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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>
48
Paul E. McKenney88c18632013-12-16 13:24:32 -080049#include <asm/barrier.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070050
Paul E. McKenney79cfea02015-12-07 13:09:52 -080051#ifndef CONFIG_TINY_RCU
Paul Gortmaker7a754742014-02-11 16:10:12 -050052extern int rcu_expedited; /* for sysctl */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080053extern int rcu_normal; /* also for sysctl */
Paul E. McKenney79cfea02015-12-07 13:09:52 -080054#endif /* #ifndef CONFIG_TINY_RCU */
Dave Younge5ab6772010-03-10 15:24:05 -080055
Paul E. McKenney0d394822015-02-18 12:24:30 -080056#ifdef CONFIG_TINY_RCU
57/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080058static inline bool rcu_gp_is_normal(void) /* Internal RCU use. */
59{
60 return true;
61}
Paul E. McKenney0d394822015-02-18 12:24:30 -080062static inline bool rcu_gp_is_expedited(void) /* Internal RCU use. */
63{
64 return false;
65}
66
67static inline void rcu_expedite_gp(void)
68{
69}
70
71static inline void rcu_unexpedite_gp(void)
72{
73}
74#else /* #ifdef CONFIG_TINY_RCU */
Paul E. McKenney5a9be7c2015-11-24 15:44:06 -080075bool rcu_gp_is_normal(void); /* Internal RCU use. */
Paul E. McKenney0d394822015-02-18 12:24:30 -080076bool rcu_gp_is_expedited(void); /* Internal RCU use. */
77void rcu_expedite_gp(void);
78void rcu_unexpedite_gp(void);
79#endif /* #else #ifdef CONFIG_TINY_RCU */
80
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080081enum rcutorture_type {
82 RCU_FLAVOR,
83 RCU_BH_FLAVOR,
84 RCU_SCHED_FLAVOR,
Paul E. McKenney69c60452014-07-01 11:59:36 -070085 RCU_TASKS_FLAVOR,
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080086 SRCU_FLAVOR,
87 INVALID_RCU_FLAVOR
88};
89
Pranith Kumar28f65692014-09-22 14:00:48 -040090#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -080091void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
92 unsigned long *gpnum, unsigned long *completed);
Teodora Baluta584dc4c2013-11-11 17:11:23 +020093void rcutorture_record_test_transition(void);
94void rcutorture_record_progress(unsigned long vernum);
95void do_trace_rcu_torture_read(const char *rcutorturename,
96 struct rcu_head *rhp,
97 unsigned long secs,
98 unsigned long c_old,
99 unsigned long c);
Paul E. McKenney4a298652011-04-03 21:33:51 -0700100#else
Paul E. McKenneyad0dc7f2014-02-19 10:51:42 -0800101static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
102 int *flags,
103 unsigned long *gpnum,
104 unsigned long *completed)
105{
106 *flags = 0;
107 *gpnum = 0;
108 *completed = 0;
109}
Paul E. McKenney4a298652011-04-03 21:33:51 -0700110static inline void rcutorture_record_test_transition(void)
111{
112}
113static inline void rcutorture_record_progress(unsigned long vernum)
114{
115}
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700116#ifdef CONFIG_RCU_TRACE
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200117void do_trace_rcu_torture_read(const char *rcutorturename,
118 struct rcu_head *rhp,
119 unsigned long secs,
120 unsigned long c_old,
121 unsigned long c);
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700122#else
Paul E. McKenney52494532012-11-14 16:26:40 -0800123#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
124 do { } while (0)
Paul E. McKenney91afaf32011-10-02 07:44:32 -0700125#endif
Paul E. McKenney4a298652011-04-03 21:33:51 -0700126#endif
127
Tejun Heoe27fc962010-11-22 21:36:11 -0800128#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
129#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700130#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
131#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -0800132#define ulong2long(a) (*(long *)(&(a)))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700133
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700134/* Exported common interfaces */
Paul E. McKenney2c428182011-05-26 22:14:36 -0700135
136#ifdef CONFIG_PREEMPT_RCU
137
138/**
139 * call_rcu() - Queue an RCU callback for invocation after a grace period.
140 * @head: structure to be used for queueing the RCU updates.
141 * @func: actual callback function to be invoked after the grace period
142 *
143 * The callback function will be invoked some time after a full grace
144 * period elapses, in other words after all pre-existing RCU read-side
145 * critical sections have completed. However, the callback function
146 * might well execute concurrently with RCU read-side critical sections
147 * that started after call_rcu() was invoked. RCU read-side critical
148 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
149 * and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700150 *
151 * Note that all CPUs must agree that the grace period extended beyond
152 * all pre-existing RCU read-side critical section. On systems with more
153 * than one CPU, this means that when "func()" is invoked, each CPU is
154 * guaranteed to have executed a full memory barrier since the end of its
155 * last RCU read-side critical section whose beginning preceded the call
156 * to call_rcu(). It also means that each CPU executing an RCU read-side
157 * critical section that continues beyond the start of "func()" must have
158 * executed a memory barrier after the call_rcu() but before the beginning
159 * of that RCU read-side critical section. Note that these guarantees
160 * include CPUs that are offline, idle, or executing in user mode, as
161 * well as CPUs that are executing in the kernel.
