linux-kernel - Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle NULL state pointer

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Message-ID: <87edooarpq.fsf@intel.com>
Date:   Thu, 13 Apr 2023 15:31:45 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Jeff Layton <jlayton@...nel.org>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle
 NULL state pointer

On Thu, 13 Apr 2023, Jeff Layton <jlayton@...nel.org> wrote:
> 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.

My fear is that papering over this makes the root cause harder to find.

Cc: Harry, Alex


BR,
Jani.


>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2184855
> Signed-off-by: Jeff Layton <jlayton@...nel.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;
>  	}

-- 
Jani Nikula, Intel Open Source Graphics Center