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Date:   Tue, 26 Mar 2019 10:21:09 +0900
From:   Greg KH <>
To:     Arnd Bergmann <>
Cc:, "David S. Miller" <>,
        Gerrit Renker <>,
        Eric Dumazet <>,
        Alexey Kuznetsov <>,
        Hideaki YOSHIFUJI <>,
        Neal Cardwell <>,
        Yuchung Cheng <>,
        Wei Wang <>,
        Ilya Lesokhin <>,
        Priyaranjan Jha <>,
        Soheil Hassas Yeganeh <>,
        Yafang Shao <>,,,
Subject: Re: [BACKPORT 4.4.y 18/25] tcp/dccp: drop SYN packets if accept
 queue is full

On Fri, Mar 22, 2019 at 04:44:09PM +0100, Arnd Bergmann wrote:
> From: Eric Dumazet <>
> Per listen(fd, backlog) rules, there is really no point accepting a SYN,
> sending a SYNACK, and dropping the following ACK packet if accept queue
> is full, because application is not draining accept queue fast enough.
> This behavior is fooling TCP clients that believe they established a
> flow, while there is nothing at server side. They might then send about
> 10 MSS (if using IW10) that will be dropped anyway while server is under
> stress.
> Signed-off-by: Eric Dumazet <>
> Acked-by: Neal Cardwell <>
> Acked-by: Yuchung Cheng <>
> Signed-off-by: David S. Miller <>
> (cherry picked from commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071)

Also queued up for 4.9.y

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