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Date:   Mon, 18 Jan 2021 20:02:21 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Enke Chen <enkechen2020@gmail.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Eric Dumazet <edumazet@google.com>,
        Yuchung Cheng <ycheng@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        Neal Cardwell <ncardwell@google.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Jonathan Maxwell <jmaxwell37@gmail.com>,
        William McCall <william.mccall@gmail.com>
Subject: Re: [PATCH net v2] tcp: fix TCP_USER_TIMEOUT with zero window
Message-ID: <20210118200221.73033add@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
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On Fri, 15 Jan 2021 14:30:58 -0800 Enke Chen wrote:
> From: Enke Chen <enchen@paloaltonetworks.com>
> 
> The TCP session does not terminate with TCP_USER_TIMEOUT when data
> remain untransmitted due to zero window.
> 
> The number of unanswered zero-window probes (tcp_probes_out) is
> reset to zero with incoming acks irrespective of the window size,
> as described in tcp_probe_timer():
> 
>     RFC 1122 4.2.2.17 requires the sender to stay open indefinitely
>     as long as the receiver continues to respond probes. We support
>     this by default and reset icsk_probes_out with incoming ACKs.
> 
> This counter, however, is the wrong one to be used in calculating the
> duration that the window remains closed and data remain untransmitted.
> Thanks to Jonathan Maxwell <jmaxwell37@gmail.com> for diagnosing the
> actual issue.
> 
> In this patch a new timestamp is introduced for the socket in order to
> track the elapsed time for the zero-window probes that have not been
> answered with any non-zero window ack.
> 
> Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
> Reported-by: William McCall <william.mccall@gmail.com>
> Co-developed-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Enke Chen <enchen@paloaltonetworks.com>
> Reviewed-by: Yuchung Cheng <ycheng@google.com>
> Reviewed-by: Eric Dumazet <edumazet@google.com>

I take it you got all these tags off-list? I don't see them on the v1
discussion.

Applied to net, thanks!