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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
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
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>
Linus Torvalds1da177e2005-04-16 15:20:36 -070047
Dave Younge5ab6772010-03-10 15:24:05 -080048#ifdef CONFIG_RCU_TORTURE_TEST
49extern int rcutorture_runnable; /* for sysctl */
50#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
51
Paul E. McKenney4a298652011-04-03 21:33:51 -070052#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
53extern void rcutorture_record_test_transition(void);
54extern void rcutorture_record_progress(unsigned long vernum);
Paul E. McKenney91afaf32011-10-02 07:44:32 -070055extern void do_trace_rcu_torture_read(char *rcutorturename,
Paul E. McKenney52494532012-11-14 16:26:40 -080056 struct rcu_head *rhp,
57 unsigned long secs,
58 unsigned long c_old,
59 unsigned long c);
Paul E. McKenney4a298652011-04-03 21:33:51 -070060#else
61static inline void rcutorture_record_test_transition(void)
62{
63}
64static inline void rcutorture_record_progress(unsigned long vernum)
65{
66}
Paul E. McKenney91afaf32011-10-02 07:44:32 -070067#ifdef CONFIG_RCU_TRACE
68extern void do_trace_rcu_torture_read(char *rcutorturename,
Paul E. McKenney52494532012-11-14 16:26:40 -080069 struct rcu_head *rhp,
70 unsigned long secs,
71 unsigned long c_old,
72 unsigned long c);
Paul E. McKenney91afaf32011-10-02 07:44:32 -070073#else
Paul E. McKenney52494532012-11-14 16:26:40 -080074#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
75 do { } while (0)
Paul E. McKenney91afaf32011-10-02 07:44:32 -070076#endif
Paul E. McKenney4a298652011-04-03 21:33:51 -070077#endif
78
Tejun Heoe27fc962010-11-22 21:36:11 -080079#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
80#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -070081#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
82#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
83
Paul E. McKenney03b042b2009-06-25 09:08:16 -070084/* Exported common interfaces */
Paul E. McKenney2c428182011-05-26 22:14:36 -070085
86#ifdef CONFIG_PREEMPT_RCU
87
88/**
89 * call_rcu() - Queue an RCU callback for invocation after a grace period.
90 * @head: structure to be used for queueing the RCU updates.
91 * @func: actual callback function to be invoked after the grace period
92 *
93 * The callback function will be invoked some time after a full grace
94 * period elapses, in other words after all pre-existing RCU read-side
95 * critical sections have completed. However, the callback function
96 * might well execute concurrently with RCU read-side critical sections
97 * that started after call_rcu() was invoked. RCU read-side critical
98 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
99 * and may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700100 *
101 * Note that all CPUs must agree that the grace period extended beyond
102 * all pre-existing RCU read-side critical section. On systems with more
103 * than one CPU, this means that when "func()" is invoked, each CPU is
104 * guaranteed to have executed a full memory barrier since the end of its
105 * last RCU read-side critical section whose beginning preceded the call
106 * to call_rcu(). It also means that each CPU executing an RCU read-side
107 * critical section that continues beyond the start of "func()" must have
108 * executed a memory barrier after the call_rcu() but before the beginning
109 * of that RCU read-side critical section. Note that these guarantees
110 * include CPUs that are offline, idle, or executing in user mode, as
111 * well as CPUs that are executing in the kernel.
112 *
113 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
114 * resulting RCU callback function "func()", then both CPU A and CPU B are
115 * guaranteed to execute a full memory barrier during the time interval
116 * between the call to call_rcu() and the invocation of "func()" -- even
117 * if CPU A and CPU B are the same CPU (but again only if the system has
118 * more than one CPU).
Paul E. McKenney2c428182011-05-26 22:14:36 -0700119 */
120extern void call_rcu(struct rcu_head *head,
121 void (*func)(struct rcu_head *head));
122
123#else /* #ifdef CONFIG_PREEMPT_RCU */
124
125/* In classic RCU, call_rcu() is just call_rcu_sched(). */
126#define call_rcu call_rcu_sched
127
128#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
129
130/**
131 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
132 * @head: structure to be used for queueing the RCU updates.
133 * @func: actual callback function to be invoked after the grace period
134 *
135 * The callback function will be invoked some time after a full grace
136 * period elapses, in other words after all currently executing RCU
137 * read-side critical sections have completed. call_rcu_bh() assumes
138 * that the read-side critical sections end on completion of a softirq
139 * handler. This means that read-side critical sections in process
140 * context must not be interrupted by softirqs. This interface is to be
141 * used when most of the read-side critical sections are in softirq context.
142 * RCU read-side critical sections are delimited by :
143 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
144 * OR
145 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
146 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700147 *
148 * See the description of call_rcu() for more detailed information on
149 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700150 */
151extern void call_rcu_bh(struct rcu_head *head,
152 void (*func)(struct rcu_head *head));
153
154/**
155 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
156 * @head: structure to be used for queueing the RCU updates.
