netdev - Re: Problematic commits in the ipsec tree

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Message-ID: <20130826104627.GC30508@order.stressinduktion.org>
Date:	Mon, 26 Aug 2013 12:46:27 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Problematic commits in the ipsec tree

On Mon, Aug 26, 2013 at 11:41:45AM +0200, Steffen Klassert wrote:
> On Fri, Aug 23, 2013 at 02:49:11PM +0200, Hannes Frederic Sowa wrote:
> > 
> > This could be the replacement for patch 1/2 to reassemble old behaviour
> > without touching ip6_skb_dst_mtu if the socket type is not an IPv6 one.
> > 
> > I would still like to look if we could correctly handle *_PMTUDISC_PROBE one
> > day and fallback to dst_mtu(dst->path) if possible. So I don't know if
> > removing xfrm_skb_dst_mtu is good style and would just make churn in the git
> > history. What do you think?
> 
> Currently I think we can call dst_mtu() unconditionally from
> __xfrm6_output(), then we would not need xfrm_skb_dst_mtu().
> But this needs further investigation, IPsec pmtu discovery
> was frequently broken in the past and I don't want to break
> it again.

My idea was something like

|	  struct ipv6_pinfo *np = ...;
|         int mtu = (np && np->pmtudisc == IPV6_PMTUDISC_PROBE) ?
|                   dst_mtu(skb_dst(skb)->path) : dst_mtu(skb_dst(skb));

But I don't know if this does actually anything good and where the dispatch of
dst_mtu goes to. My idea was to avoid the dst_metric_raw(dst, RTAX_MTU)
call in xfrm_mtu in case of IPV6_PMTUDISC_PROBE.

> > [PATCH ipsec 1/2] xfrm: revert ipv4 mtu determination to dst_mtu
> > 
> > In commit 0ea9d5e3e0e03a63b11392f5613378977dae7eca ("xfrm: introduce
> > helper for safe determination of mtu") I switched the determination of
> > ipv4 mtus from dst_mtu to ip_skb_dst_mtu. This was an error because in
> > case of IP_PMTUDISC_PROBE we fall back to the interface mtu, which is
> > never correct for ipv4 ipsec.
> > 
> > This patch partly reverts 0ea9d5e3e0e03a63b11392f5613378977dae7eca
> > ("xfrm: introduce helper for safe determination of mtu").
> > 
> 
> I think with this and you other patch, we get the all the
> interfamily tunnel problems fixed for now. Everything else
> should be done in ipsec-next.

Fully ACK.

> Please resend the whole patchset, so we can get it fixed soon.
> 
> Tanks a lot!

Sorry for holding back your tree for so long to get merged.

Thanks,

  Hannes

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