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>
48 static DEFINE_PER_CPU(struct rcu_head
, rcu_barrier_head
) = {NULL
};
49 static atomic_t rcu_barrier_cpu_count
;
50 static DEFINE_MUTEX(rcu_barrier_mutex
);
51 static struct completion rcu_barrier_completion
;
54 * Awaken the corresponding synchronize_rcu() instance now that a
55 * grace period has elapsed.
57 void wakeme_after_rcu(struct rcu_head
*head
)
59 struct rcu_synchronize
*rcu
;
61 rcu
= container_of(head
, struct rcu_synchronize
, head
);
62 complete(&rcu
->completion
);
66 * synchronize_rcu - wait until a grace period has elapsed.
68 * Control will return to the caller some time after a full grace
69 * period has elapsed, in other words after all currently executing RCU
70 * read-side critical sections have completed. RCU read-side critical
71 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
74 synchronize_rcu_xxx(synchronize_rcu
, call_rcu
)
75 EXPORT_SYMBOL_GPL(synchronize_rcu
);
77 static void rcu_barrier_callback(struct rcu_head
*notused
)
79 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
80 complete(&rcu_barrier_completion
);
84 * Called with preemption disabled, and from cross-cpu IRQ context.
86 static void rcu_barrier_func(void *notused
)
88 int cpu
= smp_processor_id();
89 struct rcu_head
*head
= &per_cpu(rcu_barrier_head
, cpu
);
91 atomic_inc(&rcu_barrier_cpu_count
);
92 call_rcu(head
, rcu_barrier_callback
);
96 * rcu_barrier - Wait until all the in-flight RCUs are complete.
98 void rcu_barrier(void)
100 BUG_ON(in_interrupt());
101 /* Take cpucontrol mutex to protect against CPU hotplug */
102 mutex_lock(&rcu_barrier_mutex
);
103 init_completion(&rcu_barrier_completion
);
104 atomic_set(&rcu_barrier_cpu_count
, 0);
106 * The queueing of callbacks in all CPUs must be atomic with
107 * respect to RCU, otherwise one CPU may queue a callback,
108 * wait for a grace period, decrement barrier count and call
109 * complete(), while other CPUs have not yet queued anything.
110 * So, we need to make sure that grace periods cannot complete
111 * until all the callbacks are queued.
114 on_each_cpu(rcu_barrier_func
, NULL
, 0, 1);
116 wait_for_completion(&rcu_barrier_completion
);
117 mutex_unlock(&rcu_barrier_mutex
);
119 EXPORT_SYMBOL_GPL(rcu_barrier
);
121 void __init
rcu_init(void)