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Message-ID: <cc3ceecef10fabf6856e29c2dd22b040b3ea757b.camel@kernel.org>
Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle
 NULL state pointer
From:   Jeff Layton <jlayton@kernel.org>
To:     Jani Nikula <jani.nikula@linux.intel.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Harry Wentland <harry.wentland@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>
Date:   Thu, 13 Apr 2023 08:43:52 -0400
In-Reply-To: <87edooarpq.fsf@intel.com>
References: <20230413111254.22458-1-jlayton@kernel.org>
         <87edooarpq.fsf@intel.com>
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On Thu, 2023-04-13 at 15:31 +0300, Jani Nikula wrote:
> On Thu, 13 Apr 2023, Jeff Layton <jlayton@kernel.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:
> >=20
> >     amdgpu 0000:30:00.0: [drm] Failed to create MST payload for port 00=
0000006d3a3885: -5
> >=20
> > ...followed by an Oops due to a NULL pointer dereference.
> >=20
> > 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.
>=20
> My fear is that papering over this makes the root cause harder to find.
>=20
> Cc: Harry, Alex
>=20
>=20
> BR,
> Jani.
>=20
>=20

I'm happy to help track down the root cause. Display drivers are
somewhat outside my wheelhouse though.

Maybe we can throw a WARNING when this happens? I'd just like it to not
crash my machine.


> >=20
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=3D2184855
> > 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(-)
> >=20
> > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gp=
u/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_to=
pology_mgr *mgr,
> > =20
> >  	/* Skip failed payloads */
> >  	if (payload->vc_start_slot =3D=3D -1) {
> > -		drm_dbg_kms(state->dev, "Part 1 of payload creation for %s failed, s=
kipping 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;
> >  	}
>=20

--=20
Jeff Layton <jlayton@kernel.org>