162 *
163 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
164 * resulting RCU callback function "func()", then both CPU A and CPU B are
165 * guaranteed to execute a full memory barrier during the time interval
166 * between the call to call_rcu() and the invocation of "func()" -- even
167 * if CPU A and CPU B are the same CPU (but again only if the system has
168 * more than one CPU).
Paul E. McKenney2c428182011-05-26 22:14:36 -0700169 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200170void call_rcu(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800171 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700172
173#else /* #ifdef CONFIG_PREEMPT_RCU */
174
175/* In classic RCU, call_rcu() is just call_rcu_sched(). */
176#define call_rcu call_rcu_sched
177
178#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
179
180/**
181 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
182 * @head: structure to be used for queueing the RCU updates.
183 * @func: actual callback function to be invoked after the grace period
184 *
185 * The callback function will be invoked some time after a full grace
186 * period elapses, in other words after all currently executing RCU
187 * read-side critical sections have completed. call_rcu_bh() assumes
188 * that the read-side critical sections end on completion of a softirq
189 * handler. This means that read-side critical sections in process
190 * context must not be interrupted by softirqs. This interface is to be
191 * used when most of the read-side critical sections are in softirq context.
192 * RCU read-side critical sections are delimited by :
193 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
194 * OR
195 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
196 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700197 *
198 * See the description of call_rcu() for more detailed information on
199 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700200 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200201void call_rcu_bh(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800202 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700203
204/**
205 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
206 * @head: structure to be used for queueing the RCU updates.
207 * @func: actual callback function to be invoked after the grace period
208 *
209 * The callback function will be invoked some time after a full grace
210 * period elapses, in other words after all currently executing RCU
211 * read-side critical sections have completed. call_rcu_sched() assumes
212 * that the read-side critical sections end on enabling of preemption
213 * or on voluntary preemption.
214 * RCU read-side critical sections are delimited by :
215 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
216 * OR
217 * anything that disables preemption.
218 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700219 *
220 * See the description of call_rcu() for more detailed information on
221 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700222 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200223void call_rcu_sched(struct rcu_head *head,
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800224 rcu_callback_t func);
Paul E. McKenney2c428182011-05-26 22:14:36 -0700225
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200226void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700227
Paul E. McKenneyee376db2015-01-10 19:47:10 -0800228/*
229 * Structure allowing asynchronous waiting on RCU.
230 */
231struct rcu_synchronize {
232 struct rcu_head head;
233 struct completion completion;
234};
235void wakeme_after_rcu(struct rcu_head *head);
236
Paul E. McKenneyec90a192015-06-10 12:53:06 -0700237void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
238 struct rcu_synchronize *rs_array);
239
240#define _wait_rcu_gp(checktiny, ...) \
Oleg Nesterov66e8c572015-08-25 20:45:18 +0200241do { \
242 call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
243 struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)]; \
244 __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array), \
245 __crcu_array, __rs_array); \
Paul E. McKenneyec90a192015-06-10 12:53:06 -0700246} while (0)
247
248#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
249
250/**
251 * synchronize_rcu_mult - Wait concurrently for multiple grace periods
252 * @...: List of call_rcu() functions for the flavors to wait on.
253 *
254 * This macro waits concurrently for multiple flavors of RCU grace periods.
255 * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
256 * on concurrent RCU and RCU-bh grace periods. Waiting on a give SRCU
257 * domain requires you to write a wrapper function for that SRCU domain's
258 * call_srcu() function, supplying the corresponding srcu_struct.
259 *
260 * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
261 * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
262 * is automatically a grace period.
263 */
264#define synchronize_rcu_mult(...) \
265 _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
266
Paul E. McKenney8315f422014-06-27 13:42:20 -0700267/**
268 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
269 * @head: structure to be used for queueing the RCU updates.
270 * @func: actual callback function to be invoked after the grace period
271 *
272 * The callback 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. call_rcu_tasks() assumes
275 * that the read-side critical sections end at a voluntary context
276 * switch (not a preemption!), entry into idle, or transition to usermode
277 * execution. As such, there are no read-side primitives analogous to
278 * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
279 * to determine that all tasks have passed through a safe state, not so
280 * much for data-strcuture synchronization.
281 *
282 * See the description of call_rcu() for more detailed information on
283 * memory ordering guarantees.
284 */
Boqun Fengb6a4ae72015-07-29 13:29:38 +0800285void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
Paul E. McKenney53c6d4e2014-07-01 12:22:23 -0700286void synchronize_rcu_tasks(void);
287void rcu_barrier_tasks(void);
Paul E. McKenney8315f422014-06-27 13:42:20 -0700288
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700289#ifdef CONFIG_PREEMPT_RCU
290
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200291void __rcu_read_lock(void);
292void __rcu_read_unlock(void);
293void rcu_read_unlock_special(struct task_struct *t);
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700294void synchronize_rcu(void);
295
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700296/*
297 * Defined as a macro as it is a very low level header included from
298 * areas that don't even know about current. This gives the rcu_read_lock()
299 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
300 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
301 */
302#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
303
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700304#else /* #ifdef CONFIG_PREEMPT_RCU */
305
306static inline void __rcu_read_lock(void)
307{
Boqun Fengbb73c522015-07-30 16:55:38 -0700308 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
309 preempt_disable();
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700310}
311
312static inline void __rcu_read_unlock(void)
313{
Boqun Fengbb73c522015-07-30 16:55:38 -0700314 if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
315 preempt_enable();
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700316}
317
318static inline void synchronize_rcu(void)
319{
320 synchronize_sched();
321}
322
323static inline int rcu_preempt_depth(void)
324{
325 return 0;
326}
327
328#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
329
330/* Internal to kernel */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200331void rcu_init(void);
Paul E. McKenney284a8c92014-08-14 16:38:46 -0700332void rcu_sched_qs(void);
333void rcu_bh_qs(void);
Paul E. McKenneyc3377c2d2014-10-21 07:53:02 -0700334void rcu_check_callbacks(int user);
Thomas Gleixner27d50c72016-02-26 18:43:44 +0000335void rcu_report_dead(unsigned int cpu);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200336
Paul E. McKenney79cfea02015-12-07 13:09:52 -0800337#ifndef CONFIG_TINY_RCU
338void rcu_end_inkernel_boot(void);
339#else /* #ifndef CONFIG_TINY_RCU */
340static inline void rcu_end_inkernel_boot(void) { }
341#endif /* #ifndef CONFIG_TINY_RCU */
342
Rik van Riel61f38db2014-04-26 23:15:35 -0700343#ifdef CONFIG_RCU_STALL_COMMON
344void rcu_sysrq_start(void);
345void rcu_sysrq_end(void);
346#else /* #ifdef CONFIG_RCU_STALL_COMMON */
347static inline void rcu_sysrq_start(void)
348{
349}
350static inline void rcu_sysrq_end(void)
351{
352}
353#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
354
Paul E. McKenneyd1ec4c32015-05-13 10:41:58 -0700355#ifdef CONFIG_NO_HZ_FULL
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200356void rcu_user_enter(void);
357void rcu_user_exit(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200358#else
359static inline void rcu_user_enter(void) { }
360static inline void rcu_user_exit(void) { }
Paul E. McKenneyd1ec4c32015-05-13 10:41:58 -0700361#endif /* CONFIG_NO_HZ_FULL */
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200362
Paul E. McKenneyf4579fc2014-07-25 11:21:47 -0700363#ifdef CONFIG_RCU_NOCB_CPU
364void rcu_init_nohz(void);
365#else /* #ifdef CONFIG_RCU_NOCB_CPU */
366static inline void rcu_init_nohz(void)
367{
368}
369#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
370
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800371/**
372 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
373 * @a: Code that RCU needs to pay attention to.
374 *
375 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
376 * in the inner idle loop, that is, between the rcu_idle_enter() and
377 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
378 * critical sections. However, things like powertop need tracepoints
379 * in the inner idle loop.
380 *
381 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
Paul E. McKenney810ce8b2016-04-20 09:22:15 -0700382 * will tell RCU that it needs to pay attention, invoke its argument
383 * (in this example, calling the do_something_with_RCU() function),
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800384 * and then tell RCU to go back to ignoring this CPU. It is permissible
Paul E. McKenney810ce8b2016-04-20 09:22:15 -0700385 * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
386 * on the order of a million or so, even on 32-bit systems). It is
387 * not legal to block within RCU_NONIDLE(), nor is it permissible to
388 * transfer control either into or out of RCU_NONIDLE()'s statement.
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800389 */
390#define RCU_NONIDLE(a) \
391 do { \
Paul E. McKenney7c9906c2015-10-31 00:59:01 -0700392 rcu_irq_enter_irqson(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800393 do { a; } while (0); \
Paul E. McKenney7c9906c2015-10-31 00:59:01 -0700394 rcu_irq_exit_irqson(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800395 } while (0)
396
Paul E. McKenney8315f422014-06-27 13:42:20 -0700397/*
398 * Note a voluntary context switch for RCU-tasks benefit. This is a
399 * macro rather than an inline function to avoid #include hell.
400 */
401#ifdef CONFIG_TASKS_RCU
Paul E. McKenney3f95aa82014-08-04 06:10:23 -0700402#define TASKS_RCU(x) x
403extern struct srcu_struct tasks_rcu_exit_srcu;
Paul E. McKenney8315f422014-06-27 13:42:20 -0700404#define rcu_note_voluntary_context_switch(t) \
405 do { \
Paul E. McKenney5cd37192014-12-13 20:32:04 -0800406 rcu_all_qs(); \
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800407 if (READ_ONCE((t)->rcu_tasks_holdout)) \
408 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
Paul E. McKenney8315f422014-06-27 13:42:20 -0700409 } while (0)
410#else /* #ifdef CONFIG_TASKS_RCU */
Paul E. McKenney3f95aa82014-08-04 06:10:23 -0700411#define TASKS_RCU(x) do { } while (0)
Paul E. McKenney5cd37192014-12-13 20:32:04 -0800412#define rcu_note_voluntary_context_switch(t) rcu_all_qs()
Paul E. McKenney8315f422014-06-27 13:42:20 -0700413#endif /* #else #ifdef CONFIG_TASKS_RCU */
414
Paul E. McKenneybde6c3a2014-07-01 11:26:57 -0700415/**
416 * cond_resched_rcu_qs - Report potential quiescent states to RCU
417 *
418 * This macro resembles cond_resched(), except that it is defined to
419 * report potential quiescent states to RCU-tasks even if the cond_resched()
420 * machinery were to be shut off, as some advocate for PREEMPT kernels.
