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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
Paul E. McKenney01c1c662008-01-25 21:08:24 +010018 * Copyright IBM Corporation, 2001
Linus Torvalds1da177e2005-04-16 15:20:36 -070019 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
Paul E. McKenneya71fca52009-09-18 10:28:19 -070022 *
Linus Torvalds1da177e2005-04-16 15:20:36 -070023 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * Papers:
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 *
29 * For detailed explanation of Read-Copy Update mechanism see -
Paul E. McKenneya71fca52009-09-18 10:28:19 -070030 * http://lse.sourceforge.net/locking/rcupdate.html
Linus Torvalds1da177e2005-04-16 15:20:36 -070031 *
32 */
33#include <linux/types.h>
34#include <linux/kernel.h>
35#include <linux/init.h>
36#include <linux/spinlock.h>
37#include <linux/smp.h>
38#include <linux/interrupt.h>
39#include <linux/sched.h>
Arun Sharma600634972011-07-26 16:09:06 -070040#include <linux/atomic.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070041#include <linux/bitops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070042#include <linux/percpu.h>
43#include <linux/notifier.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070044#include <linux/cpu.h>
Ingo Molnar9331b312006-03-23 03:00:19 -080045#include <linux/mutex.h>
Paul Gortmaker9984de12011-05-23 14:51:41 -040046#include <linux/export.h>
Paul E. McKenneye3818b82010-03-15 17:03:43 -070047#include <linux/hardirq.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070048
Paul E. McKenney29c00b42011-06-17 15:53:19 -070049#define CREATE_TRACE_POINTS
50#include <trace/events/rcu.h>
51
52#include "rcu.h"
53
Paul E. McKenney162cc272009-09-23 16:18:13 -070054#ifdef CONFIG_DEBUG_LOCK_ALLOC
55static struct lock_class_key rcu_lock_key;
56struct lockdep_map rcu_lock_map =
57 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
58EXPORT_SYMBOL_GPL(rcu_lock_map);
Paul E. McKenney632ee202010-02-22 17:04:45 -080059
60static struct lock_class_key rcu_bh_lock_key;
61struct lockdep_map rcu_bh_lock_map =
62 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
63EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
64
65static struct lock_class_key rcu_sched_lock_key;
66struct lockdep_map rcu_sched_lock_map =
67 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
68EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
Paul E. McKenney162cc272009-09-23 16:18:13 -070069#endif
70
Paul E. McKenneye3818b82010-03-15 17:03:43 -070071#ifdef CONFIG_DEBUG_LOCK_ALLOC
72
Paul E. McKenneybc293d62010-04-15 12:50:39 -070073int debug_lockdep_rcu_enabled(void)
74{
75 return rcu_scheduler_active && debug_locks &&
76 current->lockdep_recursion == 0;
77}
78EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
79
Paul E. McKenneye3818b82010-03-15 17:03:43 -070080/**
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -070081 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
Paul E. McKenneye3818b82010-03-15 17:03:43 -070082 *
83 * Check for bottom half being disabled, which covers both the
84 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
85 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
Paul E. McKenneyca5ecdd2010-04-28 14:39:09 -070086 * will show the situation. This is useful for debug checks in functions
87 * that require that they be called within an RCU read-side critical
88 * section.
Paul E. McKenneye3818b82010-03-15 17:03:43 -070089 *
90 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
91 */
92int rcu_read_lock_bh_held(void)
93{
94 if (!debug_lockdep_rcu_enabled())
95 return 1;
Paul E. McKenney773e3f92010-10-05 14:03:02 -070096 return in_softirq() || irqs_disabled();
Paul E. McKenneye3818b82010-03-15 17:03:43 -070097}
98EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
99
100#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
101
Paul E. McKenney2c428182011-05-26 22:14:36 -0700102struct rcu_synchronize {
103 struct rcu_head head;
104 struct completion completion;
105};
106
Paul E. McKenneyd9f1bb62010-02-25 14:06:47 -0800107/*
Paul E. McKenneyfbf6bfc2008-02-13 15:03:15 -0800108 * Awaken the corresponding synchronize_rcu() instance now that a
109 * grace period has elapsed.
