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 *
18 * Copyright IBM Corporation, 2001
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>
42 #include <linux/percpu.h>
43 #include <linux/notifier.h>
44 #include <linux/cpu.h>
45 #include <linux/mutex.h>
46 #include <linux/module.h>
47 #include <linux/kernel_stat.h>
48
49 enum rcu_barrier {
50 RCU_BARRIER_STD,
51 RCU_BARRIER_BH,
52 RCU_BARRIER_SCHED,
53 };
54
55 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
56 static atomic_t rcu_barrier_cpu_count;
57 static DEFINE_MUTEX(rcu_barrier_mutex);
58 static struct completion rcu_barrier_completion;
59 int rcu_scheduler_active __read_mostly;
60
61 /*
62 * Awaken the corresponding synchronize_rcu() instance now that a
63 * grace period has elapsed.
64 */
wakeme_after_rcu(struct rcu_head * head)65 void wakeme_after_rcu(struct rcu_head *head)
66 {
67 struct rcu_synchronize *rcu;
68
69 rcu = container_of(head, struct rcu_synchronize, head);
70 complete(&rcu->completion);
71 }
72
73 /**
74 * synchronize_rcu - wait until a grace period has elapsed.
75 *
76 * Control will return to the caller some time after a full grace
77 * period has elapsed, in other words after all currently executing RCU
78 * read-side critical sections have completed. RCU read-side critical
79 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
80 * and may be nested.
81 */
synchronize_rcu(void)82 void synchronize_rcu(void)
83 {
84 struct rcu_synchronize rcu;
85
86 if (rcu_blocking_is_gp())
87 return;
88
89 init_completion(&rcu.completion);
90 /* Will wake me after RCU finished. */
91 call_rcu(&rcu.head, wakeme_after_rcu);
92 /* Wait for it. */
93 wait_for_completion(&rcu.completion);
94 }
95 EXPORT_SYMBOL_GPL(synchronize_rcu);
96
rcu_barrier_callback(struct rcu_head * notused)97 static void rcu_barrier_callback(struct rcu_head *notused)
98 {
99 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
100 complete(&rcu_barrier_completion);
101 }
102
103 /*
104 * Called with preemption disabled, and from cross-cpu IRQ context.
105 */
rcu_barrier_func(void * type)106 static void rcu_barrier_func(void *type)
107 {
108 int cpu = smp_processor_id();
109 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
110
111 atomic_inc(&rcu_barrier_cpu_count);
112 switch ((enum rcu_barrier)type) {
113 case RCU_BARRIER_STD:
114 call_rcu(head, rcu_barrier_callback);
115 break;
116 case RCU_BARRIER_BH:
117 call_rcu_bh(head, rcu_barrier_callback);
118 break;
119 case RCU_BARRIER_SCHED:
120 call_rcu_sched(head, rcu_barrier_callback);
121 break;
122 }
123 }
124
125 /*
126 * Orchestrate the specified type of RCU barrier, waiting for all
127 * RCU callbacks of the specified type to complete.
128 */
_rcu_barrier(enum rcu_barrier type)129 static void _rcu_barrier(enum rcu_barrier type)
130 {
131 BUG_ON(in_interrupt());
132 /* Take cpucontrol mutex to protect against CPU hotplug */
133 mutex_lock(&rcu_barrier_mutex);
134 init_completion(&rcu_barrier_completion);
135 /*
136 * Initialize rcu_barrier_cpu_count to 1, then invoke
137 * rcu_barrier_func() on each CPU, so that each CPU also has
138 * incremented rcu_barrier_cpu_count. Only then is it safe to
139 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
140 * might complete its grace period before all of the other CPUs
141 * did their increment, causing this function to return too
142 * early.
143 */
144 atomic_set(&rcu_barrier_cpu_count, 1);
145 on_each_cpu(rcu_barrier_func, (void *)type, 1);
146 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
147 complete(&rcu_barrier_completion);
148 wait_for_completion(&rcu_barrier_completion);
149 mutex_unlock(&rcu_barrier_mutex);
150 }
151
152 /**
153 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
154 */
rcu_barrier(void)155 void rcu_barrier(void)
156 {
157 _rcu_barrier(RCU_BARRIER_STD);
158 }
159 EXPORT_SYMBOL_GPL(rcu_barrier);
160
161 /**
162 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
163 */
rcu_barrier_bh(void)164 void rcu_barrier_bh(void)
165 {
166 _rcu_barrier(RCU_BARRIER_BH);
167 }
168 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
169
170 /**
171 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
172 */
rcu_barrier_sched(void)173 void rcu_barrier_sched(void)
174 {
175 _rcu_barrier(RCU_BARRIER_SCHED);
176 }
177 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
178
rcu_init(void)179 void __init rcu_init(void)
180 {
181 __rcu_init();
182 }
183
rcu_scheduler_starting(void)184 void rcu_scheduler_starting(void)
185 {
186 WARN_ON(num_online_cpus() != 1);
187 WARN_ON(nr_context_switches() > 0);
188 rcu_scheduler_active = 1;
189 }
190