157 * @func: actual callback function to be invoked after the grace period
158 *
159 * The callback function will be invoked some time after a full grace
160 * period elapses, in other words after all currently executing RCU
161 * read-side critical sections have completed. call_rcu_sched() assumes
162 * that the read-side critical sections end on enabling of preemption
163 * or on voluntary preemption.
164 * RCU read-side critical sections are delimited by :
165 * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
166 * OR
167 * anything that disables preemption.
168 * These may be nested.
Paul E. McKenneyf0a0e6f2012-10-23 13:47:01 -0700169 *
170 * See the description of call_rcu() for more detailed information on
171 * memory ordering guarantees.
Paul E. McKenney2c428182011-05-26 22:14:36 -0700172 */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700173extern void call_rcu_sched(struct rcu_head *head,
174 void (*func)(struct rcu_head *rcu));
Paul E. McKenney2c428182011-05-26 22:14:36 -0700175
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700176extern void synchronize_sched(void);
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700177
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700178#ifdef CONFIG_PREEMPT_RCU
179
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700180extern void __rcu_read_lock(void);
181extern void __rcu_read_unlock(void);
Paul E. McKenney2a3fa842012-05-21 11:58:36 -0700182extern void rcu_read_unlock_special(struct task_struct *t);
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700183void synchronize_rcu(void);
184
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700185/*
186 * Defined as a macro as it is a very low level header included from
187 * areas that don't even know about current. This gives the rcu_read_lock()
188 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
189 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
190 */
191#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
192
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700193#else /* #ifdef CONFIG_PREEMPT_RCU */
194
195static inline void __rcu_read_lock(void)
196{
197 preempt_disable();
198}
199
200static inline void __rcu_read_unlock(void)
201{
202 preempt_enable();
203}
204
205static inline void synchronize_rcu(void)
206{
207 synchronize_sched();
208}
209
210static inline int rcu_preempt_depth(void)
211{
212 return 0;
213}
214
215#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
216
217/* Internal to kernel */
Paul E. McKenney7b0b7592010-08-17 14:18:46 -0700218extern void rcu_sched_qs(int cpu);
219extern void rcu_bh_qs(int cpu);
220extern void rcu_check_callbacks(int cpu, int user);
221struct notifier_block;
Paul E. McKenney9b2e4f12011-09-30 12:10:22 -0700222extern void rcu_idle_enter(void);
223extern void rcu_idle_exit(void);
224extern void rcu_irq_enter(void);
225extern void rcu_irq_exit(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200226
227#ifdef CONFIG_RCU_USER_QS
Frederic Weisbeckeradf50912012-06-28 11:20:21 -0700228extern void rcu_user_enter(void);
229extern void rcu_user_exit(void);
Frederic Weisbecker19dd15912012-06-04 16:42:35 -0700230extern void rcu_user_enter_after_irq(void);
231extern void rcu_user_exit_after_irq(void);
Frederic Weisbecker2b1d5022012-07-11 20:26:30 +0200232#else
233static inline void rcu_user_enter(void) { }
234static inline void rcu_user_exit(void) { }
235static inline void rcu_user_enter_after_irq(void) { }
236static inline void rcu_user_exit_after_irq(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. McKenney9dd8fb12012-04-13 12:54:22 -0700241extern void exit_rcu(void);
Paul E. McKenneya3dc3fb2010-08-13 16:16:25 -0700242
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800243/**
244 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
245 * @a: Code that RCU needs to pay attention to.
246 *
247 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
248 * in the inner idle loop, that is, between the rcu_idle_enter() and
249 * the rcu_idle_exit() -- RCU will happily ignore any such read-side
250 * critical sections. However, things like powertop need tracepoints
251 * in the inner idle loop.
252 *
253 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
254 * will tell RCU that it needs to pay attending, invoke its argument
255 * (in this example, a call to the do_something_with_RCU() function),
256 * and then tell RCU to go back to ignoring this CPU. It is permissible
257 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
258 * quite limited. If deeper nesting is required, it will be necessary
259 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800260 */
261#define RCU_NONIDLE(a) \
262 do { \
Paul E. McKenneyb4270ee2012-07-31 10:12:48 -0700263 rcu_irq_enter(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800264 do { a; } while (0); \
Paul E. McKenneyb4270ee2012-07-31 10:12:48 -0700265 rcu_irq_exit(); \
Paul E. McKenney8a2ecf42012-02-02 15:42:04 -0800266 } while (0)
267
Paul E. McKenney2c428182011-05-26 22:14:36 -0700268/*
269 * Infrastructure to implement the synchronize_() primitives in
270 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
271 */
272
273typedef void call_rcu_func_t(struct rcu_head *head,
274 void (*func)(struct rcu_head *head));
275void wait_rcu_gp(call_rcu_func_t crf);
276
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700277#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100278#include <linux/rcutree.h>
Paul E. McKenneya57eb942010-06-29 16:49:16 -0700279#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
Paul E. McKenney9b1d82f2009-10-25 19:03:50 -0700280#include <linux/rcutiny.h>
Paul E. McKenney64db4cf2008-12-18 21:55:32 +0100281#else
282#error "Unknown RCU implementation specified to kernel configuration"
Paul E. McKenney6b3ef482009-08-22 13:56:53 -0700283#endif
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100284
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400285/*
286 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
287 * initialization and destruction of rcu_head on the stack. rcu_head structures
288 * allocated dynamically in the heap or defined statically don't need any
289 * initialization.
