xen-netback: stop the VIF thread before unbinding IRQs

If the VIF thread is still running after unbinding the Tx and Rx IRQs
in xenvif_disconnect(), the thread may attempt to raise an event which
will BUG (as the irq is unbound).
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/interface.c

@@ -461,6 +461,9 @@ void xenvif_disconnect(struct xenvif *vif)
 	if (netif_carrier_ok(vif->dev))
 		xenvif_carrier_off(vif);
 
+	if (vif->task)
+		kthread_stop(vif->task);
+
 	if (vif->tx_irq) {
 		if (vif->tx_irq == vif->rx_irq)
 			unbind_from_irqhandler(vif->tx_irq, vif);
@@ -471,9 +474,6 @@ void xenvif_disconnect(struct xenvif *vif)
 		vif->tx_irq = 0;
 	}
 
-	if (vif->task)
-		kthread_stop(vif->task);
-
 	xenvif_unmap_frontend_rings(vif);
 }