Xen users - Mar 2013 - Race condition in sending gratuitous ARP for live migration ?

Hi,


So, the issue is a fairly common one: Network doesn''t work for like a
minute or so after a live migration.
The setup is a debian wheezy dom0 with xen 4.1.2 running 3.6.11
kernel. The domU is a Ubuntu 12.04 with a 3.2 kernel. The networking
setup uses bridges on the dom0. I also made sure that the bridge
forwarding delay is set to 0.

The VM doesn''t initiate any network activity on its own, so
it''s
solely relying on the gratuitous ARP to be sent for the various place
(switch and dom0 bridges) to be updated.

I confirmed that the gratuitous ARP is sent by the domU after
migration by using tcpdump. I can also see it on the vif on the dom0.
But I can''t see it on the bridge interface in the dom0, nor on the
network itself. I also confirmed that it I make the domU send
gratuitous ARP continuously using arping, the it works fine.

So I think the gratuitous ARP is sent a bit too early, before it''s
ready to be forwarded around with the dom0.

Any idea how I can check and correct this ?


Cheers,

     Sylvain

Hi,

So responding to myself: There is indeed a race condition ... and it
was fixed 1.5 years ago by Laszlo Ersek.
Unfortunately the fix isn''t present in the Ubuntu 12.04 LTS kernel,
nor in the stable 3.2 tree :(

http://xen.1045712.n5.nabble.com/lost-gARP-after-live-migration-td4531697.html

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/net/xen-netfront.c?id=08e34eb14fe4cfd934b5c169a7682a969457c4ea

Cheers,

    Sylvain

On Wed, 2013-03-13 at 14:11 +0000, Sylvain Munaut wrote:
> Hi,
> 
> So responding to myself: There is indeed a race condition ... and it
> was fixed 1.5 years ago by Laszlo Ersek.
> Unfortunately the fix isn''t present in the Ubuntu 12.04 LTS
kernel,
> nor in the stable 3.2 tree :(
Can you file a bug with Ubuntu please?

Ian.

Hi,
>> So responding to myself: There is indeed a race condition ... and it
>> was fixed 1.5 years ago by Laszlo Ersek.
>> Unfortunately the fix isn''t present in the Ubuntu 12.04 LTS
kernel,
>> nor in the stable 3.2 tree :(
>
> Can you file a bug with Ubuntu please?
Already did :)

I''d like to not have to maintain my own kernel for the VMs :p

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1154608

Cheers,

   Sylvain