NULLS_MARKER
((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
#define HLIST_NULLS_HEAD_INIT(nulls) {.first = (struct hlist_nulls_node *)NULLS_MARKER(nulls)}
WRITE_ONCE(n->next, (struct hlist_nulls_node *)NULLS_MARKER(NULL));
((void *)NULLS_MARKER(((unsigned long) (ptr)) >> 1))