace_dump(oops_dump_mode) \
1151do { \
1152 static atomic_t ___rfd_beenhere = ATOMIC_INIT(0); \
1153 \
1154 if (!atomic_read(&___rfd_beenhere) && \
1155 !atomic_xchg(&___rfd_beenhere, 1)) \
1156 ftrace_dump(oops_dump_mode); \
1157} while (0)
1158
1159
Linus Torvalds1da177e2005-04-16 15:20:36 -07001160#endif /* __LINUX_RCUPDATE_H */