-It -is- safe for synchronize_sched() and synchronize_rcu_bh() to return
-immediately on an UP system. It is also safe for synchronize_rcu()
-to return immediately on UP systems, except when running preemptable
-RCU.
+Note that it -is- safe for synchronize_rcu() to return immediately on
+UP systems, including !PREEMPT SMP builds running on UP systems.