290 */
291#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
292extern void init_rcu_head_on_stack(struct rcu_head *head);
293extern void destroy_rcu_head_on_stack(struct rcu_head *head);
294#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400295static inline void init_rcu_head_on_stack(struct rcu_head *head)
296{
297}
298
299static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
300{
301}
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400302#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
Mathieu Desnoyers43760302010-04-17 08:48:39 -0400303
Paul E. McKenney62fde6e2012-05-22 22:10:24 -0700304#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
305extern int rcu_is_cpu_idle(void);
306#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
307
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800308#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
309bool rcu_lockdep_current_cpu_online(void);
310#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
311static inline bool rcu_lockdep_current_cpu_online(void)
312{
313 return 1;
314}
315#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
316
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700317#ifdef CONFIG_DEBUG_LOCK_ALLOC
Paul E. McKenney632ee202010-02-22 17:04:45 -0800318
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200319static inline void rcu_lock_acquire(struct lockdep_map *map)
320{
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200321 lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
322}
323
324static inline void rcu_lock_release(struct lockdep_map *map)
325{
Frederic Weisbecker00f49e52011-10-07 18:22:02 +0200326 lock_release(map, 1, _THIS_IP_);
327}
328
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700329extern struct lockdep_map rcu_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800330extern struct lockdep_map rcu_bh_lock_map;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800331extern struct lockdep_map rcu_sched_lock_map;
Paul E. McKenneybc293d62010-04-15 12:50:39 -0700332extern int debug_lockdep_rcu_enabled(void);
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800333
Paul E. McKenney632ee202010-02-22 17:04:45 -0800334/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700335 * rcu_read_lock_held() - might we be in RCU read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800336 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700337 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
338 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
Paul E. McKenney632ee202010-02-22 17:04:45 -0800339 * this assumes we are in an RCU read-side critical section unless it can
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700340 * prove otherwise. This is useful for debug checks in functions that
341 * require that they be called within an RCU read-side critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800342 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700343 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700344 * and while lockdep is disabled.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800345 *
346 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
347 * occur in the same context, for example, it is illegal to invoke
348 * rcu_read_unlock() in process context if the matching rcu_read_lock()
349 * was invoked from within an irq handler.
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800350 *
351 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
352 * offline from an RCU perspective, so check for those as well.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800353 */
354static inline int rcu_read_lock_held(void)
355{
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800356 if (!debug_lockdep_rcu_enabled())
357 return 1;
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700358 if (rcu_is_cpu_idle())
359 return 0;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800360 if (!rcu_lockdep_current_cpu_online())
361 return 0;
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800362 return lock_is_held(&rcu_lock_map);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800363}
364
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700365/*
366 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
367 * hell.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800368 */
Paul E. McKenneye3818b82010-03-15 17:03:43 -0700369extern int rcu_read_lock_bh_held(void);
Paul E. McKenney632ee202010-02-22 17:04:45 -0800370
371/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700372 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
Paul E. McKenney632ee202010-02-22 17:04:45 -0800373 *
Paul E. McKenneyd20200b2010-03-30 10:52:21 -0700374 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
375 * RCU-sched read-side critical section. In absence of
376 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
377 * critical section unless it can prove otherwise. Note that disabling
378 * of preemption (including disabling irqs) counts as an RCU-sched
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700379 * read-side critical section. This is useful for debug checks in functions
380 * that required that they be called within an RCU-sched read-side
381 * critical section.
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800382 *
Paul E. McKenney32c141a2010-03-30 10:59:28 -0700383 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
384 * and while lockdep is disabled.
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700385 *
386 * Note that if the CPU is in the idle loop from an RCU point of
387 * view (ie: that we are in the section between rcu_idle_enter() and
388 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
389 * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
390 * that are in such a section, considering these as in extended quiescent
391 * state, so such a CPU is effectively never in an RCU read-side critical
392 * section regardless of what RCU primitives it invokes. This state of
393 * affairs is required --- we need to keep an RCU-free window in idle
394 * where the CPU may possibly enter into low power mode. This way we can
395 * notice an extended quiescent state to other CPUs that started a grace
396 * period. Otherwise we would delay any grace period as long as we run in
397 * the idle task.
