diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index e486f7c..3731141 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -907,6 +907,12 @@
 	unsigned long gp_duration;
 
 	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
+
+	/*
+	 * Ensure that all grace-period and pre-grace-period activity
+	 * is seen before the assignment to rsp->completed.
+	 */
+	smp_mb(); /* See above block comment. */
 	gp_duration = jiffies - rsp->gp_start;
 	if (gp_duration > rsp->gp_max)
 		rsp->gp_max = gp_duration;