netdev - Re: After a while of system running no incoming UDP any more?

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Date:   Tue, 25 Jul 2017 13:57:45 +0200
From:   Marc Haber <mh+netdev@...schlus.de>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: After a while of system running no incoming UDP any more?

Hi Paolo,

thanks for your answer. I appreciate that.

On Mon, Jul 24, 2017 at 04:19:10PM +0200, Paolo Abeni wrote:
> On Mon, 2017-07-24 at 14:09 +0200, Marc Haber wrote:
> > Before I begin running older kernels on productive systems, I would like
> > to ask wether there have been recent changes in the 4.11 => 4.12
> > development cycle that might cause an issue like that.
> 
> While there has been some activity regarding the UDP protocol lately,
> almost nothing touched UDP in the 4.11 release cycle.

4.11 is good, 4.12 is bad.

> The issue you describe looks similar to the bug fixed by the commit
> 9bd780f5e066 ("udp: fix poll()"), but the bugged code is only in later
> kernels. 

That one is in v4.13-rc1 and v4.13-rc2, but it doesn't apply to my 4.12
trees.

> > Any idea what might be happening here and what else I could try?
> 
> Once that a system enter the buggy status, do the packets reach the
> relevant socket's queue?
> 
> ss -u

That one only shows table headers on an unaffected system in normal
operation, right?

> nstat |grep -e Udp -e Ip
> 
> will help checking that.

An unaffected system will show UdpInDatagrams, right?

But where is the connection to the relevant socket's queue?

Greetings
Marc

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