diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 1c59ec161cf8..ce203154d8ce 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -152,6 +152,10 @@ static void default_idle(void)
 	local_mcck_disable();
 	if (test_thread_flag(TIF_MCCK_PENDING)) {
 		local_mcck_enable();
+		/* disable monitor call class 0 */
+		__ctl_clear_bit(8, 15);
+		atomic_notifier_call_chain(&idle_chain, S390_CPU_NOT_IDLE,
+					   hcpu);
 		local_irq_enable();
 		s390_handle_mcck();
 		return;
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 76a5dd1b4ce9..cb232c155360 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -209,8 +209,6 @@ static void stop_hz_timer(void)
  */
 static void start_hz_timer(void)
 {
-	BUG_ON(!in_interrupt());
-
 	if (!cpu_isset(smp_processor_id(), nohz_cpu_mask))
 		return;
 	account_ticks(get_clock());