MDEV-17481 mariadb service won't shutdown when it's running and the OS datetime updated backwards

__pthread_cond_timedwait() in page cleaner hangs if os time moved
backwards.Workaround could be waking up the page cleaner thread in
logs_empty_and_mark_files_at_shutdown(). But there is possibility that
server could hang when server is running. So InnoDB should wake up page
cleaner thread periodically in srv_master_do_idle_tasks().

storage/innobase/log/log0log.cc

@@ -1936,6 +1936,9 @@ logs_empty_and_mark_files_at_shutdown(void)
 				"Waiting for page cleaner");
 			ib::info() << "Waiting for page_cleaner to "
 				"finish flushing of buffer pool";
+			/* This is a workaround to avoid the InnoDB hang
+			when OS datetime changed backwards */
+			os_event_set(buf_flush_event);
 			count = 0;
 		}
 	}

storage/innobase/srv/srv0srv.cc

@@ -2365,6 +2365,10 @@ srv_master_do_idle_tasks(void)
 	log_checkpoint(true);
 	MONITOR_INC_TIME_IN_MICRO_SECS(MONITOR_SRV_CHECKPOINT_MICROSECOND,
 				       counter_time);
+
+	/* This is a workaround to avoid the InnoDB hang when OS datetime
+	changed backwards.*/
+	os_event_set(buf_flush_event);
 }
 
 /** Perform shutdown tasks.