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800398 *
399 * Similarly, we avoid claiming an SRCU read lock held if the current
400 * CPU is offline.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800401 */
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200402#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800403static inline int rcu_read_lock_sched_held(void)
404{
405 int lockdep_opinion = 0;
406
Paul E. McKenney54dbf962010-03-03 07:46:57 -0800407 if (!debug_lockdep_rcu_enabled())
408 return 1;
Frederic Weisbeckere6b80a32011-10-07 16:25:18 -0700409 if (rcu_is_cpu_idle())
410 return 0;
Paul E. McKenneyc0d6d012012-01-23 12:41:26 -0800411 if (!rcu_lockdep_current_cpu_online())
412 return 0;
Paul E. McKenney632ee202010-02-22 17:04:45 -0800413 if (debug_locks)
414 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
Lai Jiangshan0cff8102010-03-18 12:25:33 -0700415 return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800416}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200417#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800418static inline int rcu_read_lock_sched_held(void)
419{
420 return 1;
421}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200422#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800423
424#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
425
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200426# define rcu_lock_acquire(a) do { } while (0)
427# define rcu_lock_release(a) do { } while (0)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800428
429static inline int rcu_read_lock_held(void)
430{
431 return 1;
432}
433
434static inline int rcu_read_lock_bh_held(void)
435{
436 return 1;
437}
438
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200439#ifdef CONFIG_PREEMPT_COUNT
Paul E. McKenney632ee202010-02-22 17:04:45 -0800440static inline int rcu_read_lock_sched_held(void)
441{
Paul E. McKenneybbad9372010-04-02 16:17:17 -0700442 return preempt_count() != 0 || irqs_disabled();
Paul E. McKenney632ee202010-02-22 17:04:45 -0800443}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200444#else /* #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenneye6033e32010-03-03 17:50:16 -0800445static inline int rcu_read_lock_sched_held(void)
446{
447 return 1;
448}
Frederic Weisbeckerbdd4e852011-06-08 01:13:27 +0200449#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
Paul E. McKenney632ee202010-02-22 17:04:45 -0800450
451#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
452
453#ifdef CONFIG_PROVE_RCU
454
Paul E. McKenneyee84b822010-05-06 09:28:41 -0700455extern int rcu_my_thread_group_empty(void);
456
Tetsuo Handa4221a992010-06-26 01:08:19 +0900457/**
458 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
459 * @c: condition to check
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700460 * @s: informative message
Tetsuo Handa4221a992010-06-26 01:08:19 +0900461 */
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700462#define rcu_lockdep_assert(c, s) \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800463 do { \
Jan Beulich7ccaba52012-03-23 15:01:52 -0700464 static bool __section(.data.unlikely) __warned; \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800465 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
466 __warned = true; \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700467 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
Lai Jiangshan2b3fc352010-04-20 16:23:07 +0800468 } \
469 } while (0)
470
Paul E. McKenney50406b92012-01-12 13:49:19 -0800471#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
472static inline void rcu_preempt_sleep_check(void)
473{
474 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
Paul E. McKenney5cf05ad2012-05-17 15:12:45 -0700475 "Illegal context switch in RCU read-side critical section");
Paul E. McKenney50406b92012-01-12 13:49:19 -0800476}
477#else /* #ifdef CONFIG_PROVE_RCU */
478static inline void rcu_preempt_sleep_check(void)
479{
480}
481#endif /* #else #ifdef CONFIG_PROVE_RCU */
482
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700483#define rcu_sleep_check() \
484 do { \
Paul E. McKenney50406b92012-01-12 13:49:19 -0800485 rcu_preempt_sleep_check(); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700486 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
487 "Illegal context switch in RCU-bh" \
488 " read-side critical section"); \
489 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
490 "Illegal context switch in RCU-sched"\
491 " read-side critical section"); \
492 } while (0)
493
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700494#else /* #ifdef CONFIG_PROVE_RCU */
495
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700496#define rcu_lockdep_assert(c, s) do { } while (0)
497#define rcu_sleep_check() do { } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700498
499#endif /* #else #ifdef CONFIG_PROVE_RCU */
500
501/*
502 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
503 * and rcu_assign_pointer(). Some of these could be folded into their
504 * callers, but they are left separate in order to ease introduction of
505 * multiple flavors of pointers to match the multiple flavors of RCU
506 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
507 * the future.
508 */
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700509
510#ifdef __CHECKER__
511#define rcu_dereference_sparse(p, space) \
512 ((void)(((typeof(*p) space *)p) == p))
513#else /* #ifdef __CHECKER__ */
514#define rcu_dereference_sparse(p, space)
515#endif /* #else #ifdef __CHECKER__ */
516
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700517#define __rcu_access_pointer(p, space) \
518 ({ \
519 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700520 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700521 ((typeof(*p) __force __kernel *)(_________p1)); \
522 })
523#define __rcu_dereference_check(p, c, space) \
524 ({ \
525 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700526 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
527 " usage"); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700528 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700529 smp_read_barrier_depends(); \
530 ((typeof(*p) __force __kernel *)(_________p1)); \
531 })
532#define __rcu_dereference_protected(p, c, space) \
533 ({ \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700534 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
535 " usage"); \
Paul E. McKenney53ecfba2010-09-13 17:24:21 -0700536 rcu_dereference_sparse(p, space); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700537 ((typeof(*p) __force __kernel *)(p)); \
538 })
539
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700540#define __rcu_access_index(p, space) \
541 ({ \
542 typeof(p) _________p1 = ACCESS_ONCE(p); \
543 rcu_dereference_sparse(p, space); \
544 (_________p1); \
545 })
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700546#define __rcu_dereference_index_check(p, c) \
547 ({ \
548 typeof(p) _________p1 = ACCESS_ONCE(p); \
Paul E. McKenneyb3fbab02011-05-24 08:31:09 -0700549 rcu_lockdep_assert(c, \
550 "suspicious rcu_dereference_index_check()" \
551 " usage"); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700552 smp_read_barrier_depends(); \
553 (_________p1); \
554 })
555#define __rcu_assign_pointer(p, v, space) \
Paul E. McKenneye9023c42012-05-16 15:51:08 -0700556 do { \
Eric Dumazetd322f452011-07-31 22:09:25 -0700557 smp_wmb(); \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700558 (p) = (typeof(*v) __force space *)(v); \
Paul E. McKenneye9023c42012-05-16 15:51:08 -0700559 } while (0)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700560
561
Paul E. McKenney632ee202010-02-22 17:04:45 -0800562/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700563 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
564 * @p: The pointer to read
565 *
566 * Return the value of the specified RCU-protected pointer, but omit the
567 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
568 * when the value of this pointer is accessed, but the pointer is not
569 * dereferenced, for example, when testing an RCU-protected pointer against
570 * NULL. Although rcu_access_pointer() may also be used in cases where
571 * update-side locks prevent the value of the pointer from changing, you
572 * should instead use rcu_dereference_protected() for this use case.
Paul E. McKenney5e1ee6e2012-01-12 17:21:20 -0800573 *
574 * It is also permissible to use rcu_access_pointer() when read-side
575 * access to the pointer was removed at least one grace period ago, as
576 * is the case in the context of the RCU callback that is freeing up
577 * the data, or after a synchronize_rcu() returns. This can be useful
578 * when tearing down multi-linked structures after a grace period
579 * has elapsed.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700580 */
581#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
582
583/**
584 * rcu_dereference_check() - rcu_dereference with debug checking
David Howellsc08c68d2010-04-09 15:39:11 -0700585 * @p: The pointer to read, prior to dereferencing
586 * @c: The conditions under which the dereference will take place
Paul E. McKenney632ee202010-02-22 17:04:45 -0800587 *
David Howellsc08c68d2010-04-09 15:39:11 -0700588 * Do an rcu_dereference(), but check that the conditions under which the
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700589 * dereference will take place are correct. Typically the conditions
590 * indicate the various locking conditions that should be held at that
591 * point. The check should return true if the conditions are satisfied.
592 * An implicit check for being in an RCU read-side critical section
593 * (rcu_read_lock()) is included.
David Howellsc08c68d2010-04-09 15:39:11 -0700594 *
595 * For example:
596 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700597 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
David Howellsc08c68d2010-04-09 15:39:11 -0700598 *
599 * could be used to indicate to lockdep that foo->bar may only be dereferenced
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700600 * if either rcu_read_lock() is held, or that the lock required to replace
David Howellsc08c68d2010-04-09 15:39:11 -0700601 * the bar struct at foo->bar is held.
602 *
603 * Note that the list of conditions may also include indications of when a lock
604 * need not be held, for example during initialisation or destruction of the
605 * target struct:
606 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700607 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
David Howellsc08c68d2010-04-09 15:39:11 -0700608 * atomic_read(&foo->usage) == 0);
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700609 *
610 * Inserts memory barriers on architectures that require them
611 * (currently only the Alpha), prevents the compiler from refetching
612 * (and from merging fetches), and, more importantly, documents exactly
613 * which pointers are protected by RCU and checks that the pointer is
614 * annotated as __rcu.
Paul E. McKenney632ee202010-02-22 17:04:45 -0800615 */
616#define rcu_dereference_check(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700617 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
Paul E. McKenney632ee202010-02-22 17:04:45 -0800618
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700619/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700620 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
621 * @p: The pointer to read, prior to dereferencing
622 * @c: The conditions under which the dereference will take place
623 *
624 * This is the RCU-bh counterpart to rcu_dereference_check().
625 */
626#define rcu_dereference_bh_check(p, c) \
627 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
628
629/**
630 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
631 * @p: The pointer to read, prior to dereferencing
632 * @c: The conditions under which the dereference will take place
633 *
634 * This is the RCU-sched counterpart to rcu_dereference_check().
635 */
636#define rcu_dereference_sched_check(p, c) \
637 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
638 __rcu)
639
640#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
641
642/**
Paul E. McKenneya4dd9922011-04-01 07:15:14 -0700643 * rcu_access_index() - fetch RCU index with no dereferencing
644 * @p: The index to read
645 *
646 * Return the value of the specified RCU-protected index, but omit the
647 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
648 * when the value of this index is accessed, but the index is not
649 * dereferenced, for example, when testing an RCU-protected index against
650 * -1. Although rcu_access_index() may also be used in cases where
651 * update-side locks prevent the value of the index from changing, you
652 * should instead use rcu_dereference_index_protected() for this use case.
653 */
654#define rcu_access_index(p) __rcu_access_index((p), __rcu)
655
656/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700657 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking
658 * @p: The pointer to read, prior to dereferencing
659 * @c: The conditions under which the dereference will take place
660 *
661 * Similar to rcu_dereference_check(), but omits the sparse checking.
