Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753698AbaFWIs5 (ORCPT ); Mon, 23 Jun 2014 04:48:57 -0400 Received: from ip4-83-240-18-248.cust.nbox.cz ([83.240.18.248]:55559 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752589AbaFWIc3 (ORCPT ); Mon, 23 Jun 2014 04:32:29 -0400 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Yuchung Cheng , Neal Cardwell , "David S. Miller" , Jiri Slaby Subject: [PATCH 3.12 099/111] tcp: fix cwnd undo on DSACK in F-RTO Date: Mon, 23 Jun 2014 10:32:14 +0200 Message-Id: X-Mailer: git-send-email 2.0.0 In-Reply-To: <55d5f044a1fc96a74e4470e318c0a24f27a9ab7e.1403512280.git.jslaby@suse.cz> References: <55d5f044a1fc96a74e4470e318c0a24f27a9ab7e.1403512280.git.jslaby@suse.cz> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yuchung Cheng 3.12-stable review patch. If anyone has any objections, please let me know. =============== [ Upstream commit 0cfa5c07d6d1d7f8e710fc671c5ba1ce85e09fa4 ] This bug is discovered by an recent F-RTO issue on tcpm list https://www.ietf.org/mail-archive/web/tcpm/current/msg08794.html The bug is that currently F-RTO does not use DSACK to undo cwnd in certain cases: upon receiving an ACK after the RTO retransmission in F-RTO, and the ACK has DSACK indicating the retransmission is spurious, the sender only calls tcp_try_undo_loss() if some never retransmisted data is sacked (FLAG_ORIG_DATA_SACKED). The correct behavior is to unconditionally call tcp_try_undo_loss so the DSACK information is used properly to undo the cwnd reduction. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Jiri Slaby --- net/ipv4/tcp_input.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 068c8fb0d158..0e8af08a98fc 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2633,13 +2633,12 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) bool recovered = !before(tp->snd_una, tp->high_seq); if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ - if (flag & FLAG_ORIG_SACK_ACKED) { - /* Step 3.b. A timeout is spurious if not all data are - * lost, i.e., never-retransmitted data are (s)acked. - */ - tcp_try_undo_loss(sk, true); + /* Step 3.b. A timeout is spurious if not all data are + * lost, i.e., never-retransmitted data are (s)acked. + */ + if (tcp_try_undo_loss(sk, flag & FLAG_ORIG_SACK_ACKED)) return; - } + if (after(tp->snd_nxt, tp->high_seq) && (flag & FLAG_DATA_SACKED || is_dupack)) { tp->frto = 0; /* Loss was real: 2nd part of step 3.a */ -- 2.0.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/