MERGE-master-patchset-edits
[linux-2.6/openmoko-kernel.git] / kernel / rcupdate.c
blobd92a76a881aa47a9aa059c3221910834f6c50cf8
1 /*
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.
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)
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>
48 enum rcu_barrier {
49 RCU_BARRIER_STD,
50 RCU_BARRIER_BH,
51 RCU_BARRIER_SCHED,
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);
71 /**
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(),
78 * and may be nested.
80 void synchronize_rcu(void)
82 struct rcu_synchronize rcu;
83 init_completion(&rcu.completion);
84 /* Will wake me after RCU finished. */
85 call_rcu(&rcu.head, wakeme_after_rcu);
86 /* Wait for it. */
87 wait_for_completion(&rcu.completion);
89 EXPORT_SYMBOL_GPL(synchronize_rcu);
91 static void rcu_barrier_callback(struct rcu_head *notused)
93 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
94 complete(&rcu_barrier_completion);
98 * Called with preemption disabled, and from cross-cpu IRQ context.
100 static void rcu_barrier_func(void *type)
102 int cpu = smp_processor_id();
103 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
105 atomic_inc(&rcu_barrier_cpu_count);
106 switch ((enum rcu_barrier)type) {
107 case RCU_BARRIER_STD:
108 call_rcu(head, rcu_barrier_callback);
109 break;
110 case RCU_BARRIER_BH:
111 call_rcu_bh(head, rcu_barrier_callback);
112 break;
113 case RCU_BARRIER_SCHED:
114 call_rcu_sched(head, rcu_barrier_callback);
115 break;
120 * Orchestrate the specified type of RCU barrier, waiting for all
121 * RCU callbacks of the specified type to complete.
123 static void _rcu_barrier(enum rcu_barrier type)
125 BUG_ON(in_interrupt());
126 /* Take cpucontrol mutex to protect against CPU hotplug */
127 mutex_lock(&rcu_barrier_mutex);
128 init_completion(&rcu_barrier_completion);
130 * Initialize rcu_barrier_cpu_count to 1, then invoke
131 * rcu_barrier_func() on each CPU, so that each CPU also has
132 * incremented rcu_barrier_cpu_count. Only then is it safe to
133 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
134 * might complete its grace period before all of the other CPUs
135 * did their increment, causing this function to return too
136 * early.
138 atomic_set(&rcu_barrier_cpu_count, 1);
139 on_each_cpu(rcu_barrier_func, (void *)type, 1);
140 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
141 complete(&rcu_barrier_completion);
142 wait_for_completion(&rcu_barrier_completion);
143 mutex_unlock(&rcu_barrier_mutex);
147 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
149 void rcu_barrier(void)
151 _rcu_barrier(RCU_BARRIER_STD);
153 EXPORT_SYMBOL_GPL(rcu_barrier);
156 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
158 void rcu_barrier_bh(void)
160 _rcu_barrier(RCU_BARRIER_BH);
162 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
165 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
167 void rcu_barrier_sched(void)
169 _rcu_barrier(RCU_BARRIER_SCHED);
171 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
173 void __init rcu_init(void)
175 __rcu_init();