Re: [PATCH] drm/atomic: Clean old_state/new_state in drm_atomic_state_default_clear()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, May 03, 2018 at 08:35:30AM +0200, Daniel Vetter wrote:
> On Wed, May 02, 2018 at 09:32:47PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Clear the old_state and new_state pointers for every object in
> > drm_atomic_state_default_clear(). Otherwise
> > drm_atomic_get_{new,old}_*_state() will hand out stale pointers to
> > anyone who hasn't first confirmed that the object is in fact part of
> > the current atomic transcation, if they are called after we've done
> > the ww backoff dance while hanging on to the same drm_atomic_state.
> > 
> > For example, handle_conflicting_encoders() looks like it could hit
> > this since it iterates the full connector list and just calls
> > drm_atomic_get_new_connector_state() for each.
> > 
> > And I believe we have now witnessed this happening at least once in
> > i915 check_digital_port_conflicts(). Commit 8b69449d2663 ("drm/i915:
> > Remove last references to drm_atomic_get_existing* macros") changed
> > the safe drm_atomic_get_existing_connector_state() to the unsafe
> > drm_atomic_get_new_connector_state(), which opened the doors for
> > this particular bug there as well.
> > 
> > Cc: stable@vger.kernel.org
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Cc: Abhay Kumar <abhay.kumar@intel.com>
> > Fixes: 581e49fe6b41 ("drm/atomic: Add new iterators over all state, v3.")
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Uh ... that's some bad oversight :-/
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> btw for stable we might want to split this into 1 patch for core objects
> and 1 patch for driver private stuff.

Good point. I forgot we did that after the new iterators were
introduced. I'll do the split.

> Feel free to do so while applying
> and keep my r-b. The fixes line for the 2nd patch would be:
> 
> Fixes: a4370c777406 ("drm/atomic: Make private objs proper objects")
> Cc: <stable@vger.kernel.org> # v4.14+

Ta.

> 
> Cheers, Daniel
> > ---
> >  drivers/gpu/drm/drm_atomic.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 7d25c42f22db..c825c76edc1d 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -155,6 +155,8 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> >  						       state->connectors[i].state);
> >  		state->connectors[i].ptr = NULL;
> >  		state->connectors[i].state = NULL;
> > +		state->connectors[i].old_state = NULL;
> > +		state->connectors[i].new_state = NULL;
> >  		drm_connector_put(connector);
> >  	}
> >  
> > @@ -169,6 +171,8 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> >  
> >  		state->crtcs[i].ptr = NULL;
> >  		state->crtcs[i].state = NULL;
> > +		state->crtcs[i].old_state = NULL;
> > +		state->crtcs[i].new_state = NULL;
> >  	}
> >  
> >  	for (i = 0; i < config->num_total_plane; i++) {
> > @@ -181,6 +185,8 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> >  						   state->planes[i].state);
> >  		state->planes[i].ptr = NULL;
> >  		state->planes[i].state = NULL;
> > +		state->planes[i].old_state = NULL;
> > +		state->planes[i].new_state = NULL;
> >  	}
> >  
> >  	for (i = 0; i < state->num_private_objs; i++) {
> > @@ -190,6 +196,8 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> >  						 state->private_objs[i].state);
> >  		state->private_objs[i].ptr = NULL;
> >  		state->private_objs[i].state = NULL;
> > +		state->private_objs[i].old_state = NULL;
> > +		state->private_objs[i].new_state = NULL;
> >  	}
> >  	state->num_private_objs = 0;
> >  
> > -- 
> > 2.16.1
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel
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