RE: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received

[David Laight]

From: Eric Dumazet
> Sent: 31 January 2020 22:54
> On 1/31/20 2:11 PM, Neal Cardwell wrote:
> 
> > I looked into fixing this, but my quick reading of the Linux
> > tcp_rcv_state_process() code is that it should behave correctly and
> > that a connection in FIN_WAIT_1 that receives a FIN/ACK should move to
> > TIME_WAIT.
> >
> > SeongJae, do you happen to have a tcpdump trace of the problematic
> > sequence where the "process A" ends up in FIN_WAIT_2 when it should be
> > in TIME_WAIT?
> >
> > If I have time I will try to construct a packetdrill case to verify
> > the behavior in this case.
> 
> Unfortunately you wont be able to reproduce the issue with packetdrill,
> since it involved packets being processed at the same time (race window)

You might be able to force the timing race by adding a sleep
in one of the code paths.

No good for a regression test, but ok for code testing.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)