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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>
40#include <asm/atomic.h>
41#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 E. McKenney01c1c662008-01-25 21:08:24 +010046#include <linux/module.h>
Paul E. McKenneya6826042009-02-25 18:03:42 -080047#include <linux/kernel_stat.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070048
Paul E. McKenney70f12f82008-05-12 21:21:05 +020049enum rcu_barrier {
50 RCU_BARRIER_STD,
51 RCU_BARRIER_BH,
52 RCU_BARRIER_SCHED,
53};
54
Paul E. McKenney01c1c662008-01-25 21:08:24 +010055static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
Dipankar Sarma21a1ea92006-03-07 21:55:33 -080056static atomic_t rcu_barrier_cpu_count;
Ingo Molnar9331b312006-03-23 03:00:19 -080057static DEFINE_MUTEX(rcu_barrier_mutex);
Dipankar Sarma21a1ea92006-03-07 21:55:33 -080058static struct completion rcu_barrier_completion;
Paul E. McKenneya6826042009-02-25 18:03:42 -080059int rcu_scheduler_active __read_mostly;
Dipankar Sarma21a1ea92006-03-07 21:55:33 -080060
David Howells5b1d07e2009-04-15 19:35:01 +010061static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
62static struct rcu_head rcu_migrate_head[3];
63static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
64
Paul E. McKenneyfbf6bfc2008-02-13 15:03:15 -080065/*
66 * Awaken the corresponding synchronize_rcu() instance now that a
67 * grace period has elapsed.
68 */
Paul E. McKenney4446a362008-05-12 21:21:05 +020069void wakeme_after_rcu(struct rcu_head *head)
Dipankar Sarma21a1ea92006-03-07 21:55:33 -080070{
Paul E. McKenney01c1c662008-01-25 21:08:24 +010071 struct rcu_synchronize *rcu;
72
73 rcu = container_of(head, struct rcu_synchronize, head);
74 complete(&rcu->completion);
Dipankar Sarma21a1ea92006-03-07 21:55:33 -080075}
Linus Torvalds1da177e2005-04-16 15:20:36 -070076
Paul E. McKenney16e30812009-09-13 09:15:11 -070077#ifdef CONFIG_TREE_PREEMPT_RCU
78
Linus Torvalds1da177e2005-04-16 15:20:36 -070079/**
Paul E. McKenney01c1c662008-01-25 21:08:24 +010080 * synchronize_rcu - wait until a grace period has elapsed.
Linus Torvalds1da177e2005-04-16 15:20:36 -070081 *
Paul E. McKenney01c1c662008-01-25 21:08:24 +010082 * Control will return to the caller some time after a full grace
83 * period has elapsed, in other words after all currently executing RCU
Linus Torvalds1da177e2005-04-16 15:20:36 -070084 * read-side critical sections have completed. RCU read-side critical
85 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
86 * and may be nested.
87 */
Paul E. McKenneyea7d3fe2009-01-04 13:03:02 -080088void synchronize_rcu(void)
89{
90 struct rcu_synchronize rcu;
Paul E. McKenneya6826042009-02-25 18:03:42 -080091
Paul E. McKenney16e30812009-09-13 09:15:11 -070092 if (!rcu_scheduler_active)
Paul E. McKenneya6826042009-02-25 18:03:42 -080093 return;
94
Paul E. McKenneyea7d3fe2009-01-04 13:03:02 -080095 init_completion(&rcu.completion);
96 /* Will wake me after RCU finished. */
97 call_rcu(&rcu.head, wakeme_after_rcu);
98 /* Wait for it. */
99 wait_for_completion(&rcu.completion);
100}
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100101EXPORT_SYMBOL_GPL(synchronize_rcu);
Paul E. McKenneyc32e0662006-06-27 02:54:04 -0700102
Paul E. McKenney16e30812009-09-13 09:15:11 -0700103#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
104
105/**
106 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
107 *
108 * Control will return to the caller some time after a full rcu-sched
109 * grace period has elapsed, in other words after all currently executing
110 * rcu-sched read-side critical sections have completed. These read-side
111 * critical sections are delimited by rcu_read_lock_sched() and
112 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
113 * local_irq_disable(), and so on may be used in place of
114 * rcu_read_lock_sched().
