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Commit f1ecd5d9 authored by Damian Lukowski's avatar Damian Lukowski Committed by David S. Miller
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Revert Backoff [v3]: Revert RTO on ICMP destination unreachable 



Here, an ICMP host/network unreachable message, whose payload fits to
TCP's SND.UNA, is taken as an indication that the RTO retransmission has
not been lost due to congestion, but because of a route failure
somewhere along the path.
With true congestion, a router won't trigger such a message and the
patched TCP will operate as standard TCP.

This patch reverts one RTO backoff, if an ICMP host/network unreachable
message, whose payload fits to TCP's SND.UNA, arrives.
Based on the new RTO, the retransmission timer is reset to reflect the
remaining time, or - if the revert clocked out the timer - a retransmission
is sent out immediately.
Backoffs are only reverted, if TCP is in RTO loss recovery, i.e. if
there have been retransmissions and reversible backoffs, already.

Changes from v2:
1) Renaming of skb in tcp_v4_err() moved to another patch.
2) Reintroduced tcp_bound_rto() and __tcp_set_rto().
3) Fixed code comments.

Signed-off-by: default avatarDamian Lukowski <damian@tvk.rwth-aachen.de>
Acked-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4d1a2d9e

include/net/tcp.h

+12 −0
Original line number Diff line number Diff line
@@ -469,6 +469,7 @@ extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, 
				      int nonagle);

extern int tcp_may_send_now(struct sock *sk);

extern int tcp_retransmit_skb(struct sock *, struct sk_buff *);

extern void tcp_retransmit_timer(struct sock *sk);

extern void tcp_xmit_retransmit_queue(struct sock *);

extern void tcp_simple_retransmit(struct sock *);

extern int tcp_trim_head(struct sock *, struct sk_buff *, u32);
@@ -521,6 +522,17 @@ extern int tcp_mtu_to_mss(struct sock *sk, int pmtu); 
extern int tcp_mss_to_mtu(struct sock *sk, int mss);

extern void tcp_mtup_init(struct sock *sk);



static inline void tcp_bound_rto(const struct sock *sk)

{

	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)

		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;

}



static inline u32 __tcp_set_rto(const struct tcp_sock *tp)

{

	return (tp->srtt >> 3) + tp->rttvar;

}



static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)

{

	tp->pred_flags = htonl((tp->tcp_header_len << 26) |

net/ipv4/tcp_input.c

+2 −3
Original line number Diff line number Diff line
@@ -685,7 +685,7 @@ static inline void tcp_set_rto(struct sock *sk) 
	 *    is invisible. Actually, Linux-2.4 also generates erratic

	 *    ACKs in some circumstances.

	 */

	inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;

	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);



	/* 2. Fixups made earlier cannot be right.

	 *    If we do not estimate RTO correctly without them,
@@ -696,8 +696,7 @@ static inline void tcp_set_rto(struct sock *sk) 
	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo

	 * guarantees that rto is higher.

	 */

	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)

		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;

	tcp_bound_rto(sk);

}



/* Save metrics learned by this TCP session.

net/ipv4/tcp_ipv4.c

+37 −0
Original line number Diff line number Diff line
@@ -332,12 +332,15 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) 
{

	struct iphdr *iph = (struct iphdr *)icmp_skb->data;

	struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2));

	struct inet_connection_sock *icsk;

	struct tcp_sock *tp;

	struct inet_sock *inet;

	const int type = icmp_hdr(icmp_skb)->type;

	const int code = icmp_hdr(icmp_skb)->code;

	struct sock *sk;

	struct sk_buff *skb;

	__u32 seq;

	__u32 remaining;

	int err;

	struct net *net = dev_net(icmp_skb->dev);
@@ -367,6 +370,7 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) 
	if (sk->sk_state == TCP_CLOSE)

		goto out;



	icsk = inet_csk(sk);

	tp = tcp_sk(sk);

	seq = ntohl(th->seq);

	if (sk->sk_state != TCP_LISTEN &&
@@ -393,6 +397,39 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) 
		}



		err = icmp_err_convert[code].errno;

		/* check if icmp_skb allows revert of backoff

		 * (see draft-zimmermann-tcp-lcd) */

		if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH)

			break;

		if (seq != tp->snd_una  || !icsk->icsk_retransmits ||

		    !icsk->icsk_backoff)

			break;



		icsk->icsk_backoff--;

		inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) <<

					 icsk->icsk_backoff;

		tcp_bound_rto(sk);



		skb = tcp_write_queue_head(sk);

		BUG_ON(!skb);



		remaining = icsk->icsk_rto - min(icsk->icsk_rto,

				tcp_time_stamp - TCP_SKB_CB(skb)->when);



		if (remaining) {

			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,

						  remaining, TCP_RTO_MAX);

		} else if (sock_owned_by_user(sk)) {

			/* RTO revert clocked out retransmission,

			 * but socket is locked. Will defer. */

			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,

						  HZ/20, TCP_RTO_MAX);

		} else {

			/* RTO revert clocked out retransmission.

			 * Will retransmit now */

			tcp_retransmit_timer(sk);

		}



		break;

	case ICMP_TIME_EXCEEDED:

		err = EHOSTUNREACH;

net/ipv4/tcp_timer.c

+1 −1
Original line number Diff line number Diff line
@@ -279,7 +279,7 @@ static void tcp_probe_timer(struct sock *sk) 
 *	The TCP retransmit timer.

 */



static void tcp_retransmit_timer(struct sock *sk)

void tcp_retransmit_timer(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);