xen-netfront: Fix hang on device removal

commit c2d2e6738a209f0f9dffa2dc8e7292fc45360d61 upstream.

A toolstack may delete the vif frontend and backend xenstore entries
while xen-netfront is in the removal code path.  In that case, the
checks for xenbus_read_driver_state would return XenbusStateUnknown, and
xennet_remove would hang indefinitely.  This hang prevents system
shutdown.

xennet_remove must be able to handle XenbusStateUnknown, and
netback_changed must also wake up the wake_queue for that state as well.

Fixes: 5b5971df3bc2 ("xen-netfront: remove warning when unloading module")

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Cc: Eduardo Otubo <otubo@redhat.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index c980cdb..a9ba9fe 100644 (file)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -2008,7 +2008,10 @@ static void netback_changed(struct xenbus_device *dev,
        case XenbusStateInitialised:
        case XenbusStateReconfiguring:
        case XenbusStateReconfigured:
+               break;
+
        case XenbusStateUnknown:
+               wake_up_all(&module_unload_q);
                break;
 
        case XenbusStateInitWait:
@@ -2139,7 +2142,9 @@ static int xennet_remove(struct xenbus_device *dev)
                xenbus_switch_state(dev, XenbusStateClosing);
                wait_event(module_unload_q,
                           xenbus_read_driver_state(dev->otherend) ==
-                          XenbusStateClosing);
+                          XenbusStateClosing ||
+                          xenbus_read_driver_state(dev->otherend) ==
+                          XenbusStateUnknown);
 
                xenbus_switch_state(dev, XenbusStateClosed);
                wait_event(module_unload_q,