From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] tcp: update skb->skb_mstamp more carefully Date: Fri, 15 Sep 2017 14:37:06 -0700 (PDT) Message-ID: <20170915.143706.992734259378949259.davem@davemloft.net> References: <3c750ac3-8739-89ed-ce41-d4cde755171e@huawei.com> <1505313647.15310.165.camel@edumazet-glaptop3.roam.corp.google.com> <1505359839.15310.209.camel@edumazet-glaptop3.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: liujian56@huawei.com, edumazet@google.com, ycheng@google.com, hkchu@google.com, netdev@vger.kernel.org, weiyongjun1@huawei.com, wangkefeng.wang@huawei.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:57528 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750841AbdIOVhH (ORCPT ); Fri, 15 Sep 2017 17:37:07 -0400 In-Reply-To: <1505359839.15310.209.camel@edumazet-glaptop3.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Wed, 13 Sep 2017 20:30:39 -0700 > From: Eric Dumazet > > liujian reported a problem in TCP_USER_TIMEOUT processing with a patch > in tcp_probe_timer() : > https://www.spinics.net/lists/netdev/msg454496.html > > After investigations, the root cause of the problem is that we update > skb->skb_mstamp of skbs in write queue, even if the attempt to send a > clone or copy of it failed. One reason being a routing problem. > > This patch prevents this, solving liujian issue. > > It also removes a potential RTT miscalculation, since > __tcp_retransmit_skb() is not OR-ing TCP_SKB_CB(skb)->sacked with > TCPCB_EVER_RETRANS if a failure happens, but skb->skb_mstamp has > been changed. > > A future ACK would then lead to a very small RTT sample and min_rtt > would then be lowered to this too small value. > > Tested: ... > Signed-off-by: Eric Dumazet > Reported-by: liujian Applied and queued up for -stable, thanks.