netdev - Re: TCP connection closed without FIN or RST

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Date:   Wed, 01 Nov 2017 16:06:57 -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 Wed, 2017-11-01 at 22:22 +0000, Vitaly Davidovich wrote:
> Eric,
> 

> Yes I agree.  However the thing I’m still puzzled about is the client
> application is not reading/draining the recvq - ok, the client tcp
> stack should start advertising a 0 window size.  Does a 0 window size
> count against the tcp_retries2? Is that what you were alluding to in
> your first reply?
> 

Every time we receive an (valid) ACK, with a win 0 or not, the counter
of attempts is cleared, given the opportunity for the sender to send 15
more probes.
> 
> If it *does* count towards the retries limit then a RST doesn’t seem
> like a bad idea.  The client is responding with segments but the user
> app there just isn’t draining the data.  Presumably that RST has a
> good chance of reaching the client and then unblocking the read()
> there with a peer reset error.  Or am I missing something?
> 
> 
> If it doesn’t count towards the limit then I need to figure out why
> the 0 window size segments weren’t being sent by the client.

Yes please :)
> 
> 
> I will try to double check that the client was indeed advertising 0
> window size.  There’s nothing special about that machine - it’s a
> 4.1.35 kernel as well.  I wouldn’t expect the tcp stack there to be
> unresponsive just because the user app is sleeping.
>