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SubjectRe: [PATCH 4.4 92/97] ip6_vti: adjust vti mtu according to mtu of lower device
On Thu, Apr 05, 2018 at 05:36:36PM +0200, Stefano Brivio wrote:
> On Wed, 04 Apr 2018 01:09:16 +0100
> Ben Hutchings <ben.hutchings@codethink.co.uk> wrote:
>
> > On Fri, 2018-03-23 at 10:55 +0100, Greg Kroah-Hartman wrote:
> > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > From: Alexey Kodanev <alexey.kodanev@oracle.com>
> > >
> > >
> > > [ Upstream commit 53c81e95df1793933f87748d36070a721f6cb287 ]
> > [...]
> >
> > There are a couple of follow-ups to this:
> >
> > c6741fbed6dc vti6: Properly adjust vti6 MTU from MTU of lower device
> > 7a67e69a339a vti6: Keep set MTU on link creation or change, validate it
> >
> > The second of those will fail to build on branches older than 4.10
> > though. It might be better to revert this one instead.
>
> Thanks Ben for spotting this.
>
> Actually,
> 53c81e95df17 ("ip6_vti: adjust vti mtu according to mtu of lower device")
> alone improves things already, despite being "fixed" by
> c6741fbed6dc ("vti6: Properly adjust vti6 MTU from MTU of lower device")
>
> With just 53c81e95df17 the MTU of a vti6 interface will be somewhat
> linked to the MTU of the lower layer, but will be underestimated.
>
> With c6741fbed6dc the calculation of MTU from lower layer will be
> accurate instead.
>
> However, without
> 7a67e69a339a ("vti6: Keep set MTU on link creation or change, validate it")
> but with
> 53c81e95df17 ("ip6_vti: adjust vti mtu according to mtu of lower device")
> assignment of MTU on link change is discarded, so this would actually
> introduce a bug.
>
> Fixing
> 7a67e69a339a ("vti6: Keep set MTU on link creation or change, validate it")
> for 4.4 up to 4.9 is trivial, we simply need to adjust for the lack of
> b96f9afee4eb ("ipv4/6: use core net MTU range checking")
> and reflect the change introduced by
> f8a554b4aa96 ("vti6: Fix dev->max_mtu setting").
>
> So, Greg, here comes the backport of
> 7a67e69a339a ("vti6: Keep set MTU on link creation or change, validate it")
> based on latest linux-4.4.y branch, in case you want to keep the existing
> change and add the follow-ups on top. Please let me know if I should submit
> it formally.

Ick, that's a mess. How about I just revert this patch from the stable
trees, and then someone sends me either a list of git commits to apply,
or patches, for the different trees if it's really needed?

thanks,

greg k-h

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