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1da177e4 LT |
1 | /* |
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 | * | |
01c1c660 | 18 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
19 | * |
20 | * Authors: Dipankar Sarma <dipankar@in.ibm.com> | |
21 | * Manfred Spraul <manfred@colorfullife.com> | |
22 | * | |
23 | * 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 - | |
30 | * http://lse.sourceforge.net/locking/rcupdate.html | |
31 | * | |
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> | |
1da177e4 LT |
42 | #include <linux/percpu.h> |
43 | #include <linux/notifier.h> | |
1da177e4 | 44 | #include <linux/cpu.h> |
9331b315 | 45 | #include <linux/mutex.h> |
01c1c660 | 46 | #include <linux/module.h> |
a6826048 | 47 | #include <linux/kernel_stat.h> |
1da177e4 | 48 | |
70f12f84 PM |
49 | enum rcu_barrier { |
50 | RCU_BARRIER_STD, | |
51 | RCU_BARRIER_BH, | |
52 | RCU_BARRIER_SCHED, | |
53 | }; | |
54 | ||
01c1c660 | 55 | static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL}; |
21a1ea9e | 56 | static atomic_t rcu_barrier_cpu_count; |
9331b315 | 57 | static DEFINE_MUTEX(rcu_barrier_mutex); |
21a1ea9e | 58 | static struct completion rcu_barrier_completion; |
a6826048 | 59 | int rcu_scheduler_active __read_mostly; |
21a1ea9e | 60 | |
5b1d07ed DH |
61 | static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0); |
62 | static struct rcu_head rcu_migrate_head[3]; | |
63 | static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq); | |
64 | ||
fbf6bfca PM |
65 | /* |
66 | * Awaken the corresponding synchronize_rcu() instance now that a | |
67 | * grace period has elapsed. | |
68 | */ | |
4446a36f | 69 | void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 70 | { |
01c1c660 PM |
71 | struct rcu_synchronize *rcu; |
72 | ||
73 | rcu = container_of(head, struct rcu_synchronize, head); | |
74 | complete(&rcu->completion); | |
21a1ea9e | 75 | } |
1da177e4 LT |
76 | |
77 | /** | |
01c1c660 | 78 | * synchronize_rcu - wait until a grace period has elapsed. |
1da177e4 | 79 | * |
01c1c660 PM |
80 | * Control will return to the caller some time after a full grace |
81 | * period has elapsed, in other words after all currently executing RCU | |
1da177e4 LT |
82 | * read-side critical sections have completed. RCU read-side critical |
83 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
84 | * and may be nested. | |
85 | */ | |
ea7d3fef PM |
86 | void synchronize_rcu(void) |
87 | { | |
88 | struct rcu_synchronize rcu; | |
a6826048 PM |
89 | |
90 | if (rcu_blocking_is_gp()) | |
91 | return; | |
92 | ||
ea7d3fef PM |
93 | init_completion(&rcu.completion); |
94 | /* Will wake me after RCU finished. */ | |
95 | call_rcu(&rcu.head, wakeme_after_rcu); | |
96 | /* Wait for it. */ | |
97 | wait_for_completion(&rcu.completion); | |
98 | } | |
01c1c660 | 99 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
c32e0660 | 100 | |
03b042bf PM |
101 | /** |
102 | * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. | |
103 | * | |
104 | * Control will return to the caller some time after a full rcu_bh grace | |
105 | * period has elapsed, in other words after all currently executing rcu_bh | |
106 | * read-side critical sections have completed. RCU read-side critical | |
107 | * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(), | |
108 | * and may be nested. | |
109 | */ | |
110 | void synchronize_rcu_bh(void) | |
111 | { | |
112 | struct rcu_synchronize rcu; | |
113 | ||
114 | if (rcu_blocking_is_gp()) | |
115 | return; | |
116 | ||
117 | init_completion(&rcu.completion); | |
118 | /* Will wake me after RCU finished. */ | |
119 | call_rcu_bh(&rcu.head, wakeme_after_rcu); | |
120 | /* Wait for it. */ | |
121 | wait_for_completion(&rcu.completion); | |
122 | } | |
123 | EXPORT_SYMBOL_GPL(synchronize_rcu_bh); | |
124 | ||
ab4720ec DS |
125 | static void rcu_barrier_callback(struct rcu_head *notused) |
126 | { | |
127 | if (atomic_dec_and_test(&rcu_barrier_cpu_count)) | |
128 | complete(&rcu_barrier_completion); | |
129 | } | |
130 | ||
131 | /* | |
132 | * Called with preemption disabled, and from cross-cpu IRQ context. | |
133 | */ | |
70f12f84 | 134 | static void rcu_barrier_func(void *type) |
ab4720ec DS |
135 | { |
136 | int cpu = smp_processor_id(); | |
01c1c660 | 137 | struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu); |
ab4720ec | 138 | |
ab4720ec | 139 | atomic_inc(&rcu_barrier_cpu_count); |
70f12f84 PM |
140 | switch ((enum rcu_barrier)type) { |
141 | case RCU_BARRIER_STD: | |
142 | call_rcu(head, rcu_barrier_callback); | |
143 | break; | |
144 | case RCU_BARRIER_BH: | |
145 | call_rcu_bh(head, rcu_barrier_callback); | |
146 | break; | |
147 | case RCU_BARRIER_SCHED: | |
148 | call_rcu_sched(head, rcu_barrier_callback); | |
149 | break; | |
150 | } | |
ab4720ec DS |
151 | } |
152 | ||
