This regression has been introduced in
commit 
b3f2333de8e81b089262b26d52272911523e605f
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Dec 11 11:34:31 2013 +0100
    drm: restrict the device list for shadow attached drivers
Reported-by: Dave Jones <davej@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
        } else {
                list_for_each_entry_safe(dev, tmp, &driver->legacy_dev_list,
                                         legacy_dev_list) {
-                       drm_put_dev(dev);
                        list_del(&dev->legacy_dev_list);
+                       drm_put_dev(dev);
                }
        }
        DRM_INFO("Module unloaded\n");