110 */
Paul E. McKenney2c428182011-05-26 22:14:36 -0700111static void wakeme_after_rcu(struct rcu_head *head)
Dipankar Sarma21a1ea92006-03-07 21:55:33 -0800112{
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100113 struct rcu_synchronize *rcu;
114
115 rcu = container_of(head, struct rcu_synchronize, head);
116 complete(&rcu->completion);
Dipankar Sarma21a1ea92006-03-07 21:55:33 -0800117}
Paul E. McKenneyee84b822010-05-06 09:28:41 -0700118
Paul E. McKenney2c428182011-05-26 22:14:36 -0700119void wait_rcu_gp(call_rcu_func_t crf)
120{
121 struct rcu_synchronize rcu;
122
123 init_rcu_head_on_stack(&rcu.head);
124 init_completion(&rcu.completion);
125 /* Will wake me after RCU finished. */
126 crf(&rcu.head, wakeme_after_rcu);
127 /* Wait for it. */
128 wait_for_completion(&rcu.completion);
129 destroy_rcu_head_on_stack(&rcu.head);
130}
131EXPORT_SYMBOL_GPL(wait_rcu_gp);
132
Paul E. McKenneyee84b822010-05-06 09:28:41 -0700133#ifdef CONFIG_PROVE_RCU
134/*
135 * wrapper function to avoid #include problems.
136 */
137int rcu_my_thread_group_empty(void)
138{
139 return thread_group_empty(current);
140}
141EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
142#endif /* #ifdef CONFIG_PROVE_RCU */
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400143
144#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
145static inline void debug_init_rcu_head(struct rcu_head *head)
146{
147 debug_object_init(head, &rcuhead_debug_descr);
148}
149
150static inline void debug_rcu_head_free(struct rcu_head *head)
151{
152 debug_object_free(head, &rcuhead_debug_descr);
153}
154
155/*
156 * fixup_init is called when:
157 * - an active object is initialized
158 */
159static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
160{
161 struct rcu_head *head = addr;
162
163 switch (state) {
164 case ODEBUG_STATE_ACTIVE:
165 /*
166 * Ensure that queued callbacks are all executed.
167 * If we detect that we are nested in a RCU read-side critical
168 * section, we should simply fail, otherwise we would deadlock.
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800169 * In !PREEMPT configurations, there is no way to tell if we are
170 * in a RCU read-side critical section or not, so we never
171 * attempt any fixup and just print a warning.
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400172 */
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800173#ifndef CONFIG_PREEMPT
Paul E. McKenney108aae22011-02-23 09:56:00 -0800174 WARN_ON_ONCE(1);
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800175 return 0;
176#endif
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400177 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
178 irqs_disabled()) {
Paul E. McKenney108aae22011-02-23 09:56:00 -0800179 WARN_ON_ONCE(1);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400180 return 0;
181 }
182 rcu_barrier();
183 rcu_barrier_sched();
184 rcu_barrier_bh();
185 debug_object_init(head, &rcuhead_debug_descr);
186 return 1;
187 default:
188 return 0;
189 }
190}
191
192/*
193 * fixup_activate is called when:
194 * - an active object is activated
195 * - an unknown object is activated (might be a statically initialized object)
196 * Activation is performed internally by call_rcu().
197 */
198static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
199{
200 struct rcu_head *head = addr;
201
202 switch (state) {
203
204 case ODEBUG_STATE_NOTAVAILABLE:
205 /*
206 * This is not really a fixup. We just make sure that it is
207 * tracked in the object tracker.