662 * This allows rcu_dereference_index_check() to be used on integers,
663 * which can then be used as array indices. Attempting to use
664 * rcu_dereference_check() on an integer will give compiler warnings
665 * because the sparse address-space mechanism relies on dereferencing
666 * the RCU-protected pointer. Dereferencing integers is not something
667 * that even gcc will put up with.
668 *
669 * Note that this function does not implicitly check for RCU read-side
670 * critical sections. If this function gains lots of uses, it might
671 * make sense to provide versions for each flavor of RCU, but it does
672 * not make sense as of early 2010.
673 */
674#define rcu_dereference_index_check(p, c) \
675 __rcu_dereference_index_check((p), (c))
676
677/**
678 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
679 * @p: The pointer to read, prior to dereferencing
680 * @c: The conditions under which the dereference will take place
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700681 *
682 * Return the value of the specified RCU-protected pointer, but omit
683 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
684 * is useful in cases where update-side locks prevent the value of the
685 * pointer from changing. Please note that this primitive does -not-
686 * prevent the compiler from repeating this reference or combining it
687 * with other references, so it should not be used without protection
688 * of appropriate locks.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700689 *
690 * This function is only for update-side use. Using this function
691 * when protected only by rcu_read_lock() will result in infrequent
692 * but very ugly failures.
Paul E. McKenneyb62730b2010-04-09 15:39:10 -0700693 */
694#define rcu_dereference_protected(p, c) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700695 __rcu_dereference_protected((p), (c), __rcu)
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700696
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700697
698/**
699 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
700 * @p: The pointer to read, prior to dereferencing
701 *
702 * This is a simple wrapper around rcu_dereference_check().
703 */
704#define rcu_dereference(p) rcu_dereference_check(p, 0)
705
706/**
707 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
708 * @p: The pointer to read, prior to dereferencing
709 *
710 * Makes rcu_dereference_check() do the dirty work.
711 */
712#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
713
714/**
715 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
716 * @p: The pointer to read, prior to dereferencing
717 *
718 * Makes rcu_dereference_check() do the dirty work.
719 */
720#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
721
722/**
723 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700724 *
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700725 * When synchronize_rcu() is invoked on one CPU while other CPUs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700726 * are within RCU read-side critical sections, then the
Paul E. McKenney9b06e812005-05-01 08:59:04 -0700727 * synchronize_rcu() is guaranteed to block until after all the other
Linus Torvalds1da177e2005-04-16 15:20:36 -0700728 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
729 * on one CPU while other CPUs are within RCU read-side critical
730 * sections, invocation of the corresponding RCU callback is deferred
731 * until after the all the other CPUs exit their critical sections.
732 *
733 * Note, however, that RCU callbacks are permitted to run concurrently
Paul E. McKenney77d84852010-07-08 17:38:59 -0700734 * with new RCU read-side critical sections. One way that this can happen
Linus Torvalds1da177e2005-04-16 15:20:36 -0700735 * is via the following sequence of events: (1) CPU 0 enters an RCU
736 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
737 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
738 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
739 * callback is invoked. This is legal, because the RCU read-side critical
740 * section that was running concurrently with the call_rcu() (and which
741 * therefore might be referencing something that the corresponding RCU
742 * callback would free up) has completed before the corresponding
743 * RCU callback is invoked.
744 *
745 * RCU read-side critical sections may be nested. Any deferred actions
746 * will be deferred until the outermost RCU read-side critical section
747 * completes.
748 *
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700749 * You can avoid reading and understanding the next paragraph by
750 * following this rule: don't put anything in an rcu_read_lock() RCU
751 * read-side critical section that would block in a !PREEMPT kernel.
752 * But if you want the full story, read on!
753 *
754 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
755 * is illegal to block while in an RCU read-side critical section. In
756 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
757 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
758 * be preempted, but explicit blocking is illegal. Finally, in preemptible
Paul E. McKenney90f45e42013-01-10 05:24:49 -0800759 * RCU implementations in real-time (with -rt patchset) kernel builds,
Paul E. McKenney9079fd72010-08-07 21:59:54 -0700760 * RCU read-side critical sections may be preempted and they may also
761 * block, but only when acquiring spinlocks that are subject to priority
762 * inheritance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700763 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700764static inline void rcu_read_lock(void)
765{
766 __rcu_read_lock();
767 __acquire(RCU);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200768 rcu_lock_acquire(&rcu_lock_map);
Heiko Carstensbde23c62012-02-01 10:30:46 -0800769 rcu_lockdep_assert(!rcu_is_cpu_idle(),
770 "rcu_read_lock() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700771}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700772
Linus Torvalds1da177e2005-04-16 15:20:36 -0700773/*
774 * So where is rcu_write_lock()? It does not exist, as there is no
775 * way for writers to lock out RCU readers. This is a feature, not
776 * a bug -- this property is what provides RCU's performance benefits.
777 * Of course, writers must coordinate with each other. The normal
778 * spinlock primitives work well for this, but any other technique may be
779 * used as well. RCU does not care how the writers keep out of each
780 * others' way, as long as they do so.
781 */
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700782
783/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700784 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
Paul E. McKenney3d76c082009-09-28 07:46:32 -0700785 *
786 * See rcu_read_lock() for more information.
787 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700788static inline void rcu_read_unlock(void)
789{
Heiko Carstensbde23c62012-02-01 10:30:46 -0800790 rcu_lockdep_assert(!rcu_is_cpu_idle(),
791 "rcu_read_unlock() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200792 rcu_lock_release(&rcu_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700793 __release(RCU);
794 __rcu_read_unlock();
795}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700796
797/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700798 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
Linus Torvalds1da177e2005-04-16 15:20:36 -0700799 *
800 * This is equivalent of rcu_read_lock(), but to be used when updates
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700801 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
802 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
803 * softirq handler to be a quiescent state, a process in RCU read-side
804 * critical section must be protected by disabling softirqs. Read-side
805 * critical sections in interrupt context can use just rcu_read_lock(),
806 * though this should at least be commented to avoid confusing people
807 * reading the code.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800808 *
809 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
810 * must occur in the same context, for example, it is illegal to invoke
811 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
812 * was invoked from some other task.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700813 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700814static inline void rcu_read_lock_bh(void)
815{
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700816 local_bh_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700817 __acquire(RCU_BH);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200818 rcu_lock_acquire(&rcu_bh_lock_map);
Heiko Carstensbde23c62012-02-01 10:30:46 -0800819 rcu_lockdep_assert(!rcu_is_cpu_idle(),
820 "rcu_read_lock_bh() used illegally while idle");
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700821}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700822
823/*
824 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
825 *
826 * See rcu_read_lock_bh() for more information.
827 */
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700828static inline void rcu_read_unlock_bh(void)
829{
Heiko Carstensbde23c62012-02-01 10:30:46 -0800830 rcu_lockdep_assert(!rcu_is_cpu_idle(),
831 "rcu_read_unlock_bh() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200832 rcu_lock_release(&rcu_bh_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700833 __release(RCU_BH);
Paul E. McKenney6206ab92011-08-01 06:22:11 -0700834 local_bh_enable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700835}
Linus Torvalds1da177e2005-04-16 15:20:36 -0700836
837/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700838 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400839 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700840 * This is equivalent of rcu_read_lock(), but to be used when updates
841 * are being done using call_rcu_sched() or synchronize_rcu_sched().
842 * Read-side critical sections can also be introduced by anything that
843 * disables preemption, including local_irq_disable() and friends.
Paul E. McKenney3842a082011-11-28 10:42:42 -0800844 *
845 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
846 * must occur in the same context, for example, it is illegal to invoke
847 * rcu_read_unlock_sched() from process context if the matching
848 * rcu_read_lock_sched() was invoked from an NMI handler.
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400849 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700850static inline void rcu_read_lock_sched(void)
851{
852 preempt_disable();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700853 __acquire(RCU_SCHED);
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200854 rcu_lock_acquire(&rcu_sched_lock_map);
Heiko Carstensbde23c62012-02-01 10:30:46 -0800855 rcu_lockdep_assert(!rcu_is_cpu_idle(),
856 "rcu_read_lock_sched() used illegally while idle");
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700857}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700858
859/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700860static inline notrace void rcu_read_lock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700861{
862 preempt_disable_notrace();
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700863 __acquire(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700864}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400865
866/*
867 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
868 *
869 * See rcu_read_lock_sched for more information.
870 */
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700871static inline void rcu_read_unlock_sched(void)
872{
Heiko Carstensbde23c62012-02-01 10:30:46 -0800873 rcu_lockdep_assert(!rcu_is_cpu_idle(),
874 "rcu_read_unlock_sched() used illegally while idle");
Paul E. McKenneyd8ab29f2011-10-07 18:22:03 +0200875 rcu_lock_release(&rcu_sched_lock_map);
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700876 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700877 preempt_enable();
878}
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700879
880/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
Paul E. McKenney7c614d62009-08-24 09:42:00 -0700881static inline notrace void rcu_read_unlock_sched_notrace(void)
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700882{
Paul E. McKenneybc33f242009-08-22 13:56:47 -0700883 __release(RCU_SCHED);
Paul E. McKenneyd6714c22009-08-22 13:56:46 -0700884 preempt_enable_notrace();
885}
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400886
Mathieu Desnoyers1c50b722008-09-29 11:06:46 -0400887/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700888 * rcu_assign_pointer() - assign to RCU-protected pointer
889 * @p: pointer to assign to
890 * @v: value to assign (publish)
Paul E. McKenneyc26d34a2010-02-22 17:04:46 -0800891 *
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700892 * Assigns the specified value to the specified RCU-protected
893 * pointer, ensuring that any concurrent RCU readers will see
Paul E. McKenneye9023c42012-05-16 15:51:08 -0700894 * any prior initialization.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700895 *
896 * Inserts memory barriers on architectures that require them
Paul E. McKenney6846c0c2011-07-31 22:33:02 -0700897 * (which is most of them), and also prevents the compiler from
898 * reordering the code that initializes the structure after the pointer
899 * assignment. More importantly, this call documents which pointers
900 * will be dereferenced by RCU read-side code.
901 *
902 * In some special cases, you may use RCU_INIT_POINTER() instead
903 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
904 * to the fact that it does not constrain either the CPU or the compiler.
905 * That said, using RCU_INIT_POINTER() when you should have used
906 * rcu_assign_pointer() is a very bad thing that results in
907 * impossible-to-diagnose memory corruption. So please be careful.
908 * See the RCU_INIT_POINTER() comment header for details.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700909 */
Paul E. McKenneyd99c4f62008-02-06 01:37:25 -0800910#define rcu_assign_pointer(p, v) \
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700911 __rcu_assign_pointer((p), (v), __rcu)
912
913/**
914 * RCU_INIT_POINTER() - initialize an RCU protected pointer
915 *
Paul E. McKenney6846c0c2011-07-31 22:33:02 -0700916 * Initialize an RCU-protected pointer in special cases where readers
917 * do not need ordering constraints on the CPU or the compiler. These
918 * special cases are:
919 *
920 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
921 * 2. The caller has taken whatever steps are required to prevent
922 * RCU readers from concurrently accessing this pointer -or-
923 * 3. The referenced data structure has already been exposed to
924 * readers either at compile time or via rcu_assign_pointer() -and-
925 * a. You have not made -any- reader-visible changes to
926 * this structure since then -or-
927 * b. It is OK for readers accessing this structure from its
928 * new location to see the old state of the structure. (For
929 * example, the changes were to statistical counters or to
930 * other state where exact synchronization is not required.)
931 *
932 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
933 * result in impossible-to-diagnose memory corruption. As in the structures
934 * will look OK in crash dumps, but any concurrent RCU readers might
935 * see pre-initialized values of the referenced data structure. So
936 * please be very careful how you use RCU_INIT_POINTER()!!!
937 *
938 * If you are creating an RCU-protected linked structure that is accessed
939 * by a single external-to-structure RCU-protected pointer, then you may
940 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
941 * pointers, but you must use rcu_assign_pointer() to initialize the
942 * external-to-structure pointer -after- you have completely initialized
943 * the reader-accessible portions of the linked structure.
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -0700944 */
945#define RCU_INIT_POINTER(p, v) \
Paul E. McKenneyd1b88eb2012-05-16 15:42:30 -0700946 do { \
947 p = (typeof(*v) __force __rcu *)(v); \
948 } while (0)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700949
Paul E. McKenney172708d2012-05-16 15:23:45 -0700950/**
951 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
952 *
953 * GCC-style initialization for an RCU-protected pointer in a structure field.
954 */
955#define RCU_POINTER_INITIALIZER(p, v) \
956 .p = (typeof(*v) __force __rcu *)(v)
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800957
Jan Engelhardtd8169d42012-04-19 11:44:39 -0700958/*
959 * Does the specified offset indicate that the corresponding rcu_head
960 * structure can be handled by kfree_rcu()?
961 */
962#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
963
964/*
965 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
966 */
967#define __kfree_rcu(head, offset) \
968 do { \
969 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
Paul E. McKenney4fa3b6c2012-06-05 15:53:53 -0700970 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
Jan Engelhardtd8169d42012-04-19 11:44:39 -0700971 } while (0)
972
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800973/**
974 * kfree_rcu() - kfree an object after a grace period.
975 * @ptr: pointer to kfree
976 * @rcu_head: the name of the struct rcu_head within the type of @ptr.
977 *
978 * Many rcu callbacks functions just call kfree() on the base structure.
979 * These functions are trivial, but their size adds up, and furthermore
980 * when they are used in a kernel module, that module must invoke the
981 * high-latency rcu_barrier() function at module-unload time.
982 *
983 * The kfree_rcu() function handles this issue. Rather than encoding a
984 * function address in the embedded rcu_head structure, kfree_rcu() instead
985 * encodes the offset of the rcu_head structure within the base structure.
986 * Because the functions are not allowed in the low-order 4096 bytes of
987 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
988 * If the offset is larger than 4095 bytes, a compile-time error will
989 * be generated in __kfree_rcu(). If this error is triggered, you can
990 * either fall back to use of call_rcu() or rearrange the structure to
991 * position the rcu_head structure into the first 4096 bytes.
992 *
993 * Note that the allowable offset might decrease in the future, for example,
994 * to allow something like kmem_cache_free_rcu().
Jan Engelhardtd8169d42012-04-19 11:44:39 -0700995 *
996 * The BUILD_BUG_ON check must not involve any function calls, hence the
997 * checks are done in macros here.
Lai Jiangshan9ab15442011-03-18 11:15:47 +0800998 */
999#define kfree_rcu(ptr, rcu_head) \
1000 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
1001
Linus Torvalds1da177e2005-04-16 15:20:36 -07001002#endif /* __LINUX_RCUPDATE_H */