421 */
422#define cond_resched_rcu_qs() \
423do { \
Paul E. McKenneyb6331ae2014-10-04 03:43:41 -0700424 if (!cond_resched()) \
425 rcu_note_voluntary_context_switch(current); \
Paul E. McKenneybde6c3a2014-07-01 11:26:57 -0700426} while (0)
427
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700428#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200429bool __rcu_is_watching(void);
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700430#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
431
Paul E. McKenney2c428182011-05-26 22:14:36 -0700432/*
433 * Infrastructure to implement the synchronize_() primitives in
434 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
435 */
436
Pranith Kumar28f65692014-09-22 14:00:48 -0400437#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100438#include <linux/rcutree.h>
Paul E. McKenney127781d2013-03-27 08:44:00 -0700439#elif defined(CONFIG_TINY_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700440#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100441#else
442#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700443#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100444
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400445/*
446 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
447 * initialization and destruction of rcu_head on the stack. rcu_head structures
448 * allocated dynamically in the heap or defined statically don't need any
449 * initialization.
450 */
451#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
Paul E. McKenney546a9d82014-06-19 14:57:10 -0700452void init_rcu_head(struct rcu_head *head);
453void destroy_rcu_head(struct rcu_head *head);
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200454void init_rcu_head_on_stack(struct rcu_head *head);
455void destroy_rcu_head_on_stack(struct rcu_head *head);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400456#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Paul E. McKenney546a9d82014-06-19 14:57:10 -0700457static inline void init_rcu_head(struct rcu_head *head)
458{
459}
460
461static inline void destroy_rcu_head(struct rcu_head *head)
462{
463}
464
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400465static inline void init_rcu_head_on_stack(struct rcu_head *head)
466{
467}
468
469static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
470{
471}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400472#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400473
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800474#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
475bool rcu_lockdep_current_cpu_online(void);
476#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
477static inline bool rcu_lockdep_current_cpu_online(void)
478{
Pranith Kumar521d24e2014-07-08 18:26:18 -0400479 return true;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800480}
481#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
482
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700483#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800484
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200485static inline void rcu_lock_acquire(struct lockdep_map *map)
486{
Oleg Nesterovfb9edbe2014-01-20 19:20:06 +0100487 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200488}
489
490static inline void rcu_lock_release(struct lockdep_map *map)
491{
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200492 lock_release(map, 1, _THIS_IP_);
493}
494
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700495extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800496extern struct lockdep_map rcu_bh_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800497extern struct lockdep_map rcu_sched_lock_map;
Paul E. McKenney24ef6592013-10-28 09:22:24 -0700498extern struct lockdep_map rcu_callback_map;
Iulia Mandaa235c092014-03-12 18:37:24 +0200499int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800500
Oleg Nesterov85b39d32014-07-08 15:17:59 -0700501int rcu_read_lock_held(void);
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200502int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800503
504/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700505 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800506 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700507 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
508 * RCU-sched read-side critical section. In absence of
509 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
Denys Vlasenkod5671f62015-05-26 17:48:34 +0200510 * critical section unless it can prove otherwise.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800511 */
Denys Vlasenkod5671f62015-05-26 17:48:34 +0200512int rcu_read_lock_sched_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800513
514#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
515
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200516# define rcu_lock_acquire(a) do { } while (0)
517# define rcu_lock_release(a) do { } while (0)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800518
519static inline int rcu_read_lock_held(void)
520{
521 return 1;
522}
523
524static inline int rcu_read_lock_bh_held(void)
525{
526 return 1;
527}
528
529static inline int rcu_read_lock_sched_held(void)
530{
Boqun Feng293e2422016-03-23 23:11:48 +0800531 return !preemptible();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800532}
Paul E. McKenney632ee202010-02-22 17:04:45 -0800533#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
534
535#ifdef CONFIG_PROVE_RCU
536
Tetsuo Handa4221a992010-06-26 01:08:19 +0900537/**
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700538 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
539 * @c: condition to check
540 * @s: informative message
541 */
542#define RCU_LOCKDEP_WARN(c, s) \
543 do { \
544 static bool __section(.data.unlikely) __warned; \
545 if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
546 __warned = true; \
547 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
548 } \
549 } while (0)
550
Paul E. McKenney50406b92012-01-12 13:49:19 -0800551#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
552static inline void rcu_preempt_sleep_check(void)
553{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700554 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
555 "Illegal context switch in RCU read-side critical section");
Paul E. McKenney50406b92012-01-12 13:49:19 -0800556}
557#else /* #ifdef CONFIG_PROVE_RCU */
558static inline void rcu_preempt_sleep_check(void)
559{
560}
561#endif /* #else #ifdef CONFIG_PROVE_RCU */
562
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700563#define rcu_sleep_check() \
564 do { \
Paul E. McKenney50406b92012-01-12 13:49:19 -0800565 rcu_preempt_sleep_check(); \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700566 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
567 "Illegal context switch in RCU-bh read-side critical section"); \
568 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
569 "Illegal context switch in RCU-sched read-side critical section"); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700570 } while (0)
571
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700572#else /* #ifdef CONFIG_PROVE_RCU */
573
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700574#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700575#define rcu_sleep_check() do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700576
577#endif /* #else #ifdef CONFIG_PROVE_RCU */
578
579/*
580 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
581 * and rcu_assign_pointer(). Some of these could be folded into their
582 * callers, but they are left separate in order to ease introduction of
583 * multiple flavors of pointers to match the multiple flavors of RCU
584 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
585 * the future.
