Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6

[linux-2.6] / kernel / rcupdate.c

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 0ccd0095ebdc574693556388b8e38edc622eb2a3..760dfc233a00ae103fdce2bfe335ad9b14ca39cc 100644 (file)
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -115,7 +115,17 @@ void rcu_barrier(void)
        mutex_lock(&rcu_barrier_mutex);
        init_completion(&rcu_barrier_completion);
        atomic_set(&rcu_barrier_cpu_count, 0);
+       /*
+        * The queueing of callbacks in all CPUs must be atomic with
+        * respect to RCU, otherwise one CPU may queue a callback,
+        * wait for a grace period, decrement barrier count and call
+        * complete(), while other CPUs have not yet queued anything.
+        * So, we need to make sure that grace periods cannot complete
+        * until all the callbacks are queued.
+        */
+       rcu_read_lock();
        on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+       rcu_read_unlock();
        wait_for_completion(&rcu_barrier_completion);
        mutex_unlock(&rcu_barrier_mutex);
 }