208 */
209 debug_object_init(head, &rcuhead_debug_descr);
210 debug_object_activate(head, &rcuhead_debug_descr);
211 return 0;
212
213 case ODEBUG_STATE_ACTIVE:
214 /*
215 * Ensure that queued callbacks are all executed.
216 * If we detect that we are nested in a RCU read-side critical
217 * section, we should simply fail, otherwise we would deadlock.
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800218 * In !PREEMPT configurations, there is no way to tell if we are
219 * in a RCU read-side critical section or not, so we never
220 * attempt any fixup and just print a warning.
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400221 */
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800222#ifndef CONFIG_PREEMPT
Paul E. McKenney108aae22011-02-23 09:56:00 -0800223 WARN_ON_ONCE(1);
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800224 return 0;
225#endif
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400226 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
227 irqs_disabled()) {
Paul E. McKenney108aae22011-02-23 09:56:00 -0800228 WARN_ON_ONCE(1);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400229 return 0;
230 }
231 rcu_barrier();
232 rcu_barrier_sched();
233 rcu_barrier_bh();
234 debug_object_activate(head, &rcuhead_debug_descr);
235 return 1;
236 default:
237 return 0;
238 }
239}
240
241/*
242 * fixup_free is called when:
243 * - an active object is freed
244 */
245static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
246{
247 struct rcu_head *head = addr;
248
249 switch (state) {
250 case ODEBUG_STATE_ACTIVE:
251 /*
252 * Ensure that queued callbacks are all executed.
253 * If we detect that we are nested in a RCU read-side critical
254 * section, we should simply fail, otherwise we would deadlock.
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800255 * In !PREEMPT configurations, there is no way to tell if we are
256 * in a RCU read-side critical section or not, so we never
257 * attempt any fixup and just print a warning.
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400258 */
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800259#ifndef CONFIG_PREEMPT
Paul E. McKenney108aae22011-02-23 09:56:00 -0800260 WARN_ON_ONCE(1);
Mathieu Desnoyersfc2ecf72011-02-23 09:42:14 -0800261 return 0;
262#endif
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400263 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
264 irqs_disabled()) {
Paul E. McKenney108aae22011-02-23 09:56:00 -0800265 WARN_ON_ONCE(1);
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400266 return 0;
267 }
268 rcu_barrier();
269 rcu_barrier_sched();
270 rcu_barrier_bh();
271 debug_object_free(head, &rcuhead_debug_descr);
272 return 1;
Mathieu Desnoyers551d55a2010-04-17 08:48:42 -0400273 default:
274 return 0;
275 }
276}
277
278/**
279 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
280 * @head: pointer to rcu_head structure to be initialized
281 *
282 * This function informs debugobjects of a new rcu_head structure that
283 * has been allocated as an auto variable on the stack. This function
284 * is not required for rcu_head structures that are statically defined or
285 * that are dynamically allocated on the heap. This function has no
286 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
287 */
288void init_rcu_head_on_stack(struct rcu_head *head)
289{
290 debug_object_init_on_stack(head, &rcuhead_debug_descr);
291}
292EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
293
294/**
295 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
296 * @head: pointer to rcu_head structure to be initialized
297 *
298 * This function informs debugobjects that an on-stack rcu_head structure
299 * is about to go out of scope. As with init_rcu_head_on_stack(), this
300 * function is not required for rcu_head structures that are statically
301 * defined or that are dynamically allocated on the heap. Also as with
302 * init_rcu_head_on_stack(), this function has no effect for
303 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
304 */
305void destroy_rcu_head_on_stack(struct rcu_head *head)
306{
307 debug_object_free(head, &rcuhead_debug_descr);
308}
309EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
310
311struct debug_obj_descr rcuhead_debug_descr = {
312 .name = "rcu_head",
313 .fixup_init = rcuhead_fixup_init,
314 .fixup_activate = rcuhead_fixup_activate,
315 .fixup_free = rcuhead_fixup_free,
316};
317EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
318#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */