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

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Date:   Tue, 20 Jun 2023 15:50:24 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Jeff Layton <jlayton@...nel.org>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Wayne.Lin@....com, alexdeucher@...il.com,
        Jani Nikula <jani.nikula@...ux.intel.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

Eek - this might have been a situation where everyone involved assumed someone
else would push it, whoops. I'll make sure this is pushed upstream :).

FWIW: You could definitely send an MR to the fedora kernel's gitlab to get
this included earlier. If you don't get to it before me I'll try to do that
today

On Tue, 2023-06-20 at 07:18 -0400, Jeff Layton wrote:
> I've noticed that this patch is not included in linux-next currently.
> 
> Can I get some confirmation that this is going to be included in v6.5?
> Currently, I've been having to rebuild Fedora kernels to avoid this
> panic, and I'd like to know there is a light at the end of that tunnel.
> 
> Thanks,
> Jeff
> 
> On Wed, 2023-04-19 at 16:54 -0400, Lyude Paul wrote:
> > Reviewed-by: Lyude Paul <lyude@...hat.com>
> > 
> > Thanks!
> > 
> > On Wed, 2023-04-19 at 07:24 -0400, Jeff Layton 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>
> > > ---
> > >  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;
> > >  	}
> > 
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat