linux-kernel - [PATCH] drm/radeon: Fix kernel panic on shutdown

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Date:   Sun, 30 Oct 2016 23:40:53 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, driver-devel@...r.kernel.org,
        Larry Finger <Larry.Finger@...inger.net>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH] drm/radeon: Fix kernel panic on shutdown

Since commit a481daa88fd4 ("drm/radeon: always apply pci shutdown
callbacks"), a Dell Latitude D600 laptop has crashed on shutdown. The
PCI Identification of the graphics adapter is "VGA compatible controller
[0300]: Advanced Micro Devices, Inc. [AMD/ATI] RV250/M9 GL [Mobility
FireGL 9000/Radeon 9000] [1002:4c66] (rev 01)".

Prior to commit b0c80bd5d2e3 ("drm/radeon: fix up dp aux tear down (v2)"),
I have no idea where the panic happened as the screen was blanked before
the crash.  Since that more recent change, the panic has been in routine
radeon_connector_unregister(), and has been shown to be due to a NULL
value in the ddc_bus member of struct drm_connector.

Fixes: a481daa88fd4 ("drm/radeon: always apply pci shutdown callbacks")
Signed-off-by: Larry Finger <Larry.Finger@...inger.net>
Cc: Alex Deucher <alexander.deucher@....com>
---
 drivers/gpu/drm/radeon/radeon_connectors.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index e18839d..27affbd 100644
--- 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;
 	}
-- 
2.10.0