linux-kernel - Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4

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Date:   Sun, 30 Oct 2016 18:32:41 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     LKML <linux-kernel@...r.kernel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Alex Deucher <alexander.deucher@....com>
Subject: Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4

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