From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 6 Apr 2018 09:47:14 +0200 From: Greg Kroah-Hartman To: Stefano Brivio Cc: Ben Hutchings , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Petr Vorel , Alexey Kodanev , "David S. Miller" , Sasha Levin , Steffen Klassert Subject: Re: [PATCH 4.4 92/97] ip6_vti: adjust vti mtu according to mtu of lower device Message-ID: <20180406074714.GA3127@kroah.com> References: <20180323094157.535925724@linuxfoundation.org> <20180323094202.622913188@linuxfoundation.org> <1522800556.2654.158.camel@codethink.co.uk> <20180405173636.5765efcf@epycfail> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180405173636.5765efcf@epycfail> User-Agent: Mutt/1.9.4 (2018-02-28) X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Apr 05, 2018 at 05:36:36PM +0200, Stefano Brivio wrote: > On Wed, 04 Apr 2018 01:09:16 +0100 > Ben Hutchings 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 > > > > > > > > > [ 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