xen/netfront: fix waiting for xenbus state change

Commit 822fb18a ("xen-netfront: wait xenbus state change when load
module manually") added a new wait queue to wait on for a state change
when the module is loaded manually. Unfortunately there is no wakeup
anywhere to stop that waiting.

Instead of introducing a new wait queue rename the existing
module_unload_q to module_wq and use it for both purposes (loading and
unloading).

As any state change of the backend might be intended to stop waiting
do the wake_up_all() in any case when netback_changed() is called.

Fixes: 822fb18a ("xen-netfront: wait xenbus state change when load module manually")
Cc: <stable@vger.kernel.org> #4.18
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netfront.c

@@ -87,8 +87,7 @@ struct netfront_cb {
 /* IRQ name is queue name with "-tx" or "-rx" appended */
 #define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)
 
-static DECLARE_WAIT_QUEUE_HEAD(module_load_q);
-static DECLARE_WAIT_QUEUE_HEAD(module_unload_q);
+static DECLARE_WAIT_QUEUE_HEAD(module_wq);
 
 struct netfront_stats {
 	u64			packets;
@@ -1332,11 +1331,11 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
 	netif_carrier_off(netdev);
 
 	xenbus_switch_state(dev, XenbusStateInitialising);
-	wait_event(module_load_q,
-			   xenbus_read_driver_state(dev->otherend) !=
-			   XenbusStateClosed &&
-			   xenbus_read_driver_state(dev->otherend) !=
-			   XenbusStateUnknown);
+	wait_event(module_wq,
+		   xenbus_read_driver_state(dev->otherend) !=
+		   XenbusStateClosed &&
+		   xenbus_read_driver_state(dev->otherend) !=
+		   XenbusStateUnknown);
 	return netdev;
 
  exit:
@@ -2010,15 +2009,14 @@ static void netback_changed(struct xenbus_device *dev,
 
 	dev_dbg(&dev->dev, "%s\n", xenbus_strstate(backend_state));
 
+	wake_up_all(&module_wq);
+
 	switch (backend_state) {
 	case XenbusStateInitialising:
 	case XenbusStateInitialised:
 	case XenbusStateReconfiguring:
 	case XenbusStateReconfigured:
-		break;
-
 	case XenbusStateUnknown:
-		wake_up_all(&module_unload_q);
 		break;
 
 	case XenbusStateInitWait:
@@ -2034,12 +2032,10 @@ static void netback_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosed:
-		wake_up_all(&module_unload_q);
 		if (dev->state == XenbusStateClosed)
 			break;
 		/* Missed the backend's CLOSING state -- fallthrough */
 	case XenbusStateClosing:
-		wake_up_all(&module_unload_q);
 		xenbus_frontend_closed(dev);
 		break;
 	}
@@ -2147,14 +2143,14 @@ static int xennet_remove(struct xenbus_device *dev)
 
 	if (xenbus_read_driver_state(dev->otherend) != XenbusStateClosed) {
 		xenbus_switch_state(dev, XenbusStateClosing);
-		wait_event(module_unload_q,
+		wait_event(module_wq,
 			   xenbus_read_driver_state(dev->otherend) ==
 			   XenbusStateClosing ||
 			   xenbus_read_driver_state(dev->otherend) ==
 			   XenbusStateUnknown);
 
 		xenbus_switch_state(dev, XenbusStateClosed);
-		wait_event(module_unload_q,
+		wait_event(module_wq,
 			   xenbus_read_driver_state(dev->otherend) ==
 			   XenbusStateClosed ||
 			   xenbus_read_driver_state(dev->otherend) ==