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

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Date:   Thu, 13 Apr 2023 08:58:32 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Wayne Lin <Wayne.Lin@....com>
Cc:     Jeff Layton <jlayton@...nel.org>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Alex Deucher <alexander.deucher@....com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle NULL
 state pointer

+ Wayne

On Thu, Apr 13, 2023 at 8:31 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>
> 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