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/completion.h>
43 #include <linux/percpu.h>
44 #include <linux/notifier.h>
45 #include <linux/cpu.h>
46 #include <linux/mutex.h>
47 #include <linux/module.h>
48
49 struct rcu_synchronize {
50 struct rcu_head head;
51 struct completion completion;
52 };
53
54 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
55 static atomic_t rcu_barrier_cpu_count;
56 static DEFINE_MUTEX(rcu_barrier_mutex);
57 static struct completion rcu_barrier_completion;
58
59 /*
60 * Awaken the corresponding synchronize_rcu() instance now that a
61 * grace period has elapsed.
62 */
63 static void wakeme_after_rcu(struct rcu_head *head)
64 {
65 struct rcu_synchronize *rcu;
66
67 rcu = container_of(head, struct rcu_synchronize, head);
68 complete(&rcu->completion);
69 }
70
71 /**
72 * synchronize_rcu - wait until a grace period has elapsed.
73 *
74 * Control will return to the caller some time after a full grace
75 * period has elapsed, in other words after all currently executing RCU
76 * read-side critical sections have completed. RCU read-side critical
77 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
78 * and may be nested.
79 */
80 void synchronize_rcu(void)
81 {
82 struct rcu_synchronize rcu;
83
84 init_completion(&rcu.completion);
85 /* Will wake me after RCU finished */
86 call_rcu(&rcu.head, wakeme_after_rcu);
87
88 rcu_boost_readers();
89
90 /* Wait for it */
91 wait_for_completion(&rcu.completion);
92 rcu_unboost_readers();
93 }
94 EXPORT_SYMBOL_GPL(synchronize_rcu);
95
96 static void rcu_barrier_callback(struct rcu_head *notused)
97 {
98 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
99 complete(&rcu_barrier_completion);
100 }
101
102 /*
103 * Called with preemption disabled, and from cross-cpu IRQ context.
104 */
105 static void rcu_barrier_func(void *notused)
106 {
107 int cpu = smp_processor_id();
108 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
109
110 atomic_inc(&rcu_barrier_cpu_count);
111 call_rcu(head, rcu_barrier_callback);
112 }
113
114 /**
115 * rcu_barrier - Wait until all the in-flight RCUs are complete.
116 */
117 void rcu_barrier(void)
118 {
119 BUG_ON(in_interrupt());
120 /* Take cpucontrol mutex to protect against CPU hotplug */
121 mutex_lock(&rcu_barrier_mutex);
122 init_completion(&rcu_barrier_completion);
123 atomic_set(&rcu_barrier_cpu_count, 0);
124 /*
125 * The queueing of callbacks in all CPUs must be atomic with
126 * respect to RCU, otherwise one CPU may queue a callback,
127 * wait for a grace period, decrement barrier count and call
128 * complete(), while other CPUs have not yet queued anything.
129 * So, we need to make sure that grace periods cannot complete
130 * until all the callbacks are queued.
131 */
132 rcu_read_lock();
133 on_each_cpu(rcu_barrier_func, NULL, 0, 1);
134 rcu_read_unlock();
135 wait_for_completion(&rcu_barrier_completion);
136 mutex_unlock(&rcu_barrier_mutex);
137 }
138 EXPORT_SYMBOL_GPL(rcu_barrier);
139
140 void __init rcu_init(void)
141 {
142 __rcu_init();
143 }
144
145
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