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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>
Paul E. McKenney88c18632013-12-16 13:24:32 -080047#include <asm/barrier.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070048
Paul Gortmaker7a754742014-02-11 16:10:12 -050049extern int rcu_expedited; /* for sysctl */
Dave Younge5ab6772010-03-10 15:24:05 -080050#ifdef CONFIG_RCU_TORTURE_TEST
51extern int rcutorture_runnable; /* for sysctl */
52#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
53
Paul E. McKenney4a298652011-04-03 21:33:51 -070054#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Teodora Baluta584dc4c2013-11-11 17:11:23 +020055void rcutorture_record_test_transition(void);
56void rcutorture_record_progress(unsigned long vernum);
57void do_trace_rcu_torture_read(const char *rcutorturename,
58 struct rcu_head *rhp,
59 unsigned long secs,
60 unsigned long c_old,
61 unsigned long c);
Paul E. McKenney4a298652011-04-03 21:33:51 -070062#else
63static inline void rcutorture_record_test_transition(void)
64{
65}
66static inline void rcutorture_record_progress(unsigned long vernum)
67{
68}
Paul E. McKenney91afaf32011-10-02 07:44:32 -070069#ifdef CONFIG_RCU_TRACE
Teodora Baluta584dc4c2013-11-11 17:11:23 +020070void do_trace_rcu_torture_read(const char *rcutorturename,
71 struct rcu_head *rhp,
72 unsigned long secs,
73 unsigned long c_old,
74 unsigned long c);
Paul E. McKenney91afaf32011-10-02 07:44:32 -070075#else
Paul E. McKenney52494532012-11-14 16:26:40 -080076#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
77 do { } while (0)
Paul E. McKenney91afaf32011-10-02 07:44:32 -070078#endif
Paul E. McKenney4a298652011-04-03 21:33:51 -070079#endif
80
Tejun Heoe27fc962010-11-22 21:36:11 -080081#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
82#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070083#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
84#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
Paul E. McKenneyc0f4dfd2012-12-28 11:30:36 -080085#define ulong2long(a) (*(long *)(&(a)))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070086
Paul E. McKenney03b042b2009-06-25 09:08:16 -070087/* Exported common interfaces */
Paul E. McKenney2c428182011-05-26 22:14:36 -070088
89#ifdef CONFIG_PREEMPT_RCU
90
91/**
92 * call_rcu() - Queue an RCU callback for invocation after a grace period.
93 * @head: structure to be used for queueing the RCU updates.
94 * @func: actual callback function to be invoked after the grace period
95 *
96 * The callback function will be invoked some time after a full grace
97 * period elapses, in other words after all pre-existing RCU read-side
98 * critical sections have completed. However, the callback function
99 * might well execute concurrently with RCU read-side critical sections
100 * that started after call_rcu() was invoked. RCU read-side critical
101 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
102 * and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700103 *
104 * Note that all CPUs must agree that the grace period extended beyond
105 * all pre-existing RCU read-side critical section. On systems with more
106 * than one CPU, this means that when "func()" is invoked, each CPU is
107 * guaranteed to have executed a full memory barrier since the end of its
108 * last RCU read-side critical section whose beginning preceded the call
109 * to call_rcu(). It also means that each CPU executing an RCU read-side
110 * critical section that continues beyond the start of "func()" must have
111 * executed a memory barrier after the call_rcu() but before the beginning
112 * of that RCU read-side critical section. Note that these guarantees
113 * include CPUs that are offline, idle, or executing in user mode, as
114 * well as CPUs that are executing in the kernel.
115 *
116 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
117 * resulting RCU callback function "func()", then both CPU A and CPU B are
118 * guaranteed to execute a full memory barrier during the time interval
119 * between the call to call_rcu() and the invocation of "func()" -- even
120 * if CPU A and CPU B are the same CPU (but again only if the system has
121 * more than one CPU).
Paul E. McKenney2c428182011-05-26 22:14:36 -0700122 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200123void call_rcu(struct rcu_head *head,
124 void (*func)(struct rcu_head *head));
Paul E. McKenney2c428182011-05-26 22:14:36 -0700125
126#else /* #ifdef CONFIG_PREEMPT_RCU */
127
128/* In classic RCU, call_rcu() is just call_rcu_sched(). */
129#define call_rcu call_rcu_sched
130
131#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
132
133/**
134 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
135 * @head: structure to be used for queueing the RCU updates.
136 * @func: actual callback function to be invoked after the grace period
137 *
138 * The callback function will be invoked some time after a full grace
139 * period elapses, in other words after all currently executing RCU
140 * read-side critical sections have completed. call_rcu_bh() assumes
141 * that the read-side critical sections end on completion of a softirq
142 * handler. This means that read-side critical sections in process
143 * context must not be interrupted by softirqs. This interface is to be
144 * used when most of the read-side critical sections are in softirq context.
145 * RCU read-side critical sections are delimited by :
146 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
147 * OR
148 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
149 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700150 *
151 * See the description of call_rcu() for more detailed information on
152 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700153 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200154void call_rcu_bh(struct rcu_head *head,
155 void (*func)(struct rcu_head *head));
Paul E. McKenney2c428182011-05-26 22:14:36 -0700156
157/**
158 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
159 * @head: structure to be used for queueing the RCU updates.
160 * @func: actual callback function to be invoked after the grace period
161 *
162 * The callback function will be invoked some time after a full grace
163 * period elapses, in other words after all currently executing RCU
164 * read-side critical sections have completed. call_rcu_sched() assumes
165 * that the read-side critical sections end on enabling of preemption
166 * or on voluntary preemption.
167 * RCU read-side critical sections are delimited by :
168 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
169 * OR
170 * anything that disables preemption.
171 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700172 *
173 * See the description of call_rcu() for more detailed information on
174 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700175 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200176void call_rcu_sched(struct rcu_head *head,
177 void (*func)(struct rcu_head *rcu));
Paul E. McKenney2c428182011-05-26 22:14:36 -0700178
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200179void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700180
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700181#ifdef CONFIG_PREEMPT_RCU
182
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200183void __rcu_read_lock(void);
184void __rcu_read_unlock(void);
185void rcu_read_unlock_special(struct task_struct *t);
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700186void synchronize_rcu(void);
187
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700188/*
189 * Defined as a macro as it is a very low level header included from
190 * areas that don't even know about current. This gives the rcu_read_lock()
191 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
192 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
193 */
194#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
195
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700196#else /* #ifdef CONFIG_PREEMPT_RCU */
197
198static inline void __rcu_read_lock(void)
199{
200 preempt_disable();
201}
202
203static inline void __rcu_read_unlock(void)
204{
205 preempt_enable();
206}
207
208static inline void synchronize_rcu(void)
209{
210 synchronize_sched();
211}
212
213static inline int rcu_preempt_depth(void)
214{
215 return 0;
216}
217
218#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
219
220/* Internal to kernel */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200221void rcu_init(void);
222void rcu_sched_qs(int cpu);
223void rcu_bh_qs(int cpu);
224void rcu_check_callbacks(int cpu, int user);
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700225struct notifier_block;
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200226void rcu_idle_enter(void);
227void rcu_idle_exit(void);
228void rcu_irq_enter(void);
229void rcu_irq_exit(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200230
231#ifdef CONFIG_RCU_USER_QS
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200232void rcu_user_enter(void);
233void rcu_user_exit(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200234#else
235static inline void rcu_user_enter(void) { }
236static inline void rcu_user_exit(void) { }
Frederic Weisbecker4d9a5d42012-10-11 01:47:16 +0200237static inline void rcu_user_hooks_switch(struct task_struct *prev,
238 struct task_struct *next) { }
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200239#endif /* CONFIG_RCU_USER_QS */
240
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800241/**
242 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
243 * @a: Code that RCU needs to pay attention to.
244 *
245 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
246 * in the inner idle loop, that is, between the rcu_idle_enter() and
247 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
248 * critical sections. However, things like powertop need tracepoints
249 * in the inner idle loop.
250 *
251 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
252 * will tell RCU that it needs to pay attending, invoke its argument
253 * (in this example, a call to the do_something_with_RCU() function),
254 * and then tell RCU to go back to ignoring this CPU. It is permissible
255 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
256 * quite limited. If deeper nesting is required, it will be necessary
257 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800258 */
259#define RCU_NONIDLE(a) \
260 do { \
Paul E. McKenneyb4270ee2012-07-31 10:12:48 -0700261 rcu_irq_enter(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800262 do { a; } while (0); \
Paul E. McKenneyb4270ee2012-07-31 10:12:48 -0700263 rcu_irq_exit(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800264 } while (0)
265
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700266#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200267bool __rcu_is_watching(void);
Paul E. McKenneycc6783f2013-09-06 17:39:49 -0700268#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
269
Paul E. McKenney2c428182011-05-26 22:14:36 -0700270/*
271 * Infrastructure to implement the synchronize_() primitives in
272 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
273 */
274
275typedef void call_rcu_func_t(struct rcu_head *head,
276 void (*func)(struct rcu_head *head));
277void wait_rcu_gp(call_rcu_func_t crf);
278
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700279#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100280#include <linux/rcutree.h>
Paul E. McKenney127781d2013-03-27 08:44:00 -0700281#elif defined(CONFIG_TINY_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700282#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100283#else
284#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700285#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100286
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400287/*
288 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
289 * initialization and destruction of rcu_head on the stack. rcu_head structures
290 * allocated dynamically in the heap or defined statically don't need any
291 * initialization.
292 */
293#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200294void init_rcu_head_on_stack(struct rcu_head *head);
295void destroy_rcu_head_on_stack(struct rcu_head *head);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400296#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400297static inline void init_rcu_head_on_stack(struct rcu_head *head)
298{
299}
300
301static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
302{
303}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400304#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400305
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800306#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
307bool rcu_lockdep_current_cpu_online(void);
308#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
309static inline bool rcu_lockdep_current_cpu_online(void)
310{
311 return 1;
312}
313#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
314
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700315#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800316
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200317static inline void rcu_lock_acquire(struct lockdep_map *map)
318{
Oleg Nesterovfb9edbe2014-01-20 19:20:06 +0100319 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200320}
321
322static inline void rcu_lock_release(struct lockdep_map *map)
323{
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200324 lock_release(map, 1, _THIS_IP_);
325}
326
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700327extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800328extern struct lockdep_map rcu_bh_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800329extern struct lockdep_map rcu_sched_lock_map;
Paul E. McKenney24ef6592013-10-28 09:22:24 -0700330extern struct lockdep_map rcu_callback_map;
Paul E. McKenneybc293d62010-04-15 12:50:39 -0700331extern int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800332
Paul E. McKenney632ee202010-02-22 17:04:45 -0800333/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700334 * rcu_read_lock_held() - might we be in RCU read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800335 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700336 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
337 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
Paul E. McKenney632ee202010-02-22 17:04:45 -0800338 * this assumes we are in an RCU read-side critical section unless it can
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700339 * prove otherwise. This is useful for debug checks in functions that
340 * require that they be called within an RCU read-side critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800341 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700342 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700343 * and while lockdep is disabled.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800344 *
345 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
346 * occur in the same context, for example, it is illegal to invoke
347 * rcu_read_unlock() in process context if the matching rcu_read_lock()
348 * was invoked from within an irq handler.
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800349 *
350 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
351 * offline from an RCU perspective, so check for those as well.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800352 */
353static inline int rcu_read_lock_held(void)
354{
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800355 if (!debug_lockdep_rcu_enabled())
356 return 1;
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700357 if (!rcu_is_watching())
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700358 return 0;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800359 if (!rcu_lockdep_current_cpu_online())
360 return 0;
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800361 return lock_is_held(&rcu_lock_map);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800362}
363
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700364/*
365 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
366 * hell.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800367 */
Teodora Baluta584dc4c2013-11-11 17:11:23 +0200368int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800369
370/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700371 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800372 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700373 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
374 * RCU-sched read-side critical section. In absence of
375 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
376 * critical section unless it can prove otherwise. Note that disabling
377 * of preemption (including disabling irqs) counts as an RCU-sched
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700378 * read-side critical section. This is useful for debug checks in functions
379 * that required that they be called within an RCU-sched read-side
380 * critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800381 *
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700382 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
383 * and while lockdep is disabled.
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700384 *
385 * Note that if the CPU is in the idle loop from an RCU point of
386 * view (ie: that we are in the section between rcu_idle_enter() and
387 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
388 * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
389 * that are in such a section, considering these as in extended quiescent
390 * state, so such a CPU is effectively never in an RCU read-side critical
391 * section regardless of what RCU primitives it invokes. This state of
392 * affairs is required --- we need to keep an RCU-free window in idle
393 * where the CPU may possibly enter into low power mode. This way we can
394 * notice an extended quiescent state to other CPUs that started a grace
395 * period. Otherwise we would delay any grace period as long as we run in
396 * the idle task.
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800397 *
398 * Similarly, we avoid claiming an SRCU read lock held if the current
399 * CPU is offline.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800400 */
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200401#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800402static inline int rcu_read_lock_sched_held(void)
403{
404 int lockdep_opinion = 0;
405
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800406 if (!debug_lockdep_rcu_enabled())
407 return 1;
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700408 if (!rcu_is_watching())
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700409 return 0;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800410 if (!rcu_lockdep_current_cpu_online())
411 return 0;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800412 if (debug_locks)
413 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
Lai Jiangshan0cff8102010-03-18 12:25:33 -0700414 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800415}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200416#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800417static inline int rcu_read_lock_sched_held(void)
418{
419 return 1;
420}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200421#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800422
423#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
424
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200425# define rcu_lock_acquire(a) do { } while (0)
426# define rcu_lock_release(a) do { } while (0)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800427
428static inline int rcu_read_lock_held(void)
429{
430 return 1;
431}
432
433static inline int rcu_read_lock_bh_held(void)
434{
435 return 1;
436}
437
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200438#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800439static inline int rcu_read_lock_sched_held(void)
440{
Paul E. McKenneybbad9372010-04-02 16:17:17 -0700441 return preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800442}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200443#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800444static inline int rcu_read_lock_sched_held(void)
445{
446 return 1;
447}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200448#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800449
450#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
451
452#ifdef CONFIG_PROVE_RCU
453
Tetsuo Handa4221a992010-06-26 01:08:19 +0900454/**
455 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
456 * @c: condition to check
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700457 * @s: informative message
Tetsuo Handa4221a992010-06-26 01:08:19 +0900458 */
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700459#define rcu_lockdep_assert(c, s) \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800460 do { \
Jan Beulich7ccaba52012-03-23 15:01:52 -0700461 static bool __section(.data.unlikely) __warned; \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800462 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
463 __warned = true; \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700464 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800465 } \
466 } while (0)
467
Paul E. McKenney50406b92012-01-12 13:49:19 -0800468#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
469static inline void rcu_preempt_sleep_check(void)
470{
471 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
Paul E. McKenney5cf05ad2012-05-17 15:12:45 -0700472 "Illegal context switch in RCU read-side critical section");
Paul E. McKenney50406b92012-01-12 13:49:19 -0800473}
474#else /* #ifdef CONFIG_PROVE_RCU */
475static inline void rcu_preempt_sleep_check(void)
476{
477}
478#endif /* #else #ifdef CONFIG_PROVE_RCU */
479
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700480#define rcu_sleep_check() \
481 do { \
Paul E. McKenney50406b92012-01-12 13:49:19 -0800482 rcu_preempt_sleep_check(); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700483 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
Joe Perches41f4abd2013-12-05 15:10:23 -0800484 "Illegal context switch in RCU-bh read-side critical section"); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700485 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
Joe Perches41f4abd2013-12-05 15:10:23 -0800486 "Illegal context switch in RCU-sched read-side critical section"); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700487 } while (0)
488
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700489#else /* #ifdef CONFIG_PROVE_RCU */
490
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700491#define rcu_lockdep_assert(c, s) do { } while (0)
492#define rcu_sleep_check() do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700493
494#endif /* #else #ifdef CONFIG_PROVE_RCU */
495
496/*
497 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
498 * and rcu_assign_pointer(). Some of these could be folded into their
499 * callers, but they are left separate in order to ease introduction of
500 * multiple flavors of pointers to match the multiple flavors of RCU
501 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
502 * the future.
503 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700504
505#ifdef __CHECKER__
506#define rcu_dereference_sparse(p, space) \
507 ((void)(((typeof(*p) space *)p) == p))
508#else /* #ifdef __CHECKER__ */
509#define rcu_dereference_sparse(p, space)
510#endif /* #else #ifdef __CHECKER__ */
511
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700512#define __rcu_access_pointer(p, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800513({ \
514 typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
515 rcu_dereference_sparse(p, space); \
516 ((typeof(*p) __force __kernel *)(_________p1)); \
517})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700518#define __rcu_dereference_check(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800519({ \
520 typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
521 rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
522 rcu_dereference_sparse(p, space); \
523 smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
524 ((typeof(*p) __force __kernel *)(_________p1)); \
525})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700526#define __rcu_dereference_protected(p, c, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800527({ \
528 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
529 rcu_dereference_sparse(p, space); \
530 ((typeof(*p) __force __kernel *)(p)); \
531})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700532
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700533#define __rcu_access_index(p, space) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800534({ \
535 typeof(p) _________p1 = ACCESS_ONCE(p); \
536 rcu_dereference_sparse(p, space); \
537 (_________p1); \
538})
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700539#define __rcu_dereference_index_check(p, c) \
Joe Perches0adab9b2013-12-05 16:19:15 -0800540({ \
541 typeof(p) _________p1 = ACCESS_ONCE(p); \
542 rcu_lockdep_assert(c, \
543 "suspicious rcu_dereference_index_check() usage"); \
544 smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
545 (_________p1); \
546})
Paul E. McKenney462225ae2013-11-11 09:59:34 -0800547
548/**
549 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
550 * @v: The value to statically initialize with.
551 */
552#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
553
554/**
555 * rcu_assign_pointer() - assign to RCU-protected pointer
556 * @p: pointer to assign to
557 * @v: value to assign (publish)
558 *
559 * Assigns the specified value to the specified RCU-protected
560 * pointer, ensuring that any concurrent RCU readers will see
561 * any prior initialization.
562 *
563 * Inserts memory barriers on architectures that require them
564 * (which is most of them), and also prevents the compiler from
565 * reordering the code that initializes the structure after the pointer
566 * assignment. More importantly, this call documents which pointers
567 * will be dereferenced by RCU read-side code.
568 *
569 * In some special cases, you may use RCU_INIT_POINTER() instead
570 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
571 * to the fact that it does not constrain either the CPU or the compiler.
572 * That said, using RCU_INIT_POINTER() when you should have used
573 * rcu_assign_pointer() is a very bad thing that results in
574 * impossible-to-diagnose memory corruption. So please be careful.
575 * See the RCU_INIT_POINTER() comment header for details.
576 *
577 * Note that rcu_assign_pointer() evaluates each of its arguments only
578 * once, appearances notwithstanding. One of the "extra" evaluations
579 * is in typeof() and the other visible only to sparse (__CHECKER__),
580 * neither of which actually execute the argument. As with most cpp
581 * macros, this execute-arguments-only-once property is important, so
582 * please be careful when making changes to rcu_assign_pointer() and the
583 * other macros that it invokes.
584 */
Paul E. McKenney88c18632013-12-16 13:24:32 -0800585#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700586
Paul E. McKenney632ee202010-02-22 17:04:45 -0800587/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700588 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
589 * @p: The pointer to read
590 *
591 * Return the value of the specified RCU-protected pointer, but omit the
592 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
593 * when the value of this pointer is accessed, but the pointer is not
594 * dereferenced, for example, when testing an RCU-protected pointer against
595 * NULL. Although rcu_access_pointer() may also be used in cases where
596 * update-side locks prevent the value of the pointer from changing, you
597 * should instead use rcu_dereference_protected() for this use case.
Paul E. McKenney5e1ee6e2012-01-12 17:21:20 -0800598 *
599 * It is also permissible to use rcu_access_pointer() when read-side
600 * access to the pointer was removed at least one grace period ago, as
601 * is the case in the context of the RCU callback that is freeing up
602 * the data, or after a synchronize_rcu() returns. This can be useful
603 * when tearing down multi-linked structures after a grace period
604 * has elapsed.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700605 */
606#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
607
608/**
609 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700610 * @p: The pointer to read, prior to dereferencing
611 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800612 *
David Howellsc08c68d2010-04-09 15:39:11 -0700613 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700614 * dereference will take place are correct. Typically the conditions
615 * indicate the various locking conditions that should be held at that
616 * point. The check should return true if the conditions are satisfied.
617 * An implicit check for being in an RCU read-side critical section
618 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700619 *
620 * For example:
621 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700622 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700623 *
624 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700625 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700626 * the bar struct at foo->bar is held.
627 *
628 * Note that the list of conditions may also include indications of when a lock
629 * need not be held, for example during initialisation or destruction of the
630 * target struct:
631 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700632 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700633 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700634 *
635 * Inserts memory barriers on architectures that require them
636 * (currently only the Alpha), prevents the compiler from refetching
637 * (and from merging fetches), and, more importantly, documents exactly
638 * which pointers are protected by RCU and checks that the pointer is
639 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800640 */
641#define rcu_dereference_check(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700642 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800643
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700644/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700645 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
646 * @p: The pointer to read, prior to dereferencing
647 * @c: The conditions under which the dereference will take place
648 *
649 * This is the RCU-bh counterpart to rcu_dereference_check().
650 */
651#define rcu_dereference_bh_check(p, c) \
652 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
653
654/**
655 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
656 * @p: The pointer to read, prior to dereferencing
657 * @c: The conditions under which the dereference will take place
658 *
659 * This is the RCU-sched counterpart to rcu_dereference_check().
660 */
661#define rcu_dereference_sched_check(p, c) \
662 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
663 __rcu)
664
665#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
666
Steven Rostedt12bcbe62013-05-28 14:38:42 -0400667/*
668 * The tracing infrastructure traces RCU (we want that), but unfortunately
669 * some of the RCU checks causes tracing to lock up the system.
670 *
671 * The tracing version of rcu_dereference_raw() must not call
672 * rcu_read_lock_held().
673 */
674#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
675
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700676/**
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700677 * rcu_access_index() - fetch RCU index with no dereferencing
678 * @p: The index to read
679 *
680 * Return the value of the specified RCU-protected index, but omit the
681 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
682 * when the value of this index is accessed, but the index is not
683 * dereferenced, for example, when testing an RCU-protected index against
684 * -1. Although rcu_access_index() may also be used in cases where
685 * update-side locks prevent the value of the index from changing, you
686 * should instead use rcu_dereference_index_protected() for this use case.
687 */
688#define rcu_access_index(p) __rcu_access_index((p), __rcu)
689
690/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700691 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
692 * @p: The pointer to read, prior to dereferencing
693 * @c: The conditions under which the dereference will take place
694 *
695 * Similar to rcu_dereference_check(), but omits the sparse checking.
696 * This allows rcu_dereference_index_check() to be used on integers,
697 * which can then be used as array indices. Attempting to use
698 * rcu_dereference_check() on an integer will give compiler warnings
699 * because the sparse address-space mechanism relies on dereferencing
700 * the RCU-protected pointer. Dereferencing integers is not something
701 * that even gcc will put up with.
702 *
703 * Note that this function does not implicitly check for RCU read-side
704 * critical sections. If this function gains lots of uses, it might
705 * make sense to provide versions for each flavor of RCU, but it does
706 * not make sense as of early 2010.
707 */
708#define rcu_dereference_index_check(p, c) \
709 __rcu_dereference_index_check((p), (c))
710
711/**
712 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
713 * @p: The pointer to read, prior to dereferencing
714 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700715 *
716 * Return the value of the specified RCU-protected pointer, but omit
717 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
718 * is useful in cases where update-side locks prevent the value of the
719 * pointer from changing. Please note that this primitive does -not-
720 * prevent the compiler from repeating this reference or combining it
721 * with other references, so it should not be used without protection
722 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700723 *
724 * This function is only for update-side use. Using this function
725 * when protected only by rcu_read_lock() will result in infrequent
726 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700727 */
728#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700729 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700730
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700731
732/**
733 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
734 * @p: The pointer to read, prior to dereferencing
735 *
736 * This is a simple wrapper around rcu_dereference_check().
737 */
738#define rcu_dereference(p) rcu_dereference_check(p, 0)
739
740/**
741 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
742 * @p: The pointer to read, prior to dereferencing
743 *
744 * Makes rcu_dereference_check() do the dirty work.
745 */
746#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
747
748/**
749 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
750 * @p: The pointer to read, prior to dereferencing
751 *
752 * Makes rcu_dereference_check() do the dirty work.
753 */
754#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
755
756/**
757 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700758 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700759 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700760 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700761 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700762 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
763 * on one CPU while other CPUs are within RCU read-side critical
764 * sections, invocation of the corresponding RCU callback is deferred
765 * until after the all the other CPUs exit their critical sections.
766 *
767 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700768 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700769 * is via the following sequence of events: (1) CPU 0 enters an RCU
770 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
771 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
772 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
773 * callback is invoked. This is legal, because the RCU read-side critical
774 * section that was running concurrently with the call_rcu() (and which
775 * therefore might be referencing something that the corresponding RCU
776 * callback would free up) has completed before the corresponding
777 * RCU callback is invoked.
778 *
779 * RCU read-side critical sections may be nested. Any deferred actions
780 * will be deferred until the outermost RCU read-side critical section
781 * completes.
782 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700783 * You can avoid reading and understanding the next paragraph by
784 * following this rule: don't put anything in an rcu_read_lock() RCU
785 * read-side critical section that would block in a !PREEMPT kernel.
786 * But if you want the full story, read on!
787 *
788 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
789 * is illegal to block while in an RCU read-side critical section. In
790 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
791 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
792 * be preempted, but explicit blocking is illegal. Finally, in preemptible
Paul E. McKenney90f45e42013-01-10 05:24:49 -0800793 * RCU implementations in real-time (with -rt patchset) kernel builds,
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700794 * RCU read-side critical sections may be preempted and they may also
795 * block, but only when acquiring spinlocks that are subject to priority
796 * inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700797 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700798static inline void rcu_read_lock(void)
799{
800 __rcu_read_lock();
801 __acquire(RCU);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200802 rcu_lock_acquire(&rcu_lock_map);
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700803 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800804 "rcu_read_lock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700805}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700806
Linus Torvalds1da177e2005-04-16 15:20:36 -0700807/*
808 * So where is rcu_write_lock()? It does not exist, as there is no
809 * way for writers to lock out RCU readers. This is a feature, not
810 * a bug -- this property is what provides RCU's performance benefits.
811 * Of course, writers must coordinate with each other. The normal
812 * spinlock primitives work well for this, but any other technique may be
813 * used as well. RCU does not care how the writers keep out of each
814 * others' way, as long as they do so.
815 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700816
817/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700818 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700819 *
820 * See rcu_read_lock() for more information.
821 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700822static inline void rcu_read_unlock(void)
823{
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700824 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800825 "rcu_read_unlock() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200826 rcu_lock_release(&rcu_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700827 __release(RCU);
828 __rcu_read_unlock();
829}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700830
831/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700832 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700833 *
834 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700835 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
836 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
837 * softirq handler to be a quiescent state, a process in RCU read-side
838 * critical section must be protected by disabling softirqs. Read-side
839 * critical sections in interrupt context can use just rcu_read_lock(),
840 * though this should at least be commented to avoid confusing people
841 * reading the code.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800842 *
843 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
844 * must occur in the same context, for example, it is illegal to invoke
845 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
846 * was invoked from some other task.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700847 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700848static inline void rcu_read_lock_bh(void)
849{
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700850 local_bh_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700851 __acquire(RCU_BH);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200852 rcu_lock_acquire(&rcu_bh_lock_map);
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700853 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800854 "rcu_read_lock_bh() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700855}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700856
857/*
858 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
859 *
860 * See rcu_read_lock_bh() for more information.
861 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700862static inline void rcu_read_unlock_bh(void)
863{
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700864 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800865 "rcu_read_unlock_bh() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200866 rcu_lock_release(&rcu_bh_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700867 __release(RCU_BH);
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700868 local_bh_enable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700869}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700870
871/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700872 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400873 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700874 * This is equivalent of rcu_read_lock(), but to be used when updates
875 * are being done using call_rcu_sched() or synchronize_rcu_sched().
876 * Read-side critical sections can also be introduced by anything that
877 * disables preemption, including local_irq_disable() and friends.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800878 *
879 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
880 * must occur in the same context, for example, it is illegal to invoke
881 * rcu_read_unlock_sched() from process context if the matching
882 * rcu_read_lock_sched() was invoked from an NMI handler.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400883 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700884static inline void rcu_read_lock_sched(void)
885{
886 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700887 __acquire(RCU_SCHED);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200888 rcu_lock_acquire(&rcu_sched_lock_map);
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700889 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800890 "rcu_read_lock_sched() used illegally while idle");
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700891}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700892
893/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700894static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700895{
896 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700897 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700898}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400899
900/*
901 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
902 *
903 * See rcu_read_lock_sched for more information.
904 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700905static inline void rcu_read_unlock_sched(void)
906{
Paul E. McKenney5c173eb2013-09-13 17:20:11 -0700907 rcu_lockdep_assert(rcu_is_watching(),
Heiko Carstensbde23c62012-02-01 10:30:46 -0800908 "rcu_read_unlock_sched() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200909 rcu_lock_release(&rcu_sched_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700910 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700911 preempt_enable();
912}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700913
914/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700915static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700916{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700917 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700918 preempt_enable_notrace();
919}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400920
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400921/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700922 * RCU_INIT_POINTER() - initialize an RCU protected pointer
923 *
Paul E. McKenney6846c0c2011-07-31 22:33:02 -0700924 * Initialize an RCU-protected pointer in special cases where readers
925 * do not need ordering constraints on the CPU or the compiler. These
926 * special cases are:
927 *
928 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
929 * 2. The caller has taken whatever steps are required to prevent
930 * RCU readers from concurrently accessing this pointer -or-
931 * 3. The referenced data structure has already been exposed to
932 * readers either at compile time or via rcu_assign_pointer() -and-
933 * a. You have not made -any- reader-visible changes to
934 * this structure since then -or-
935 * b. It is OK for readers accessing this structure from its
936 * new location to see the old state of the structure. (For
937 * example, the changes were to statistical counters or to
938 * other state where exact synchronization is not required.)
939 *
940 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
941 * result in impossible-to-diagnose memory corruption. As in the structures
942 * will look OK in crash dumps, but any concurrent RCU readers might
943 * see pre-initialized values of the referenced data structure. So
944 * please be very careful how you use RCU_INIT_POINTER()!!!
945 *
946 * If you are creating an RCU-protected linked structure that is accessed
947 * by a single external-to-structure RCU-protected pointer, then you may
948 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
949 * pointers, but you must use rcu_assign_pointer() to initialize the
950 * external-to-structure pointer -after- you have completely initialized
951 * the reader-accessible portions of the linked structure.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700952 */
953#define RCU_INIT_POINTER(p, v) \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -0700954 do { \
Paul E. McKenney462225ae2013-11-11 09:59:34 -0800955 p = RCU_INITIALIZER(v); \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -0700956 } while (0)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700957
Paul E. McKenney172708d2012-05-16 15:23:45 -0700958/**
959 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
960 *
961 * GCC-style initialization for an RCU-protected pointer in a structure field.
962 */
963#define RCU_POINTER_INITIALIZER(p, v) \
Paul E. McKenney462225ae2013-11-11 09:59:34 -0800964 .p = RCU_INITIALIZER(v)
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800965
Jan Engelhardtd8169d42012-04-19 11:44:39 -0700966/*
967 * Does the specified offset indicate that the corresponding rcu_head
968 * structure can be handled by kfree_rcu()?
969 */
970#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
971
972/*
973 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
974 */
975#define __kfree_rcu(head, offset) \
976 do { \
977 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
Paul E. McKenney4fa3b6c2012-06-05 15:53:53 -0700978 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
Jan Engelhardtd8169d42012-04-19 11:44:39 -0700979 } while (0)
980
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800981/**
982 * kfree_rcu() - kfree an object after a grace period.
983 * @ptr: pointer to kfree
984 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
985 *
986 * Many rcu callbacks functions just call kfree() on the base structure.
987 * These functions are trivial, but their size adds up, and furthermore
988 * when they are used in a kernel module, that module must invoke the
989 * high-latency rcu_barrier() function at module-unload time.
990 *
991 * The kfree_rcu() function handles this issue. Rather than encoding a
992 * function address in the embedded rcu_head structure, kfree_rcu() instead
993 * encodes the offset of the rcu_head structure within the base structure.
994 * Because the functions are not allowed in the low-order 4096 bytes of
995 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
996 * If the offset is larger than 4095 bytes, a compile-time error will
997 * be generated in __kfree_rcu(). If this error is triggered, you can
998 * either fall back to use of call_rcu() or rearrange the structure to
999 * position the rcu_head structure into the first 4096 bytes.
1000 *
1001 * Note that the allowable offset might decrease in the future, for example,
1002 * to allow something like kmem_cache_free_rcu().
Jan Engelhardtd8169d42012-04-19 11:44:39 -07001003 *
1004 * The BUILD_BUG_ON check must not involve any function calls, hence the
1005 * checks are done in macros here.
Lai Jiangshan9ab15442011-03-18 11:15:47 +08001006 */
1007#define kfree_rcu(ptr, rcu_head) \
1008 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1009
Paul E. McKenneyffa83fb2013-11-17 19:27:16 -08001010#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
1011static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1012{
1013 *delta_jiffies = ULONG_MAX;
1014 return 0;
1015}
1016#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
1017
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001018#if defined(CONFIG_RCU_NOCB_CPU_ALL)
1019static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
1020#elif defined(CONFIG_RCU_NOCB_CPU)
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001021bool rcu_is_nocb_cpu(int cpu);
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001022#else
1023static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
Paul E. McKenney2f33b512013-11-17 18:25:48 -08001024#endif
Frederic Weisbeckerd1e43fa2013-03-26 23:47:24 +01001025
1026
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001027/* Only for use by adaptive-ticks code. */
1028#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
Teodora Baluta584dc4c2013-11-11 17:11:23 +02001029bool rcu_sys_is_idle(void);
1030void rcu_sysidle_force_exit(void);
Paul E. McKenney0edd1b12013-06-21 16:37:22 -07001031#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1032
1033static inline bool rcu_sys_is_idle(void)
1034{
1035 return false;
1036}
1037
1038static inline void rcu_sysidle_force_exit(void)
1039{
1040}
1041
1042#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
1043
1044
Linus Torvalds1da177e2005-04-16 15:20:36 -07001045#endif /* __LINUX_RCUPDATE_H */