TIME_WAIT状态下对接收到的数据包如何处理

int tcp_v4_rcv(struct sk_buff *skb)
{
	......

	sk = __inet_lookup_skb(&tcp_hashinfo, skb, th->source, th->dest);
	if (!sk)
		goto no_tcp_socket;
process:
	if (sk->sk_state == TCP_TIME_WAIT)
		goto do_time_wait;   
		......

discard_it:
	/* Discard frame. */
	kfree_skb(skb);
	return 0;
	......
do_time_wait:
	......

switch (tcp_timewait_state_process(inet_twsk(sk), skb, th)) {
	case TCP_TW_SYN: {
		struct sock *sk2 = inet_lookup_listener(dev_net(skb->dev),
							&tcp_hashinfo,
							iph->daddr, th->dest,
							inet_iif(skb));
		if (sk2) {
			inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
			inet_twsk_put(inet_twsk(sk));
			sk = sk2;
			goto process;
		}
		/* Fall through to ACK */
	}
	case TCP_TW_ACK:
		tcp_v4_timewait_ack(sk, skb);
		break;
	case TCP_TW_RST:
		goto no_tcp_socket;
	case TCP_TW_SUCCESS:;
	}
	goto discard_it;
}

if (tw->tw_substate == TCP_FIN_WAIT2) {
	/* Just repeat all the checks of tcp_rcv_state_process() */

	/* Out of window, send ACK */
	if (paws_reject ||
		!tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
			  tcptw->tw_rcv_nxt,
			  tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
		return TCP_TW_ACK;

	if (th->rst)
		goto kill;

	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
		goto kill_with_rst;

	/* Dup ACK? */
	if (!th->ack ||
		!after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
		TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
		inet_twsk_put(tw);
		return TCP_TW_SUCCESS;
	}

	/* New data or FIN. If new data arrive after half-duplex close,
	 * reset.
	 */
	if (!th->fin ||
		TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
kill_with_rst:
		inet_twsk_deschedule(tw, &tcp_death_row);
		inet_twsk_put(tw);
		return TCP_TW_RST;
	}

	/* FIN arrived, enter true time-wait state. */
	tw->tw_substate      = TCP_TIME_WAIT;
	tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
	if (tmp_opt.saw_tstamp) {
		tcptw->tw_ts_recent_stamp = get_seconds();
		tcptw->tw_ts_recent      = tmp_opt.rcv_tsval;
	}

	/* I am shamed, but failed to make it more elegant.
	 * Yes, it is direct reference to IP, which is impossible
	 * to generalize to IPv6. Taking into account that IPv6
	 * do not understand recycling in any case, it not
	 * a big problem in practice. --ANK 
	 */
	if (tw->tw_family == AF_INET &&
		tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp &&
		tcp_v4_tw_remember_stamp(tw))
		inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
				  TCP_TIMEWAIT_LEN);
	else
		inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
				  TCP_TIMEWAIT_LEN);

	return TCP_TW_ACK;
}

if (!paws_reject &&
	(TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
	(TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
	/* In window segment, it may be only reset or bare ack. */
	if (th->rst) {
		/* This is TIME_WAIT assassination, in two flavors.
		* Oh well... nobody has a sufficient solution to this
		* protocol bug yet.
		*/
		if (sysctl_tcp_rfc1337 == 0) {
kill:
			inet_twsk_deschedule(tw, &tcp_death_row);
			inet_twsk_put(tw);
			return TCP_TW_SUCCESS;
		}
	}
	inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
			  TCP_TIMEWAIT_LEN);

	if (tmp_opt.saw_tstamp) {
		tcptw->tw_ts_recent      = tmp_opt.rcv_tsval;
		tcptw->tw_ts_recent_stamp = get_seconds();
	}

	inet_twsk_put(tw);
	return TCP_TW_SUCCESS;
}

if (th->syn && !th->rst && !th->ack && !paws_reject &&
	(after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
	(tmp_opt.saw_tstamp &&
	  (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
	u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
	if (isn == 0)
		isn++;
	TCP_SKB_CB(skb)->when = isn;
	return TCP_TW_SYN;
}

if (!th->rst) {
	/* In this case we must reset the TIMEWAIT timer.
	 *
	 * If it is ACKless SYN it may be both old duplicate
	 * and new good SYN with random sequence number <rcv_nxt.
	 * Do not reschedule in the last case.
	 */
	if (paws_reject || th->ack)
		inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
				  TCP_TIMEWAIT_LEN);