5b1d07ed DH |
153 | static inline void wait_migrated_callbacks(void) |
154 | { | |
155 | wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count)); | |
03b042bf | 156 | smp_mb(); /* In case we didn't sleep. */ |
5b1d07ed | 157 | } |
f69b17d7 | 158 | |
70f12f84 PM |
159 | /* |
160 | * Orchestrate the specified type of RCU barrier, waiting for all | |
161 | * RCU callbacks of the specified type to complete. | |
ab4720ec | 162 | */ |
70f12f84 | 163 | static void _rcu_barrier(enum rcu_barrier type) |
ab4720ec DS |
164 | { |
165 | BUG_ON(in_interrupt()); | |
9331b315 IM |
166 | /* Take cpucontrol mutex to protect against CPU hotplug */ |
167 | mutex_lock(&rcu_barrier_mutex); | |
ab4720ec | 168 | init_completion(&rcu_barrier_completion); |
e0ecfa79 | 169 | /* |
5f865151 LJ |
170 | * Initialize rcu_barrier_cpu_count to 1, then invoke |
171 | * rcu_barrier_func() on each CPU, so that each CPU also has | |
172 | * incremented rcu_barrier_cpu_count. Only then is it safe to | |
173 | * decrement rcu_barrier_cpu_count -- otherwise the first CPU | |
174 | * might complete its grace period before all of the other CPUs | |
175 | * did their increment, causing this function to return too | |
176 | * early. | |
e0ecfa79 | 177 | */ |
5f865151 | 178 | atomic_set(&rcu_barrier_cpu_count, 1); |
59190f42 | 179 | on_each_cpu(rcu_barrier_func, (void *)type, 1); |
5f865151 LJ |
180 | if (atomic_dec_and_test(&rcu_barrier_cpu_count)) |
181 | complete(&rcu_barrier_completion); | |
ab4720ec | 182 | wait_for_completion(&rcu_barrier_completion); |
9331b315 | 183 | mutex_unlock(&rcu_barrier_mutex); |
f69b17d7 | 184 | wait_migrated_callbacks(); |
ab4720ec | 185 | } |
70f12f84 PM |
186 | |
187 | /** | |
188 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
189 | */ | |
190 | void rcu_barrier(void) | |
191 | { | |
192 | _rcu_barrier(RCU_BARRIER_STD); | |
193 | } | |
ab4720ec DS |
194 | EXPORT_SYMBOL_GPL(rcu_barrier); |
195 | ||
70f12f84 PM |
196 | /** |
197 | * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. | |
198 | */ | |
199 | void rcu_barrier_bh(void) | |
200 | { | |
201 | _rcu_barrier(RCU_BARRIER_BH); | |
202 | } | |
203 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); | |
204 | ||
205 | /** | |
206 | * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. | |
207 | */ | |
208 | void rcu_barrier_sched(void) | |
209 | { | |
210 | _rcu_barrier(RCU_BARRIER_SCHED); | |
211 | } | |
212 | EXPORT_SYMBOL_GPL(rcu_barrier_sched); | |
213 | ||
f69b17d7 LJ |
214 | static void rcu_migrate_callback(struct rcu_head *notused) |
215 | { | |
216 | if (atomic_dec_and_test(&rcu_migrate_type_count)) | |
217 | wake_up(&rcu_migrate_wq); | |
218 | } | |
219 | ||
2e597558 PM |
220 | extern int rcu_cpu_notify(struct notifier_block *self, |
221 | unsigned long action, void *hcpu); | |
222 | ||
f69b17d7 LJ |
223 | static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self, |
224 | unsigned long action, void *hcpu) | |
225 | { | |
2e597558 | 226 | rcu_cpu_notify(self, action, hcpu); |
f69b17d7 LJ |
227 | if (action == CPU_DYING) { |
228 | /* | |
229 | * preempt_disable() in on_each_cpu() prevents stop_machine(), | |
230 | * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);" | |
231 | * returns, all online cpus have queued rcu_barrier_func(), | |
232 | * and the dead cpu(if it exist) queues rcu_migrate_callback()s. | |
233 | * | |
234 | * These callbacks ensure _rcu_barrier() waits for all | |
235 | * RCU callbacks of the specified type to complete. | |
236 | */ | |
237 | atomic_set(&rcu_migrate_type_count, 3); | |
238 | call_rcu_bh(rcu_migrate_head, rcu_migrate_callback); | |
239 | call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback); | |
240 | call_rcu(rcu_migrate_head + 2, rcu_migrate_callback); | |
1423cc03 PM |
241 | } else if (action == CPU_DOWN_PREPARE) { |
242 | /* Don't need to wait until next removal operation. */ | |
f69b17d7 LJ |
243 | /* rcu_migrate_head is protected by cpu_add_remove_lock */ |
244 | wait_migrated_callbacks(); | |
245 | } | |
246 | ||
247 | return NOTIFY_OK; | |
248 | } | |
249 | ||
1da177e4 LT |
250 | void __init rcu_init(void) |
251 | { | |
2e597558 PM |
252 | int i; |
253 | ||
01c1c660 | 254 | __rcu_init(); |
2e597558 PM |
255 | cpu_notifier(rcu_barrier_cpu_hotplug, 0); |
256 | ||
257 | /* | |
258 | * We don't need protection against CPU-hotplug here because | |
259 | * this is called early in boot, before either interrupts | |
260 | * or the scheduler are operational. | |
261 | */ | |
262 | for_each_online_cpu(i) | |
263 | rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i); | |
1da177e4 LT |
264 | } |
265 | ||
a6826048 PM |
266 | void rcu_scheduler_starting(void) |
267 | { | |
268 | WARN_ON(num_online_cpus() != 1); | |
269 | WARN_ON(nr_context_switches() > 0); | |
270 | rcu_scheduler_active = 1; | |
271 | } |