rcu: Kick rcuo kthreads after their CPU goes offline

If a no-CBs CPU were to post an RCU callback with interrupts disabled
after it entered the idle loop for the last time, there might be no
deferred wakeup for the corresponding rcuo kthreads.  This commit
therefore adds a set of calls to do_nocb_deferred_wakeup() after the
CPU has gone completely offline.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -3497,8 +3497,10 @@ static int rcu_cpu_notify(struct notifier_block *self,
 	case CPU_DEAD_FROZEN:
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN:
-		for_each_rcu_flavor(rsp)
+		for_each_rcu_flavor(rsp) {
 			rcu_cleanup_dead_cpu(cpu, rsp);
+			do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
+		}
 		break;
 	default:
 		break;