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Date:   Tue, 26 Mar 2019 10:21:09 +0900
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     stable@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Gerrit Renker <gerrit@erg.abdn.ac.uk>,
        Eric Dumazet <edumazet@google.com>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Neal Cardwell <ncardwell@google.com>,
        Yuchung Cheng <ycheng@google.com>,
        Wei Wang <weiwan@google.com>,
        Ilya Lesokhin <ilyal@mellanox.com>,
        Priyaranjan Jha <priyarjha@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Yafang Shao <laoar.shao@gmail.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, dccp@vger.kernel.org
Subject: Re: [BACKPORT 4.4.y 18/25] tcp/dccp: drop SYN packets if accept
 queue is full
Message-ID: <20190326012109.GD29420@kroah.com>
References: <20190322154425.3852517-1-arnd@arndb.de>
 <20190322154425.3852517-19-arnd@arndb.de>
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On Fri, Mar 22, 2019 at 04:44:09PM +0100, Arnd Bergmann wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> 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 <edumazet@google.com>
> Acked-by: Neal Cardwell <ncardwell@google.com>
> Acked-by: Yuchung Cheng <ycheng@google.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> (cherry picked from commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071)

Also queued up for 4.9.y