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

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Date:   Thu, 21 Jun 2018 11:05:41 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Ross Lagerwall <ross.lagerwall@...rix.com>
Cc:     Javier Martinez Canillas <javier@...hile0.org>,
        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,
        netdev <netdev@...r.kernel.org>, xen-devel@...ts.xenproject.org
Subject: Re: BUG: jumbo frames broken after commit xen-netfront: Fix race
 between device setup and open

On 14/06/18 17:43, Javier Martinez Canillas wrote:
> 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

Ross, have you made any progress here? If not I'm thinking of reverting
your patch as I think the current problem is more severe than the one
your patch did address.


Juergen