Zone expiration aborts transaction in progress

Fixes #929 (closed)

src/knot/events/handlers/expire.c

-/*  Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+/*  Copyright (C) 2024 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -32,6 +32,11 @@ int event_expire(conf_t *conf, zone_t *zone)
 	log_zone_info(zone->name, "zone expired");
 
 	synchronize_rcu();
+
+	pthread_mutex_lock(&zone->cu_lock);
+	zone_control_clear(zone);
+	pthread_mutex_unlock(&zone->cu_lock);
+
 	knot_sem_wait(&zone->cow_lock);
 	zone_contents_deep_free(expired);
 	knot_sem_post(&zone->cow_lock);