linux-kernel - [PATCH v2] drm: use mgr->dev in drm_dbg_kms in drm_dp_add_payload

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Date:   Wed, 19 Apr 2023 07:24:46 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc:     Wayne.Lin@....com, lyude@...hat.com, alexdeucher@...il.com,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] drm: use mgr->dev in drm_dbg_kms in drm_dp_add_payload_part2

I've been experiencing some intermittent crashes down in the display
driver code. The symptoms are ususally a line like this in dmesg:

    amdgpu 0000:30:00.0: [drm] Failed to create MST payload for port 000000006d3a3885: -5

...followed by an Oops due to a NULL pointer dereference.

Switch to using mgr->dev instead of state->dev since "state" can be
NULL in some cases.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2184855
Suggested-by: Jani Nikula <jani.nikula@...ux.intel.com>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

I've been running this patch for a couple of days, but the problem
hasn't occurred again as of yet. It seems sane though as long as we can
assume that mgr->dev will be valid even when "state" is a NULL pointer.

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 38dab76ae69e..e2e21ce79510 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3404,7 +3404,7 @@ int drm_dp_add_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
 
 	/* Skip failed payloads */
 	if (payload->vc_start_slot == -1) {
-		drm_dbg_kms(state->dev, "Part 1 of payload creation for %s failed, skipping part 2\n",
+		drm_dbg_kms(mgr->dev, "Part 1 of payload creation for %s failed, skipping part 2\n",
 			    payload->port->connector->name);
 		return -EIO;
 	}
-- 
2.39.2