From: Chris Lalancette <clalance@redhat.com>
Date: Thu, 5 Mar 2009 14:18:53 +0100
Subject: [xen] fix crash when modprobe xen-vnif in a KVM guest
Message-id: 49AFD13D.8080407@redhat.com
O-Subject: [RHEL5.4 PATCH]: Fix crash when modprobe xen-vnif in a KVM guest
Bugzilla: 487691
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Rik van Riel <riel@redhat.com>
RH-Acked-by: Justin M. Forbes <jforbes@redhat.com>
RH-Acked-by: Justin M. Forbes <jforbes@redhat.com>

All,
     When you attempt to modprobe the xen-vnif driver on a machine not
supporting Xen (either bare-metal, or under KVM hypervisor, etc), the modprobe
fails with ENODEV.  This is the right behavior.  However, if you then shut down
the machine, you get an OOPs on shutdown.  This is because the xen-vnif init()
routine wasn't properly unregistering notifiers on failure, leading to the OOPs.
 The solution is to unregister the notifiers on failure, which prevents the
OOPs.  This patch is a backport of xen-unstable c/s 14622 and linux-2.6.18-hg
c/s 803, and fixes the problem for me in testing.  This should solve BZ 487691.
 Please review and ACK.

--
Chris Lalancette

diff --git a/drivers/xen/netfront/netfront.c b/drivers/xen/netfront/netfront.c
index 4df5cca..f037811 100644
--- a/drivers/xen/netfront/netfront.c
+++ b/drivers/xen/netfront/netfront.c
@@ -2130,6 +2130,8 @@ static struct notifier_block notifier_netdev = {
 
 static int __init netif_init(void)
 {
+	int err;
+
 	if (!is_running_on_xen())
 		return -ENODEV;
 
@@ -2151,7 +2153,12 @@ static int __init netif_init(void)
 	(void)register_inetaddr_notifier(&notifier_inetdev);
 	(void)register_netdevice_notifier(&notifier_netdev);
 
-	return xenbus_register_frontend(&netfront);
+	err = xenbus_register_frontend(&netfront);
+	if (err) {
+		unregister_netdevice_notifier(&notifier_netdev);
+		unregister_inetaddr_notifier(&notifier_inetdev);
+	}
+	return err;
 }
 module_init(netif_init);
 
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index d4c28dd..4e3f730 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -667,10 +667,17 @@ static int xenbus_probe_node(struct xen_bus_type *bus,
 	if (err)
 		goto fail;
 
-	device_create_file(&xendev->dev, &dev_attr_nodename);
-	device_create_file(&xendev->dev, &dev_attr_devtype);
+	err = device_create_file(&xendev->dev, &dev_attr_nodename);
+	if (err)
+		goto unregister;
+	err = device_create_file(&xendev->dev, &dev_attr_devtype);
+	if (err)
+		goto unregister;
 
 	return 0;
+unregister:
+	device_remove_file(&xendev->dev, &dev_attr_nodename);
+	device_remove_file(&xendev->dev, &dev_attr_devtype);
 fail:
 	kfree(xendev);
 	return err;
@@ -1173,7 +1180,15 @@ static int __init xenbus_probe_init(void)
 	}
 
 	/* Register ourselves with the kernel device subsystem */
-	device_register(&xenbus_frontend.dev);
+	if (!xenbus_frontend.error) {
+		xenbus_frontend.error = device_register(&xenbus_frontend.dev);
+		if (xenbus_frontend.error) {
+			bus_unregister(&xenbus_frontend.bus);
+			printk(KERN_WARNING
+			       "XENBUS: Error registering frontend device: %i\n",
+			       xenbus_frontend.error);
+		}
+	}
 #ifdef CONFIG_XEN
 	device_register(&xenbus_backend.dev);
 #endif