Re: [Xen-devel] [PATCH net-next v4] xen-netfront: delay gARP until backend switches to Connected

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.12.11 at 12:48, Laszlo Ersek <lersek@xxxxxxxxxx> wrote:
> After a guest is live migrated, the xen-netfront driver emits a gratuitous
> ARP message, so that networking hardware on the target host's subnet can
> take notice, and public routing to the guest is re-established. However,
> if the packet appears on the backend interface before the backend is added
> to the target host's bridge, the packet is lost, and the migrated guest's
> peers become unable to talk to the guest.
> 
> A sufficient two-parts condition to prevent the above is:
> 
> (1) ensure that the backend only moves to Connected xenbus state after its
> hotplug scripts completed, ie. the netback interface got added to the
> bridge; and
> 
> (2) ensure the frontend only queues the gARP when it sees the backend move
> to Connected.
> 
> These two together provide complete ordering. Sub-condition (1) is already
> satisfied by commit f942dc2552b8 in Linus' tree, based on commit
> 6b0b80ca7165 from [1].
> 
> In general, the full condition is sufficient, not necessary, because,
> according to [2], live migration has been working for a long time without
> satisfying sub-condition (2). However, after 6b0b80ca7165 was backported
> to the RHEL-5 host to ensure (1), (2) still proved necessary in the RHEL-6
> guest. This patch intends to provide (2) for upstream.
> 
> The Reviewed-by line comes from [3].
> 
> [1] 
> git://xenbits.xen.org/people/ianc/linux-2.6.git#upstream/dom0/backend/netbac
> k-history
> [2] http://old-list-archives.xen.org/xen-devel/2011-06/msg01969.html 
> [3] http://old-list-archives.xen.org/xen-devel/2011-07/msg00484.html 
> 
> Signed-off-by: Laszlo Ersek <lersek@xxxxxxxxxx>
> Reviewed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Wouldn't all of this equally apply to the 2.6.18 kernel and its derivates?

Jan

> ---
>  drivers/net/xen-netfront.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index d29365a..f033656 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1646,7 +1646,6 @@ static void netback_changed(struct xenbus_device *dev,
>       case XenbusStateInitialised:
>       case XenbusStateReconfiguring:
>       case XenbusStateReconfigured:
> -     case XenbusStateConnected:
>       case XenbusStateUnknown:
>       case XenbusStateClosed:
>               break;
> @@ -1657,6 +1656,9 @@ static void netback_changed(struct xenbus_device *dev,
>               if (xennet_connect(netdev) != 0)
>                       break;
>               xenbus_switch_state(dev, XenbusStateConnected);
> +             break;
> +
> +     case XenbusStateConnected:
>               netif_notify_peers(netdev);
>               break;
>  
> -- 
> 1.7.4.4
> 
> 
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> http://lists.xensource.com/xen-devel 




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