Hi Eric, On 13.01.2017 18:35, Eric Dumazet wrote: > On Fri, 2017-01-13 at 18:01 +0300, Alexey Kodanev wrote: >> Hi, >> >> Got the issue when running LTP/netstress test on localhost with mss >> greater than the send window advertised by client (right after 3WHS). >> Here is the testscenario that can reproduce this: > Hi Alexey > > So this is a combination of Fastopen + small window + large MSS ?
Yeah, this happens only in the beginning, after first ack from client. Later window gets lager than mss and it doesn't happen. > > I would rather not force burning tons of coal or other fossil fuel, > by making each tcp_sendmsg() done by billions of linux devices more > expensive, only to accommodate for some LTP test doing something not > sensible ;) > > Fact that you removed one condition in the BUG_ON() might hide another > issue later in the path. > > I would suggest to clamp MSS to half the initial window, but I guess > this is impractical since window in SYN/SYNACK are not scaled. > Care to send a packetdrill test so that we have a clear picture of what > is going on ? Is it capable of making two connections in the single test, one after another? Thanks, Alexey
