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Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4

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  Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4 Larry Finger <Larry.Finger@lwfinger.net> - 2016-10-31 00:40 +0100
    Re: Regression in kernel 4.9-rcX - bisected to commit a481daa88fd4 Thorsten Leemhuis <regressions@leemhuis.info> - 2016-11-06 12:30 +0100

#1512237 — 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

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#1515674

On 31.10.2016 00:32, Larry Finger wrote:
> 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:
> […]
> 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.

JFYI: I added this report to the list of regressions for Linux 4.9. I'll
watch this thread for further updates on this issue to document progress
in my weekly reports. Please let me know via regressions@leemhuis.info
in case the discussion moves to a different place (bugzilla or another
mail thread for example).

Current status (afaics): Patch available

tia! Ciao, Thorsten

P.S.: Thx for CCing me!

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