scftorture: Wait until scf_cleanup_handler() completes.

The smp_call_function() needs to be invoked with the wait flag set to
wait until scf_cleanup_handler() is done. This ensures that all SMP
function calls, that have been queued earlier, complete at this point.

Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: Sebastian Andrzej Siewior

kernel/scftorture.c

@@ -523,7 +523,7 @@ static void scf_torture_cleanup(void)
 			torture_stop_kthread("scftorture_invoker", scf_stats_p[i].task);
 	else
 		goto end;
-	smp_call_function(scf_cleanup_handler, NULL, 0);
+	smp_call_function(scf_cleanup_handler, NULL, 1);
 	torture_stop_kthread(scf_torture_stats, scf_torture_stats_task);
 	scf_torture_stats_print();  // -After- the stats thread is stopped!
 	kfree(scf_stats_p);  // -After- the last stats print has completed!