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From:   Jeff Layton <jlayton@kernel.org>
To:     David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle NULL state pointer
Date:   Thu, 13 Apr 2023 07:12:54 -0400
Message-Id: <20230413111254.22458-1-jlayton@kernel.org>
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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.

The real bug is probably in the caller of this function, which is
passing it a NULL state pointer, but this patch at least keeps my
machine from oopsing when this occurs.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2184855
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 38dab76ae69e..87ad406c50f9 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3404,7 +3404,8 @@ 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(state ? state->dev : NULL,
+			    "Part 1 of payload creation for %s failed, skipping part 2\n",
 			    payload->port->connector->name);
 		return -EIO;
 	}
-- 
2.39.2