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

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Message-ID: <87o7nkypmo.fsf@intel.com>
Date:   Wed, 19 Apr 2023 16:21:03 +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:     Wayne.Lin@....com, lyude@...hat.com, alexdeucher@...il.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: use mgr->dev in drm_dbg_kms in
 drm_dp_add_payload_part2

On Wed, 19 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.
>
> 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>

Thanks,

Reviewed-by: Jani Nikula <jani.nikula@...el.com>


> ---
>  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;
>  	}

-- 
Jani Nikula, Intel Open Source Graphics Center