2 * Read-Copy Update mechanism for mutual exclusion
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.
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.
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.
18 * Copyright IBM Corporation, 2001
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
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>
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;
60 * Awaken the corresponding synchronize_rcu() instance now that a
61 * grace period has elapsed.
63 void wakeme_after_rcu(struct rcu_head *head)
65 struct rcu_synchronize *rcu;
67 rcu = container_of(head, struct rcu_synchronize, head);
68 complete(&rcu->completion);
72 * synchronize_rcu - wait until a grace period has elapsed.
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(),
80 void synchronize_rcu(void); /* Makes kernel-doc tools happy */
81 synchronize_rcu_xxx(synchronize_rcu, call_rcu)
82 EXPORT_SYMBOL_GPL(synchronize_rcu);
84 static void rcu_barrier_callback(struct rcu_head *notused)
86 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
87 complete(&rcu_barrier_completion);
91 * Called with preemption disabled, and from cross-cpu IRQ context.
93 static void rcu_barrier_func(void *type)
95 int cpu = smp_processor_id();
96 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
98 atomic_inc(&rcu_barrier_cpu_count);
99 switch ((enum rcu_barrier)type) {
100 case RCU_BARRIER_STD:
101 call_rcu(head, rcu_barrier_callback);
104 call_rcu_bh(head, rcu_barrier_callback);
106 case RCU_BARRIER_SCHED:
107 call_rcu_sched(head, rcu_barrier_callback);
113 * Orchestrate the specified type of RCU barrier, waiting for all
114 * RCU callbacks of the specified type to complete.
116 static void _rcu_barrier(enum rcu_barrier type)
118 BUG_ON(in_interrupt());
119 /* Take cpucontrol mutex to protect against CPU hotplug */
120 mutex_lock(&rcu_barrier_mutex);
121 init_completion(&rcu_barrier_completion);
123 * Initialize rcu_barrier_cpu_count to 1, then invoke
124 * rcu_barrier_func() on each CPU, so that each CPU also has
125 * incremented rcu_barrier_cpu_count. Only then is it safe to
126 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
127 * might complete its grace period before all of the other CPUs
128 * did their increment, causing this function to return too
131 atomic_set(&rcu_barrier_cpu_count, 1);
132 on_each_cpu(rcu_barrier_func, (void *)type, 1);
133 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
134 complete(&rcu_barrier_completion);
135 wait_for_completion(&rcu_barrier_completion);
136 mutex_unlock(&rcu_barrier_mutex);
140 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
142 void rcu_barrier(void)
144 _rcu_barrier(RCU_BARRIER_STD);
146 EXPORT_SYMBOL_GPL(rcu_barrier);
149 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
151 void rcu_barrier_bh(void)
153 _rcu_barrier(RCU_BARRIER_BH);
155 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
158 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
160 void rcu_barrier_sched(void)
162 _rcu_barrier(RCU_BARRIER_SCHED);
164 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
166 void __init rcu_init(void)