115 *
116 * This means that all preempt_disable code sequences, including NMI and
117 * hardware-interrupt handlers, in progress on entry will have completed
118 * before this primitive returns. However, this does not guarantee that
119 * softirq handlers will have completed, since in some kernels, these
120 * handlers can run in process context, and can block.
121 *
122 * This primitive provides the guarantees made by the (now removed)
123 * synchronize_kernel() API. In contrast, synchronize_rcu() only
124 * guarantees that rcu_read_lock() sections will have completed.
125 * In "classic RCU", these two guarantees happen to be one and
126 * the same, but can differ in realtime RCU implementations.
127 */
128void synchronize_sched(void)
129{
130 struct rcu_synchronize rcu;
131
132 if (rcu_blocking_is_gp())
133 return;
134
135 init_completion(&rcu.completion);
136 /* Will wake me after RCU finished. */
137 call_rcu_sched(&rcu.head, wakeme_after_rcu);
138 /* Wait for it. */
139 wait_for_completion(&rcu.completion);
140}
141EXPORT_SYMBOL_GPL(synchronize_sched);
142
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700143/**
144 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
145 *
146 * Control will return to the caller some time after a full rcu_bh grace
147 * period has elapsed, in other words after all currently executing rcu_bh
148 * read-side critical sections have completed. RCU read-side critical
149 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
150 * and may be nested.
151 */
152void synchronize_rcu_bh(void)
153{
154 struct rcu_synchronize rcu;
155
156 if (rcu_blocking_is_gp())
157 return;
158
159 init_completion(&rcu.completion);
160 /* Will wake me after RCU finished. */
161 call_rcu_bh(&rcu.head, wakeme_after_rcu);
162 /* Wait for it. */
163 wait_for_completion(&rcu.completion);
164}
165EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
166
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800167static void rcu_barrier_callback(struct rcu_head *notused)
168{
169 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
170 complete(&rcu_barrier_completion);
171}
172
173/*
174 * Called with preemption disabled, and from cross-cpu IRQ context.
175 */
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200176static void rcu_barrier_func(void *type)
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800177{
178 int cpu = smp_processor_id();
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100179 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800180
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800181 atomic_inc(&rcu_barrier_cpu_count);
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200182 switch ((enum rcu_barrier)type) {
183 case RCU_BARRIER_STD:
184 call_rcu(head, rcu_barrier_callback);
185 break;
186 case RCU_BARRIER_BH:
187 call_rcu_bh(head, rcu_barrier_callback);
188 break;
189 case RCU_BARRIER_SCHED:
190 call_rcu_sched(head, rcu_barrier_callback);
191 break;
192 }
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800193}
194
David Howells5b1d07e2009-04-15 19:35:01 +0100195static inline void wait_migrated_callbacks(void)
196{
197 wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
Paul E. McKenney03b042b2009-06-25 09:08:16 -0700198 smp_mb(); /* In case we didn't sleep. */
David Howells5b1d07e2009-04-15 19:35:01 +0100199}
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800200
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200201/*
202 * Orchestrate the specified type of RCU barrier, waiting for all
203 * RCU callbacks of the specified type to complete.
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800204 */
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200205static void _rcu_barrier(enum rcu_barrier type)
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800206{
207 BUG_ON(in_interrupt());
Ingo Molnar9331b312006-03-23 03:00:19 -0800208 /* Take cpucontrol mutex to protect against CPU hotplug */
209 mutex_lock(&rcu_barrier_mutex);
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800210 init_completion(&rcu_barrier_completion);
Paul E. McKenneye0ecfa72008-01-25 21:08:24 +0100211 /*
Lai Jiangshan5f865152008-10-17 14:40:30 +0800212 * Initialize rcu_barrier_cpu_count to 1, then invoke
213 * rcu_barrier_func() on each CPU, so that each CPU also has
214 * incremented rcu_barrier_cpu_count. Only then is it safe to
215 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
216 * might complete its grace period before all of the other CPUs
217 * did their increment, causing this function to return too
218 * early.