586 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700587
588#ifdef __CHECKER__
589#define rcu_dereference_sparse(p, space) \
590 ((void)(((typeof(*p) space *)p) == p))
591#else /* #ifdef __CHECKER__ */
592#define rcu_dereference_sparse(p, space)
593#endif /* #else #ifdef __CHECKER__ */
594
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700595#define __rcu_access_pointer(p, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800596({ \
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800597 typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800598 rcu_dereference_sparse(p, space); \
599 ((typeof(*p) __force __kernel *)(_________p1)); \
600})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700601#define __rcu_dereference_check(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800602({ \
Pranith Kumarac598532014-11-13 14:24:14 -0500603 /* Dependency order vs. p above. */ \
604 typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700605 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800606 rcu_dereference_sparse(p, space); \
Pranith Kumarac598532014-11-13 14:24:14 -0500607 ((typeof(*p) __force __kernel *)(________p1)); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800608})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700609#define __rcu_dereference_protected(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800610({ \
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700611 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
Joe Perches0adab9b2013-12-05 16:19:15 -0800612 rcu_dereference_sparse(p, space); \
613 ((typeof(*p) __force __kernel *)(p)); \
614})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700615
Paul E. McKenney462225ae2013-11-11 09:59:34 -0800616/**
617 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
618 * @v: The value to statically initialize with.
619 */
620#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
621
622/**
623 * rcu_assign_pointer() - assign to RCU-protected pointer
624 * @p: pointer to assign to
625 * @v: value to assign (publish)
626 *
627 * Assigns the specified value to the specified RCU-protected
628 * pointer, ensuring that any concurrent RCU readers will see
629 * any prior initialization.
630 *
631 * Inserts memory barriers on architectures that require them
632 * (which is most of them), and also prevents the compiler from
633 * reordering the code that initializes the structure after the pointer
634 * assignment. More importantly, this call documents which pointers
635 * will be dereferenced by RCU read-side code.
636 *
637 * In some special cases, you may use RCU_INIT_POINTER() instead
638 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
639 * to the fact that it does not constrain either the CPU or the compiler.
640 * That said, using RCU_INIT_POINTER() when you should have used
641 * rcu_assign_pointer() is a very bad thing that results in
642 * impossible-to-diagnose memory corruption. So please be careful.
643 * See the RCU_INIT_POINTER() comment header for details.
644 *
645 * Note that rcu_assign_pointer() evaluates each of its arguments only
646 * once, appearances notwithstanding. One of the "extra" evaluations
647 * is in typeof() and the other visible only to sparse (__CHECKER__),
648 * neither of which actually execute the argument. As with most cpp
649 * macros, this execute-arguments-only-once property is important, so
650 * please be careful when making changes to rcu_assign_pointer() and the
651 * other macros that it invokes.
652 */
Paul E. McKenney3a37f722016-05-01 18:46:54 -0700653#define rcu_assign_pointer(p, v) \
654({ \
655 uintptr_t _r_a_p__v = (uintptr_t)(v); \
656 \
657 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
658 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
659 else \
660 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
661 _r_a_p__v; \
662})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700663
Paul E. McKenney632ee202010-02-22 17:04:45 -0800664/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700665 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
666 * @p: The pointer to read
667 *
668 * Return the value of the specified RCU-protected pointer, but omit the
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800669 * smp_read_barrier_depends() and keep the READ_ONCE(). This is useful
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700670 * when the value of this pointer is accessed, but the pointer is not
671 * dereferenced, for example, when testing an RCU-protected pointer against
672 * NULL. Although rcu_access_pointer() may also be used in cases where
673 * update-side locks prevent the value of the pointer from changing, you
674 * should instead use rcu_dereference_protected() for this use case.
Paul E. McKenney5e1ee6e2012-01-12 17:21:20 -0800675 *
676 * It is also permissible to use rcu_access_pointer() when read-side
677 * access to the pointer was removed at least one grace period ago, as
678 * is the case in the context of the RCU callback that is freeing up
679 * the data, or after a synchronize_rcu() returns. This can be useful
680 * when tearing down multi-linked structures after a grace period
681 * has elapsed.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700682 */
683#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
684
685/**
686 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700687 * @p: The pointer to read, prior to dereferencing
688 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800689 *
David Howellsc08c68d2010-04-09 15:39:11 -0700690 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700691 * dereference will take place are correct. Typically the conditions
692 * indicate the various locking conditions that should be held at that
693 * point. The check should return true if the conditions are satisfied.
694 * An implicit check for being in an RCU read-side critical section
695 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700696 *
697 * For example:
698 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700699 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700700 *
701 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700702 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700703 * the bar struct at foo->bar is held.
704 *
705 * Note that the list of conditions may also include indications of when a lock
706 * need not be held, for example during initialisation or destruction of the
707 * target struct:
708 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700709 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700710 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700711 *
712 * Inserts memory barriers on architectures that require them
713 * (currently only the Alpha), prevents the compiler from refetching
714 * (and from merging fetches), and, more importantly, documents exactly
715 * which pointers are protected by RCU and checks that the pointer is
716 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800717 */
718#define rcu_dereference_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800719 __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800720
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700721/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700722 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
723 * @p: The pointer to read, prior to dereferencing
724 * @c: The conditions under which the dereference will take place
725 *
726 * This is the RCU-bh counterpart to rcu_dereference_check().
727 */
728#define rcu_dereference_bh_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800729 __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700730
731/**
732 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
733 * @p: The pointer to read, prior to dereferencing
734 * @c: The conditions under which the dereference will take place
735 *
736 * This is the RCU-sched counterpart to rcu_dereference_check().
737 */
738#define rcu_dereference_sched_check(p, c) \
Paul E. McKenneyb826565a2015-02-02 11:46:33 -0800739 __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700740 __rcu)
741
742#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
743
Steven Rostedt12bcbe62013-05-28 14:38:42 -0400744/*
745 * The tracing infrastructure traces RCU (we want that), but unfortunately
746 * some of the RCU checks causes tracing to lock up the system.
747 *
Alexey Kardashevskiyf039f0a2015-11-02 13:21:47 +1100748 * The no-tracing version of rcu_dereference_raw() must not call
Steven Rostedt12bcbe62013-05-28 14:38:42 -0400749 * rcu_read_lock_held().
750 */
751#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
752
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700753/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700754 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
755 * @p: The pointer to read, prior to dereferencing
756 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700757 *
758 * Return the value of the specified RCU-protected pointer, but omit
Paul E. McKenney7d0ae802015-03-03 14:57:58 -0800759 * both the smp_read_barrier_depends() and the READ_ONCE(). This
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700760 * is useful in cases where update-side locks prevent the value of the
761 * pointer from changing. Please note that this primitive does -not-
762 * prevent the compiler from repeating this reference or combining it
763 * with other references, so it should not be used without protection
764 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700765 *
766 * This function is only for update-side use. Using this function
767 * when protected only by rcu_read_lock() will result in infrequent
768 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700769 */
770#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700771 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700772
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700773
774/**
775 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
776 * @p: The pointer to read, prior to dereferencing
777 *
778 * This is a simple wrapper around rcu_dereference_check().
779 */
780#define rcu_dereference(p) rcu_dereference_check(p, 0)
781
782/**
783 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
784 * @p: The pointer to read, prior to dereferencing
785 *
786 * Makes rcu_dereference_check() do the dirty work.
787 */
788#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
789
790/**
791 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
792 * @p: The pointer to read, prior to dereferencing
793 *
794 * Makes rcu_dereference_check() do the dirty work.
795 */
796#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
797
798/**
Paul E. McKenneyc3ac7cf2015-09-10 16:29:02 -0700799 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
800 * @p: The pointer to hand off
801 *
802 * This is simply an identity function, but it documents where a pointer
803 * is handed off from RCU to some other synchronization mechanism, for
804 * example, reference counting or locking. In C11, it would map to
805 * kill_dependency(). It could be used as follows:
806 *
807 * rcu_read_lock();
808 * p = rcu_dereference(gp);
809 * long_lived = is_long_lived(p);
810 * if (long_lived) {
811 * if (!atomic_inc_not_zero(p->refcnt))
812 * long_lived = false;
813 * else
814 * p = rcu_pointer_handoff(p);
815 * }
816 * rcu_read_unlock();
817 */
818#define rcu_pointer_handoff(p) (p)
819
820/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700821 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700822 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700823 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700824 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700825 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700826 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
827 * on one CPU while other CPUs are within RCU read-side critical
828 * sections, invocation of the corresponding RCU callback is deferred
829 * until after the all the other CPUs exit their critical sections.
830 *
831 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700832 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700833 * is via the following sequence of events: (1) CPU 0 enters an RCU
834 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
835 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
836 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
837 * callback is invoked. This is legal, because the RCU read-side critical
838 * section that was running concurrently with the call_rcu() (and which
839 * therefore might be referencing something that the corresponding RCU
840 * callback would free up) has completed before the corresponding
841 * RCU callback is invoked.
842 *
843 * RCU read-side critical sections may be nested. Any deferred actions
844 * will be deferred until the outermost RCU read-side critical section
845 * completes.
846 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700847 * You can avoid reading and understanding the next paragraph by
848 * following this rule: don't put anything in an rcu_read_lock() RCU
849 * read-side critical section that would block in a !PREEMPT kernel.
850 * But if you want the full story, read on!
851 *
Paul E. McKenneyab74fdf2014-05-04 15:41:21 -0700852 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
853 * it is illegal to block while in an RCU read-side critical section.
Pranith Kumar28f65692014-09-22 14:00:48 -0400854 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
Paul E. McKenneyab74fdf2014-05-04 15:41:21 -0700855 * kernel builds, RCU read-side critical sections may be preempted,
856 * but explicit blocking is illegal. Finally, in preemptible RCU
857 * implementations in real-time (with -rt patchset) kernel builds, RCU
858 * read-side critical sections may be preempted and they may also block, but
859 * only when acquiring spinlocks that are subject to priority inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700860 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700861static inline void rcu_read_lock(void)
862{
863 __rcu_read_lock();
864 __acquire(RCU);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200865 rcu_lock_acquire(&rcu_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700866 RCU_LOCKDEP_WARN(!rcu_is_watching(),
867 "rcu_read_lock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700868}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700869
Linus Torvalds1da177e2005-04-16 15:20:36 -0700870/*
871 * So where is rcu_write_lock()? It does not exist, as there is no
872 * way for writers to lock out RCU readers. This is a feature, not
873 * a bug -- this property is what provides RCU's performance benefits.
874 * Of course, writers must coordinate with each other. The normal
875 * spinlock primitives work well for this, but any other technique may be
876 * used as well. RCU does not care how the writers keep out of each
877 * others' way, as long as they do so.
878 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700879
880/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700881 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700882 *
Paul E. McKenneyf27bc482014-05-04 15:38:38 -0700883 * In most situations, rcu_read_unlock() is immune from deadlock.
884 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
885 * is responsible for deboosting, which it does via rt_mutex_unlock().
886 * Unfortunately, this function acquires the scheduler's runqueue and
887 * priority-inheritance spinlocks. This means that deadlock could result
888 * if the caller of rcu_read_unlock() already holds one of these locks or
Oleg Nesterovce36f2f2014-09-28 23:44:21 +0200889 * any lock that is ever acquired while holding them; or any lock which
890 * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
891 * does not disable irqs while taking ->wait_lock.
Paul E. McKenneyf27bc482014-05-04 15:38:38 -0700892 *
893 * That said, RCU readers are never priority boosted unless they were
894 * preempted. Therefore, one way to avoid deadlock is to make sure
895 * that preemption never happens within any RCU read-side critical
896 * section whose outermost rcu_read_unlock() is called with one of
897 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
898 * a number of ways, for example, by invoking preempt_disable() before
899 * critical section's outermost rcu_read_lock().
900 *
901 * Given that the set of locks acquired by rt_mutex_unlock() might change
902 * at any time, a somewhat more future-proofed approach is to make sure
903 * that that preemption never happens within any RCU read-side critical
904 * section whose outermost rcu_read_unlock() is called with irqs disabled.
905 * This approach relies on the fact that rt_mutex_unlock() currently only
906 * acquires irq-disabled locks.
907 *
908 * The second of these two approaches is best in most situations,
909 * however, the first approach can also be useful, at least to those
910 * developers willing to keep abreast of the set of locks acquired by
911 * rt_mutex_unlock().
912 *
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700913 * See rcu_read_lock() for more information.
914 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700915static inline void rcu_read_unlock(void)
916{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700917 RCU_LOCKDEP_WARN(!rcu_is_watching(),
918 "rcu_read_unlock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700919 __release(RCU);
920 __rcu_read_unlock();
Paul E. McKenneyd24209bb2015-01-21 15:26:03 -0800921 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700922}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700923
924/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700925 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700926 *
927 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700928 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
929 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
930 * softirq handler to be a quiescent state, a process in RCU read-side
931 * critical section must be protected by disabling softirqs. Read-side
932 * critical sections in interrupt context can use just rcu_read_lock(),
933 * though this should at least be commented to avoid confusing people
934 * reading the code.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800935 *
936 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
937 * must occur in the same context, for example, it is illegal to invoke
938 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
939 * was invoked from some other task.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700940 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700941static inline void rcu_read_lock_bh(void)
942{
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700943 local_bh_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700944 __acquire(RCU_BH);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200945 rcu_lock_acquire(&rcu_bh_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700946 RCU_LOCKDEP_WARN(!rcu_is_watching(),
947 "rcu_read_lock_bh() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700948}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700949
950/*
951 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
952 *
953 * See rcu_read_lock_bh() for more information.
954 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700955static inline void rcu_read_unlock_bh(void)
956{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700957 RCU_LOCKDEP_WARN(!rcu_is_watching(),
958 "rcu_read_unlock_bh() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200959 rcu_lock_release(&rcu_bh_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700960 __release(RCU_BH);
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700961 local_bh_enable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700962}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700963
964/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700965 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400966 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700967 * This is equivalent of rcu_read_lock(), but to be used when updates
968 * are being done using call_rcu_sched() or synchronize_rcu_sched().
969 * Read-side critical sections can also be introduced by anything that
970 * disables preemption, including local_irq_disable() and friends.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800971 *
972 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
973 * must occur in the same context, for example, it is illegal to invoke
974 * rcu_read_unlock_sched() from process context if the matching
975 * rcu_read_lock_sched() was invoked from an NMI handler.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400976 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700977static inline void rcu_read_lock_sched(void)
978{
979 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700980 __acquire(RCU_SCHED);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200981 rcu_lock_acquire(&rcu_sched_lock_map);
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -0700982 RCU_LOCKDEP_WARN(!rcu_is_watching(),
983 "rcu_read_lock_sched() used illegally while idle");
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700984}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700985
986/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700987static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700988{
989 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700990 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700991}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400992
993/*
994 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
995 *
996 * See rcu_read_lock_sched for more information.
997 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700998static inline void rcu_read_unlock_sched(void)
999{
Paul E. McKenneyf78f5b92015-06-18 15:50:02 -07001000 RCU_LOCKDEP_WARN(!rcu_is_watching(),
1001 "rcu_read_unlock_sched() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +02001002 rcu_lock_release(&rcu_sched_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -07001003 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001004 preempt_enable();
1005}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -07001006
1007/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -07001008static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001009{
Paul E. McKenneybc33f242009-08-22 13:56:47 -07001010 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -07001011 preempt_enable_notrace();
1012}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -04001013
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -04001014/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -07001015 * RCU_INIT_POINTER() - initialize an RCU protected pointer
1016 *
Paul E. McKenney6846c0c2011-07-31 22:33:02 -07001017 * Initialize an RCU-protected pointer in special cases where readers
1018 * do not need ordering constraints on the CPU or the compiler. These
1019 * special cases are:
1020 *
1021 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
1022 * 2. The caller has taken whatever steps are required to prevent
1023 * RCU readers from concurrently accessing this pointer -or-
1024 * 3. The referenced data structure has already been exposed to
1025 * readers either at compile time or via rcu_assign_pointer() -and-
1026 * a. You have not made -any- reader-visible changes to
1027 * this structure since then -or-
1028 * b. It is OK for readers accessing this structure from its
1029 * new location to see the old state of the structure. (For
1030 * example, the changes were to statistical counters or to
1031 * other state where exact synchronization is not required.)
