fix: prevent coredump in zone-reload by introducing semaphore protect…

…ion...

when generating new zone_contents_t for newzone

fixes #939

src/knot/zone/zonedb-load.c

@@ -652,6 +652,7 @@ int zone_reload_modules(conf_t *conf, server_t *server, const knot_dname_t *zone
  if (newzone == NULL) {
  return KNOT_ENOMEM;
  }
+ knot_sem_wait(&newzone->cow_lock);
  conf_activate_modules(conf, server, newzone->name, &newzone->query_modules,
  &newzone->query_plan);
 
@@ -663,6 +664,7 @@ int zone_reload_modules(conf_t *conf, server_t *server, const knot_dname_t *zone
  assert(newzone->contents == oldzone->contents);
  oldzone->contents = NULL; // contents have been re-used by newzone
 
+ knot_sem_post(&newzone->cow_lock);
  knot_sem_post(&oldzone->cow_lock);
  zone_free(&oldzone);