linux-kernel - Re: [PATCH v1] drm/dp/mst: fix missing modeset unlock for MST port detect

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Date:   Fri, 22 Sep 2023 22:22:21 +0300
From:   Imre Deak <imre.deak@...el.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     Ramya SR <quic_rsr@...cinc.com>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Wayne Lin <Wayne.Lin@....com>,
        Jani Nikula <jani.nikula@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Jeff Layton <jlayton@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm/dp/mst: fix missing modeset unlock for MST port
 detect

On Fri, Sep 22, 2023 at 03:02:23PM -0400, Lyude Paul wrote:
> 
> Oh! wow thank you for catching this:
> 
> Reviewed-by: Lyude Paul <lyude@...hat.com>
> 
> I will go and push this to drm-misc-next in just a moment
> 
> On Fri, 2023-09-15 at 10:24 +0530, Ramya SR wrote:
> > Modeset mutex unlock is missing in drm_dp_mst_detect_port function.
> > This will lead to deadlock if calling the function multiple times in
> > an atomic operation, for example, getting imultiple MST ports status
> > for a DP MST bonding scenario.
> > 
> > Signed-off-by: Ramya SR <quic_rsr@...cinc.com>
> > ---
> >  drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++-
> >  1 file changed, 3 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 ed96cfc..d6512c4 100644
> > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > @@ -4154,7 +4154,7 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
> >  
> >  	ret = drm_modeset_lock(&mgr->base.lock, ctx);
> >  	if (ret)
> > -		goto out;
> > +		goto fail;
> >  
> >  	ret = connector_status_disconnected;
> >  
> > @@ -4181,6 +4181,8 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
> >  		break;
> >  	}
> >  out:
> > +	drm_modeset_unlock(&mgr->base.lock);

Isn't this supposed to be unlocked only by drm_helper_probe_detect_ctx()
/ drm_helper_probe_detect() ?

> > +fail:
> >  	drm_dp_mst_topology_put_port(port);
> >  	return ret;
> >  }
> 
> -- 
> Cheers,
>  Lyude Paul (she/her)
>  Software Engineer at Red Hat
>