netdev - Re: BUG: jumbo frames broken after commit xen-netfront: Fix race between device setup and open

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Date:   Thu, 14 Jun 2018 17:43:49 +0200
From:   Javier Martinez Canillas <javier@...hile0.org>
To:     Andrew Jeddeloh <andrew.jeddeloh@...hat.com>,
        Laura Abbott <labbott@...hat.com>, dustymabe@...hat.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org
Cc:     netdev <netdev@...r.kernel.org>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org
Subject: Re: BUG: jumbo frames broken after commit xen-netfront: Fix race
 between device setup and open

Hi Andrew,

On Wed, Jun 6, 2018 at 6:29 PM, Andrew Jeddeloh
<andrew.jeddeloh@...hat.com> wrote:
> Hi all,
>
> The patch "xen-netfront: Fix race between device setup and open" seems
> to have introduced a regression preventing setting MTU's larger than
> 1500. We experienced this downstream with Container Linux and
> confirmed with Fedora 28 as well.
>
> It's commit f599c64fdf7d9c108e8717fb04bc41c680120da4 in the linux-stable tree.
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=f599c64fdf7d9c108e8717fb04bc41c680120da4
>
> Downstream bugs:
> https://github.com/coreos/bugs/issues/2443
> https://bugzilla.redhat.com/show_bug.cgi?id=1584216
>
> We've confirmed that reverting that commit fixes the bug. It be
> reliably can be reproduced on AWS with t2.micro instances (and
> presumably other systems using the same driver). Both using
> systemd-networkd to set the mtu and manual ip link commands cause the
> link to repsond with "Invalid argument" when trying to set the MTU >
> 1500.
>
> I'm not sure why that commit introduced the regression.
>
> Please let me know if there's any more information that would be helpful.
>
> - Andrew

I'm adding some relevant people to the CC list to bring more attention
on this regression.

The get_maintainer.pl script is very useful to get some hints on who
should be copied, i.e:

$ ./scripts/get_maintainer.pl -f drivers/net/xen-netfront.c

Best regards,
Javier