netdev - Re: TCP connection closed without FIN or RST

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Date:   Fri, 03 Nov 2017 09:05:44 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vitaly Davidovich <vitalyd@...il.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: TCP connection closed without FIN or RST

On Fri, 2017-11-03 at 11:13 -0400, Vitaly Davidovich wrote:
> Ok, an interesting finding.  The client was originally running with
> SO_RCVBUF of 75K (apparently someone decided to set that for some
> unknown reason).  I tried the test with a 1MB recv buffer and
> everything works perfectly! The client responds with 0 window alerts,
> the server just hits the persist condition and sends keep-alive
> probes; the client continues answering with a 0 window up until it
> wakes up and starts processing data in its receive buffer.  At that
> point, the window opens up and the server sends more data.  Basically,
> things look as one would expect in this situation :).
> 
> /proc/sys/net/ipv4/tcp_rmem is 131072  1048576   20971520.  The
> conversation flows normally, as described above, when I change the
> client's recv buf size to 1048576.  I also tried 131072, but that
> doesn't work - same retrans/no ACKs situation.
> 
> I think this eliminates (right?) any middleware from the equation.
> Instead, perhaps it's some bad interaction between a low recv buf size
> and either some other TCP setting or TSO mechanics (LRO specifically).
> Still investigating further.

Just in case, have you tried a more recent linux kernel ?

I would rather not spend time on some problem that might already be
fixed.