	/* Send ACK. Note, we do not put the bucket,
	 * it will be released by caller.
	 */
	return TCP_TW_ACK;
}
inet_twsk_put(tw);
return TCP_TW_SUCCESS;

int __inet_hash_connect(struct inet_timewait_death_row *death_row,
		struct sock *sk, u32 port_offset,
		int (*check_established)(struct inet_timewait_death_row *,
			struct sock *, __u16, struct inet_timewait_sock **),
		void (*hash)(struct sock *sk))
{
	struct inet_hashinfo *hinfo = death_row->hashinfo;
	const unsigned short snum = inet_sk(sk)->num;
	struct inet_bind_hashbucket *head;
	struct inet_bind_bucket *tb;
	int ret;
	struct net *net = sock_net(sk);

	if (!snum) {
		......
	}

	head = &hinfo->bhash[inet_bhashfn(net, snum, hinfo->bhash_size)];
	tb  = inet_csk(sk)->icsk_bind_hash;
	spin_lock_bh(&head->lock);
	if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
		hash(sk);
		spin_unlock_bh(&head->lock);
		return 0;
	} else {
		spin_unlock(&head->lock);
		/* No definite answer... Walk to established hash table */
		ret = check_established(death_row, sk, snum, NULL);
out:
		local_bh_enable();
		return ret;
	}
}

/* called with local bh disabled */
static int __inet_check_established(struct inet_timewait_death_row *death_row,
					struct sock *sk, __u16 lport,
					struct inet_timewait_sock **twp)
{
	struct inet_hashinfo *hinfo = death_row->hashinfo;
	struct inet_sock *inet = inet_sk(sk);
	__be32 daddr = inet->rcv_saddr;
	__be32 saddr = inet->daddr;
	int dif = sk->sk_bound_dev_if;
	INET_ADDR_COOKIE(acookie, saddr, daddr)
	const __portpair ports = INET_COMBINED_PORTS(inet->dport, lport);
	struct net *net = sock_net(sk);
	unsigned int hash = inet_ehashfn(net, daddr, lport, saddr, inet->dport);
	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
	spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
	struct sock *sk2;
	const struct hlist_nulls_node *node;
	struct inet_timewait_sock *tw;

	spin_lock(lock);

	/* Check TIME-WAIT sockets first. */
	sk_nulls_for_each(sk2, node, &head->twchain) {
		tw = inet_twsk(sk2);

	if (INET_TW_MATCH(sk2, net, hash, acookie,
					saddr, daddr, ports, dif)) {
			if (twsk_unique(sk, sk2, twp))
				goto unique;
			else
				goto not_unique;
		}
	}
	tw = NULL;

	/* And established part... */
	sk_nulls_for_each(sk2, node, &head->chain) {
		if (INET_MATCH(sk2, net, hash, acookie,
					saddr, daddr, ports, dif))
			goto not_unique;
	}

unique:
	......
	return 0;

not_unique:
	spin_unlock(lock);
	return -EADDRNOTAVAIL;
}

int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
{
	const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
	struct tcp_sock *tp = tcp_sk(sk);

	if (tcptw->tw_ts_recent_stamp &&
		(twp == NULL || (sysctl_tcp_tw_reuse &&
				get_seconds() - tcptw->tw_ts_recent_stamp > 1))) {
		......
		return 1;
	}

	return 0;
}