From: Laszlo Ersek Date: Sun, 11 Dec 2011 01:48:59 +0000 (+0000) Subject: xen-netfront: delay gARP until backend switches to Connected X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=08e34eb14fe4cfd934b5c169a7682a969457c4ea;p=deliverable%2Flinux.git xen-netfront: delay gARP until backend switches to Connected 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/netback-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 Reviewed-by: Ian Campbell Signed-off-by: David S. Miller --- diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index 4312db8cdeab..0a59c57864f5 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -1709,7 +1709,6 @@ static void netback_changed(struct xenbus_device *dev, case XenbusStateInitialised: case XenbusStateReconfiguring: case XenbusStateReconfigured: - case XenbusStateConnected: case XenbusStateUnknown: case XenbusStateClosed: break; @@ -1720,6 +1719,9 @@ 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;