linux-kernel - Re: i865, drm_modeset_lock_all: BUG: unable to handle kernel NULL pointer dereference at 00000104

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Date:   Tue, 23 Aug 2016 11:10:54 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Meelis Roos <mroos@...ux.ee>
Cc:     Linux Kernel list <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org
Subject: Re: i865, drm_modeset_lock_all: BUG: unable to handle kernel NULL
 pointer dereference at 00000104

On Tue, Aug 23, 2016 at 02:35:03PM +0300, Meelis Roos wrote:
> > Looks like an incorrect call to drm_encoder_cleanup() from the error
> > path. If we hit the error path we have never called drm_encoder_init.
> > Please try:
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dvo.c b/drivers/gpu/drm/i915/intel_dvo.c
> > index 47bdf9dad0d3..b9e5a63a7c9e 100644
> > --- a/drivers/gpu/drm/i915/intel_dvo.c
> > +++ b/drivers/gpu/drm/i915/intel_dvo.c
> > @@ -554,7 +554,6 @@ void intel_dvo_init(struct drm_device *dev)
> >  		return;
> >  	}
> >  
> > -	drm_encoder_cleanup(&intel_encoder->base);
> >  	kfree(intel_dvo);
> >  	kfree(intel_connector);
> >  }
> 
> It works - the BUG is gone.
> 
> Now I get just 
> [drm:__intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR* pipe A underrun

Other than the annoying underrun, is everything else as expected? i.e.
no connected outputs? Have we lost dvo detection?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre