netdev - Re: IPv6 path discovery oddities - flushing the routing cache resolves

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Date:	Sat, 19 Oct 2013 22:24:14 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Valentijn Sessink <valentyn@...b.net>
Cc:	netdev@...r.kernel.org,
	"Steinar H. Gunderson" <sgunderson@...foot.com>
Subject: Re: IPv6 path discovery oddities - flushing the routing cache resolves

On Sat, Oct 19, 2013 at 04:24:59PM +0200, Valentijn Sessink wrote:
> op 19-10-13 12:12, Steinar H. Gunderson schreef:
> >Thanks so much for looking into this! It's great that to hear that it's not
> >just me being weird =)
> 
> I'm not sure the patch addresses weirdness ;-P
> 
> On the more serious side: I have this problem with a 3.8.0 kernel 
> (Ubuntu 12.04 with updated kernel). I saw that you (Steinar) experience 
> this with 3.10 and 3.11, iirc. I'm a little bit worried by the fact that 
> this has not been seen for at least six months - and now suddenly pops up.
> 
> Does anyone have an idea when this race condition was introduced?

Do a bisect. ;)

I had a look at the history but could not find a single commit
to blame. Even reference counting changes (e.g. removal of neighbour
caching in routes) or something in the way the socket release callbacks
are processed by tcp could introduce a way where these problems are more
likely to happen. I wondered, too.

A lot of people of the IPv6 community often state that mtu discovery is broken
because of filtering packet_too_bigs. Maybe most people assumed broken
firewalls and did not actual check if it is the kernels problem. So, thanks
again for reporting this issue.

Greetings,

  Hannes

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