static void sctp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
	struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
	struct sctp_ep_common *rcvr = chunk->rcvr;

	/* Hold the assoc/ep while hanging on the backlog queue.
	 * This way, we know structures we need will not disappear from us
	 */
	if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
		sctp_association_hold(sctp_assoc(rcvr));
	else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
		sctp_endpoint_hold(sctp_ep(rcvr));
	else
		BUG();

	sk_add_backlog(sk, skb);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.