1 files changed, 10 insertions, 9 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 467d5940f624..ad63af8b2521 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -119,18 +119,19 @@ static void _rcu_barrier(enum rcu_barrier type)
         /* Take cpucontrol mutex to protect against CPU hotplug */
         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.
+         * Initialize rcu_barrier_cpu_count to 1, then invoke
+         * rcu_barrier_func() on each CPU, so that each CPU also has
+         * incremented rcu_barrier_cpu_count.  Only then is it safe to
+         * decrement rcu_barrier_cpu_count -- otherwise the first CPU
+         * might complete its grace period before all of the other CPUs
+         * did their increment, causing this function to return too
+         * early.
          */
-        rcu_read_lock();
+        atomic_set(&rcu_barrier_cpu_count, 1);
         on_each_cpu(rcu_barrier_func, (void *)type, 1);
-        rcu_read_unlock();
+        if (atomic_dec_and_test(&rcu_barrier_cpu_count))
+                complete(&rcu_barrier_completion);
         wait_for_completion(&rcu_barrier_completion);
         mutex_unlock(&rcu_barrier_mutex);
 }