Paul E. McKenneye0ecfa72008-01-25 21:08:24 +0100219 */
Lai Jiangshan5f865152008-10-17 14:40:30 +0800220 atomic_set(&rcu_barrier_cpu_count, 1);
Linus Torvalds59190f42008-07-15 14:02:33 -0700221 on_each_cpu(rcu_barrier_func, (void *)type, 1);
Lai Jiangshan5f865152008-10-17 14:40:30 +0800222 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
223 complete(&rcu_barrier_completion);
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800224 wait_for_completion(&rcu_barrier_completion);
Ingo Molnar9331b312006-03-23 03:00:19 -0800225 mutex_unlock(&rcu_barrier_mutex);
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800226 wait_migrated_callbacks();
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800227}
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200228
229/**
230 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
231 */
232void rcu_barrier(void)
233{
234 _rcu_barrier(RCU_BARRIER_STD);
235}
Dipankar Sarmaab4720e2005-12-12 00:37:05 -0800236EXPORT_SYMBOL_GPL(rcu_barrier);
237
Paul E. McKenney70f12f82008-05-12 21:21:05 +0200238/**
239 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
240 */
241void rcu_barrier_bh(void)
242{
243 _rcu_barrier(RCU_BARRIER_BH);
244}
245EXPORT_SYMBOL_GPL(rcu_barrier_bh);
246
247/**
248 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
249 */
250void rcu_barrier_sched(void)
251{
252 _rcu_barrier(RCU_BARRIER_SCHED);
253}
254EXPORT_SYMBOL_GPL(rcu_barrier_sched);
255
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800256static void rcu_migrate_callback(struct rcu_head *notused)
257{
258 if (atomic_dec_and_test(&rcu_migrate_type_count))
259 wake_up(&rcu_migrate_wq);
260}
261
Paul E. McKenney2e597552009-08-15 09:53:48 -0700262extern int rcu_cpu_notify(struct notifier_block *self,
263 unsigned long action, void *hcpu);
264
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800265static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
266 unsigned long action, void *hcpu)
267{
Paul E. McKenney2e597552009-08-15 09:53:48 -0700268 rcu_cpu_notify(self, action, hcpu);
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800269 if (action == CPU_DYING) {
270 /*
271 * preempt_disable() in on_each_cpu() prevents stop_machine(),
272 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
273 * returns, all online cpus have queued rcu_barrier_func(),
274 * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
275 *
276 * These callbacks ensure _rcu_barrier() waits for all
277 * RCU callbacks of the specified type to complete.
278 */
279 atomic_set(&rcu_migrate_type_count, 3);
280 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
281 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
282 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
Paul E. McKenney1423cc02009-08-18 23:06:14 -0700283 } else if (action == CPU_DOWN_PREPARE) {
284 /* Don't need to wait until next removal operation. */
Lai Jiangshanf69b17d2009-03-20 17:40:06 +0800285 /* rcu_migrate_head is protected by cpu_add_remove_lock */
286 wait_migrated_callbacks();
287 }
288
289 return NOTIFY_OK;
290}
291
Linus Torvalds1da177e2005-04-16 15:20:36 -0700292void __init rcu_init(void)
293{
Paul E. McKenney2e597552009-08-15 09:53:48 -0700294 int i;
295
Paul E. McKenney01c1c662008-01-25 21:08:24 +0100296 __rcu_init();
Paul E. McKenney2e597552009-08-15 09:53:48 -0700297 cpu_notifier(rcu_barrier_cpu_hotplug, 0);
298
299 /*
300 * We don't need protection against CPU-hotplug here because
301 * this is called early in boot, before either interrupts
302 * or the scheduler are operational.
303 */
304 for_each_online_cpu(i)
305 rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700306}
307
Paul E. McKenneya6826042009-02-25 18:03:42 -0800308void rcu_scheduler_starting(void)
309{
310 WARN_ON(num_online_cpus() != 1);
311 WARN_ON(nr_context_switches() > 0);
312 rcu_scheduler_active = 1;
313}