Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4

[Larry Finger]

With the 4.9-rcX kernel, my Dell Latitude D600 laptop has a kernel panic on 
shutdown in routine radeon_connector_unregister(). This problem has been 
bisected to show that commit a481daa88fd4 ("drm/radeon: always apply pci 
shutdown callbacks") is at fault.

In the routine that crashes, the ddc_bus member of the struct drm_connector is 
NULL, thus the following one-line (line-wrapped) patch fixes the problem:

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c 
b/drivers/gpu/drm/radeon/radeon_connectors.c
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -931,7 +931,7 @@ static void radeon_connector_unregister(struct drm_connector 
*connector)
 {
        struct radeon_connector *radeon_connector = to_radeon_connector(connector);

-       if (radeon_connector->ddc_bus->has_aux) {
+       if (radeon_connector->ddc_bus && radeon_connector->ddc_bus->has_aux) {
                drm_dp_aux_unregister(&radeon_connector->ddc_bus->aux);
                radeon_connector->ddc_bus->has_aux = false;
        }

The above change will soon be submitted as a proper patch. This posting to LKML 
is intended to publicize the regression as soon as possible.

Larry