netdev - Re: linux-3.0.x regression with ipv4 routes having mtu

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Message-ID: <20111219135259.GK6348@secunet.com>
Date:	Mon, 19 Dec 2011 14:52:59 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Timo Teräs <timo.teras@....fi>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: linux-3.0.x regression with ipv4 routes having mtu

On Fri, Dec 16, 2011 at 04:30:26PM +0200, Timo Teräs wrote:
> On 12/16/2011 02:21 PM, Steffen Klassert wrote:
> > 
> > "ip route flush cache" does not even flush the routing cache,
> > it just markes the routing cache as invalid by changing the
> > rt_genid which make the old routes invisible. And since we don't
> > have rt_check_expire() anymore, we have to wait until we have
> > collected gc_thresh (1024) useless routes before rt_garbage_collect()
> > starts to remove some of them (btw. is this intentional).
> > 
> > I think we need a trigger in rt_cache_invalidate() that expires
> > all cached pmtu values similar to the routing cache entries.
> > For a moment I thought we could just reset the __rt_peer_genid
> > value back to zero to mark all cached pmtu values as expired,
> > but that's apparently not save to do. So I came to no conclusion
> > how to fix this today. Any ideas?
> 
> Oh, right. This problem is secondary. As long as the mtu value is
> reflected properly, I'll be happy :)
> 

Well, "ip route flush cache" flushed the cached pmtu informations
in 2.6.38 and before, now it does not do it anymore. I guess
some users rely on the old behaviour, so it would be nice if we
could restore it. I think we can fix this by adding a pmtu_genid,
exactly in the same way as we have now the redirect_genid.
I'll give this a try.
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