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.