From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDDFEC636C9 for ; Thu, 15 Jul 2021 19:24:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C2BA761158 for ; Thu, 15 Jul 2021 19:24:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244079AbhGOT1g (ORCPT ); Thu, 15 Jul 2021 15:27:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:46400 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243600AbhGOTJ6 (ORCPT ); Thu, 15 Jul 2021 15:09:58 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id BEECB613CA; Thu, 15 Jul 2021 19:06:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626375961; bh=b8+TtQfQusBnMO1Kjs2b7DG2qKOuVMUGj9zIJNCEjKU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FQ385CR3rm0RSLlJoG17HQaP4mHunUOe5/Pwuw2l7dqj0b2LT0CNngfdxKeRl6CWR 0i85a5jpdzNtACt/UCBxglA882MJ25GH6oMCQFKU4gjdL5OSW0EWoEPcSZnQOrB/4p MYRttDY1Qv7pTGPCIbc/hVjyGuyJxHM59KnYco0c= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, mingkun bian , Yuchung Cheng , Neal Cardwell , Eric Dumazet , "David S. Miller" , Sasha Levin Subject: [PATCH 5.13 065/266] net: tcp better handling of reordering then loss cases Date: Thu, 15 Jul 2021 20:37:00 +0200 Message-Id: <20210715182625.752206356@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210715182613.933608881@linuxfoundation.org> References: <20210715182613.933608881@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yuchung Cheng [ Upstream commit a29cb6914681a55667436a9eb7a42e28da8cf387 ] This patch aims to improve the situation when reordering and loss are ocurring in the same flight of packets. Previously the reordering would first induce a spurious recovery, then the subsequent ACK may undo the cwnd (based on the timestamps e.g.). However the current loss recovery does not proceed to invoke RACK to install a reordering timer. If some packets are also lost, this may lead to a long RTO-based recovery. An example is https://groups.google.com/g/bbr-dev/c/OFHADvJbTEI The solution is to after reverting the recovery, always invoke RACK to either mount the RACK timer to fast retransmit after the reordering window, or restarts the recovery if new loss is identified. Hence it is possible the sender may go from Recovery to Disorder/Open to Recovery again in one ACK. Reported-by: mingkun bian Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- net/ipv4/tcp_input.c | 45 +++++++++++++++++++++++++------------------- 1 file changed, 26 insertions(+), 19 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 4cf4dd532d1c..bc266514ce58 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2816,8 +2816,17 @@ static void tcp_process_loss(struct sock *sk, int flag, int num_dupack, *rexmit = REXMIT_LOST; } +static bool tcp_force_fast_retransmit(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + return after(tcp_highest_sack_seq(tp), + tp->snd_una + tp->reordering * tp->mss_cache); +} + /* Undo during fast recovery after partial ACK. */ -static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una) +static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una, + bool *do_lost) { struct tcp_sock *tp = tcp_sk(sk); @@ -2842,7 +2851,9 @@ static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una) tcp_undo_cwnd_reduction(sk, true); NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); tcp_try_keep_open(sk); - return true; + } else { + /* Partial ACK arrived. Force fast retransmit. */ + *do_lost = tcp_force_fast_retransmit(sk); } return false; } @@ -2866,14 +2877,6 @@ static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag) } } -static bool tcp_force_fast_retransmit(struct sock *sk) -{ - struct tcp_sock *tp = tcp_sk(sk); - - return after(tcp_highest_sack_seq(tp), - tp->snd_una + tp->reordering * tp->mss_cache); -} - /* Process an event, which can update packets-in-flight not trivially. * Main goal of this function is to calculate new estimate for left_out, * taking into account both packets sitting in receiver's buffer and @@ -2943,17 +2946,21 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, if (!(flag & FLAG_SND_UNA_ADVANCED)) { if (tcp_is_reno(tp)) tcp_add_reno_sack(sk, num_dupack, ece_ack); - } else { - if (tcp_try_undo_partial(sk, prior_snd_una)) - return; - /* Partial ACK arrived. Force fast retransmit. */ - do_lost = tcp_force_fast_retransmit(sk); - } - if (tcp_try_undo_dsack(sk)) { - tcp_try_keep_open(sk); + } else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost)) return; - } + + if (tcp_try_undo_dsack(sk)) + tcp_try_keep_open(sk); + tcp_identify_packet_loss(sk, ack_flag); + if (icsk->icsk_ca_state != TCP_CA_Recovery) { + if (!tcp_time_to_recover(sk, flag)) + return; + /* Undo reverts the recovery state. If loss is evident, + * starts a new recovery (e.g. reordering then loss); + */ + tcp_enter_recovery(sk, ece_ack); + } break; case TCP_CA_Loss: tcp_process_loss(sk, flag, num_dupack, rexmit); -- 2.30.2