linux-kernel - Re: [PATCH 2/2] drm/atomic: clear new_state pointers at hw

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Date:   Fri, 1 Nov 2019 12:49:02 -0700
From:   Rob Clark <robdclark@...omium.org>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Rob Clark <robdclark@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        Sean Paul <seanpaul@...omium.org>, Sean Paul <sean@...rly.run>
Subject: Re: [PATCH 2/2] drm/atomic: clear new_state pointers at hw_done

On Fri, Nov 1, 2019 at 12:25 PM Ville Syrjälä
<ville.syrjala@...ux.intel.com> wrote:
>
> On Fri, Nov 01, 2019 at 11:07:13AM -0700, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > The new state should not be accessed after this point.  Clear the
> > pointers to make that explicit.
> >
> > This makes the error corrected in the previous patch more obvious.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 732bd0ce9241..176831df8163 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -2234,13 +2234,42 @@ EXPORT_SYMBOL(drm_atomic_helper_fake_vblank);
> >   */
> >  void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
> >  {
> > +     struct drm_connector *connector;
> > +     struct drm_connector_state *old_conn_state, *new_conn_state;
> >       struct drm_crtc *crtc;
> >       struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> > +     struct drm_plane *plane;
> > +     struct drm_plane_state *old_plane_state, *new_plane_state;
> >       struct drm_crtc_commit *commit;
> > +     struct drm_private_obj *obj;
> > +     struct drm_private_state *old_obj_state, *new_obj_state;
> >       int i;
> >
> > +     /*
> > +      * After this point, drivers should not access the permanent modeset
> > +      * state, so we also clear the new_state pointers to make this
> > +      * restriction explicit.
> > +      *
> > +      * For the CRTC state, we do this in the same loop where we signal
> > +      * hw_done, since we still need to new_crtc_state to fish out the
> > +      * commit.
> > +      */
> > +
> > +     for_each_oldnew_connector_in_state(old_state, connector, old_conn_state, new_conn_state, i) {
> > +             old_state->connectors[i].new_state = NULL;
> > +     }
> > +
> > +     for_each_oldnew_plane_in_state(old_state, plane, old_plane_state, new_plane_state, i) {
> > +             old_state->planes[i].new_state = NULL;
> > +     }
> > +
> > +     for_each_oldnew_private_obj_in_state(old_state, obj, old_obj_state, new_obj_state, i) {
> > +             old_state->private_objs[i].new_state = NULL;
> > +     }
> > +
> >       for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
> >               old_state->crtcs[i].new_self_refresh_active = new_crtc_state->self_refresh_active;
> > +             old_state->crtcs[i].new_state = NULL;
>
> That's going to be a real PITA when doing programming after the fact from
> a vblank worker. It's already a pain that the new_crtc_state->state is
> getting NULLed somewhere.
>

I think you already have that problem, this just makes it explicit.

BR,
-R