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Commit 55e84dd7 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'tcp-revert-a-F-RTO-extension-due-to-broken-middle-boxes' 

Yuchung Cheng says:

====================
tcp: revert a F-RTO extension due to broken middle-boxes

This patch series reverts a (non-standard) TCP F-RTO extension that aimed
to detect more spurious timeouts. Unfortunately it could result in poor
performance due to broken middle-boxes that modify TCP packets. E.g.
https://www.spinics.net/lists/netdev/msg484154.html


We believe the best and simplest solution is to just revert the change.
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents c8431622 fc68e171

net/ipv4/tcp_input.c

+7 −16
Original line number Diff line number Diff line
@@ -1971,11 +1971,6 @@ void tcp_enter_loss(struct sock *sk) 
	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous

	 * loss recovery is underway except recurring timeout(s) on

	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing

	 *

	 * In theory F-RTO can be used repeatedly during loss recovery.

	 * In practice this interacts badly with broken middle-boxes that

	 * falsely raise the receive window, which results in repeated

	 * timeouts and stop-and-go behavior.

	 */

	tp->frto = net->ipv4.sysctl_tcp_frto &&

		   (new_recovery || icsk->icsk_retransmits) &&
@@ -2631,18 +2626,14 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack, 
	    tcp_try_undo_loss(sk, false))

		return;



	/* The ACK (s)acks some never-retransmitted data meaning not all

	 * the data packets before the timeout were lost. Therefore we

	 * undo the congestion window and state. This is essentially

	 * the operation in F-RTO (RFC5682 section 3.1 step 3.b). Since

	 * a retransmitted skb is permantly marked, we can apply such an

	 * operation even if F-RTO was not used.

	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */

		/* Step 3.b. A timeout is spurious if not all data are

		 * lost, i.e., never-retransmitted data are (s)acked.

		 */

		if ((flag & FLAG_ORIG_SACK_ACKED) &&

	    tcp_try_undo_loss(sk, tp->undo_marker))

		    tcp_try_undo_loss(sk, true))

			return;



	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */

		if (after(tp->snd_nxt, tp->high_seq)) {

			if (flag & FLAG_DATA_SACKED || is_dupack)

				tp->frto = 0; /* Step 3.a. loss was real */