xen/blkfront: allow xenbus state transition to Closing->Closed when not Connected

This situation can occur when attempting to attach a block device whose
backend is an empty physical CD-ROM driver. The backend in this case
will go directly from the Initialising state to Closing->Closed.
Previously this would result in a NULL pointer deref on info->gd
(xenbus_dev_fatal does not return as a1a15ac5 seems to expect)

Cc: stable@kernel.org
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 8f905089b72b..6971a12e8b9b 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -977,8 +977,10 @@ static void backend_changed(struct xenbus_device *dev,
                 break;
 
         case XenbusStateClosing:
-                if (info->gd == NULL)
-                        xenbus_dev_fatal(dev, -ENODEV, "gd is NULL");
+                if (info->gd == NULL) {
+                        xenbus_frontend_closed(dev);
+                        break;
+                }
                 bd = bdget_disk(info->gd, 0);
                 if (bd == NULL)
                         xenbus_dev_fatal(dev, -ENODEV, "bdget failed");