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

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Message-Id: <20111221.155615.990885397853981125.davem@davemloft.net>
Date:	Wed, 21 Dec 2011 15:56:15 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	steffen.klassert@...unet.com
Cc:	timo.teras@....fi, netdev@...r.kernel.org
Subject: Re: linux-3.0.x regression with ipv4 routes having mtu

From: Steffen Klassert <steffen.klassert@...unet.com>
Date: Wed, 21 Dec 2011 09:56:16 +0100

> On Tue, Dec 20, 2011 at 01:35:42PM -0500, David Miller wrote:
>> From: Steffen Klassert <steffen.klassert@...unet.com>
>> Date: Tue, 20 Dec 2011 08:18:43 +0100
>> 
>> > On Tue, Dec 20, 2011 at 02:03:55AM -0500, David Miller wrote:
>> >> From: Timo Teräs <timo.teras@....fi>
>> >> Date: Tue, 20 Dec 2011 08:53:09 +0200
>> >> 
>> >> > Or maybe I missed the place where that updated would happen?
>> >> 
>> >> It should happen on every routing cache lookup hit just like we
>> >> validate the peer for redirect information.
>> > 
>> > The problem is that we need to do a route cache lookup to
>> > validate the peer informations. This does not happen if
>> > somebody adds a new route. I tried already to add a pmtu specific
>> > generation id and it appears to not solve the problem. We would
>> > still need to overwrite the cached value if we add a route with mtu.
>> 
>> Why?
>> 
>> Every use of a routing cache entry does a dst_check() or a routing
>> cache lookup.
>> 
>> You can check the generation ID in both locations, and if the
>> comparison fails then you force the routing cache entry to be killed
>> and the caller performs a lookup.  At that time the refreshing of the
>> new FIB entry will be realized.
> 
> My decscription was a bit missleading, sorry. This seems to be not
> even related to pmtu handling. It's just that we don't use the
> user configured metrics on the fib entry if we find an inetpeer
> with metrics that are not in INETPEER_METRICS_NEW state when we
> initialize the routing metrics in rt_init_metrics(). I tried to add
> a route with a hoplimit, this has also no effect if the metrics on
> the inetpeer are not new.

Ok, so what you're saying is that we need a way to invalidate inetpeer
entries, or at least invalidate their cached metrics and set
INETPEER_METRICS_NEW once more.
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