1032 *
1033 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1034 * result in impossible-to-diagnose memory corruption. As in the structures
1035 * will look OK in crash dumps, but any concurrent RCU readers might
1036 * see pre-initialized values of the referenced data structure. So
1037 * please be very careful how you use RCU_INIT_POINTER()!!!
1038 *
1039 * If you are creating an RCU-protected linked structure that is accessed
1040 * by a single external-to-structure RCU-protected pointer, then you may
1041 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1042 * pointers, but you must use rcu_assign_pointer() to initialize the
1043 * external-to-structure pointer -after- you have completely initialized
1044 * the reader-accessible portions of the linked structure.
Paul E. McKenney71a9b262014-03-31 13:13:02 -07001045 *
1046 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1047 * ordering guarantees for either the CPU or the compiler.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -07001048 */
1049#define RCU_INIT_POINTER(p, v) \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -07001050 do { \
Pranith Kumar1a6c9b22014-09-25 14:03:34 -04001051 rcu_dereference_sparse(p, __rcu); \
Peter Zijlstra155d1d12015-06-02 17:26:48 +02001052 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -07001053 } while (0)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001054
Paul E. McKenney172708d2012-05-16 15:23:45 -07001055/**
1056 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1057 *
1058 * GCC-style initialization for an RCU-protected pointer in a structure field.
1059 */
1060#define RCU_POINTER_INITIALIZER(p, v) \
Paul E. McKenney462225ae2013-11-11 09:59:34 -08001061 .p = RCU_INITIALIZER(v)
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001062
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001063/*
1064 * Does the specified offset indicate that the corresponding rcu_head
1065 * structure can be handled by kfree_rcu()?
1066 */
1067#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
1068
1069/*
1070 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
1071 */
1072#define __kfree_rcu(head, offset) \
1073 do { \
1074 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
Boqun Fengb6a4ae72015-07-29 13:29:38 +08001075 kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001076 } while (0)
1077
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001078/**
1079 * kfree_rcu() - kfree an object after a grace period.
1080 * @ptr: pointer to kfree
1081 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
1082 *
1083 * Many rcu callbacks functions just call kfree() on the base structure.
1084 * These functions are trivial, but their size adds up, and furthermore
1085 * when they are used in a kernel module, that module must invoke the
1086 * high-latency rcu_barrier() function at module-unload time.
1087 *
1088 * The kfree_rcu() function handles this issue. Rather than encoding a
1089 * function address in the embedded rcu_head structure, kfree_rcu() instead
1090 * encodes the offset of the rcu_head structure within the base structure.
1091 * Because the functions are not allowed in the low-order 4096 bytes of
1092 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
1093 * If the offset is larger than 4095 bytes, a compile-time error will
1094 * be generated in __kfree_rcu(). If this error is triggered, you can
1095 * either fall back to use of call_rcu() or rearrange the structure to
1096 * position the rcu_head structure into the first 4096 bytes.
1097 *
1098 * Note that the allowable offset might decrease in the future, for example,
1099 * to allow something like kmem_cache_free_rcu().
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001100 *
1101 * The BUILD_BUG_ON check must not involve any function calls, hence the
1102 * checks are done in macros here.
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001103 */
1104#define kfree_rcu(ptr, rcu_head) \
1105 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1106
Paul E. McKenney3382adb2015-03-04 15:41:24 -08001107#ifdef CONFIG_TINY_RCU
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +00001108static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001109{
Thomas Gleixnerc1ad3482015-04-14 21:08:58 +00001110 *nextevt = KTIME_MAX;
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001111 return 0;
1112}
Paul E. McKenney3382adb2015-03-04 15:41:24 -08001113#endif /* #ifdef CONFIG_TINY_RCU */
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001114
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001115#if defined(CONFIG_RCU_NOCB_CPU_ALL)
1116static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1117#elif defined(CONFIG_RCU_NOCB_CPU)
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001118bool rcu_is_nocb_cpu(int cpu);
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001119#else
1120static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001121#endif
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001122
1123
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001124/* Only for use by adaptive-ticks code. */
1125#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001126bool rcu_sys_is_idle(void);
1127void rcu_sysidle_force_exit(void);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001128#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1129
1130static inline bool rcu_sys_is_idle(void)
1131{
1132 return false;
1133}
1134
1135static inline void rcu_sysidle_force_exit(void)
1136{
1137}
1138
1139#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1140
1141
Paul E. McKenney274529b2016-03-21 19:46:04 -07001142/*
1143 * Dump the ftrace buffer, but only one time per callsite per boot.
1144 */
1145#define rcu_ftrace_dump(oops_dump_mode) \
1146do { \
1147 static atomic_t ___rfd_beenhere = ATOMIC_INIT(0); \
1148 \
1149 if (!atomic_read(&___rfd_beenhere) && \
1150 !atomic_xchg(&___rfd_beenhere, 1)) \
1151 ftrace_dump(oops_dump_mode); \
1152} while (0)
1153
1154
Linus Torvalds1da177e2005-04-16 15:20:36 -07001155#endif /* __LINUX_RCUPDATE_H */