diff --git a/[refs] b/[refs]
index 881dee34c0b5..4836ca24edf9 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4d576b57b50a92801e6493e76e5243d6cff193d2
+refs/heads/master: 2496afbf1e50c70f80992656bcb730c8583ddac3
diff --git a/trunk/arch/x86/xen/spinlock.c b/trunk/arch/x86/xen/spinlock.c
index 2f91e5651926..36a5141108df 100644
--- a/trunk/arch/x86/xen/spinlock.c
+++ b/trunk/arch/x86/xen/spinlock.c
@@ -326,8 +326,13 @@ static void xen_spin_unlock(struct raw_spinlock *lock)
 	smp_wmb();		/* make sure no writes get moved after unlock */
 	xl->lock = 0;		/* release lock */
 
-	/* make sure unlock happens before kick */
-	barrier();
+	/*
+	 * Make sure unlock happens before checking for waiting
+	 * spinners.  We need a strong barrier to enforce the
+	 * write-read ordering to different memory locations, as the
+	 * CPU makes no implied guarantees about their ordering.
+	 */
+	mb();
 
 	if (unlikely(xl->spinners))
 		xen_spin_unlock_slow(xl);