From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuchung Cheng Subject: [PATCH] tcp: undo spurious timeout after SACK reneging Date: Sun, 24 Mar 2013 13:42:25 -0700 Message-ID: <1364157745-24866-1-git-send-email-ycheng@google.com> Cc: netdev@vger.kernel.org, Yuchung Cheng To: davem@davemloft.net, ncardwell@google.com, edumazet@google.com, nanditad@google.com Return-path: Received: from mail-ve0-f201.google.com ([209.85.128.201]:46378 "EHLO mail-ve0-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753869Ab3CXUm2 (ORCPT ); Sun, 24 Mar 2013 16:42:28 -0400 Received: by mail-ve0-f201.google.com with SMTP id 14so560889vea.0 for ; Sun, 24 Mar 2013 13:42:27 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: On SACK reneging the sender immediately retransmits and forces a timeout but disables Eifel (undo). If the (buggy) receiver does not drop any packet this can trigger a false slow-start retransmit storm driven by the ACKs of the original packets. This can be detected with undo and TCP timestamps. Signed-off-by: Yuchung Cheng --- net/ipv4/tcp_input.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index b2b3619..6d9ca35 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1858,11 +1858,8 @@ void tcp_enter_loss(struct sock *sk, int how) if (tcp_is_reno(tp)) tcp_reset_reno_sack(tp); - if (!how) { - /* Push undo marker, if it was plain RTO and nothing - * was retransmitted. */ - tp->undo_marker = tp->snd_una; - } else { + tp->undo_marker = tp->snd_una; + if (how) { tp->sacked_out = 0; tp->fackets_out = 0; } -- 1.8.1.3