netdev - Re: [PATCH net] tcp: update skb->skb

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Message-ID: <6c8fd260-f2a1-4377-2dd8-5975249ab597@huawei.com>
Date:   Thu, 14 Sep 2017 16:17:20 +0800
From:   liujian <liujian56@...wei.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
CC:     <edumazet@...gle.com>, <ycheng@...gle.com>, <hkchu@...gle.com>,
        <netdev@...r.kernel.org>, <weiyongjun1@...wei.com>,
        wangkefeng 00227729 <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH net] tcp: update skb->skb_mstamp more carefully



On 2017/9/14 11:30, Eric Dumazet worte:
> From: Eric Dumazet <edumazet@...gl.com>
> 
> 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.
> 
>

I test  on 4.13, it can work.
thank you!