[PATCH] drm/kms: Catch mode_object lifetime errors

[Daniel Vetter]

On Sat, Aug 17, 2019 at 12:42 AM Souza, Jose <jose.souza at intel.com> wrote:
> On Sat, 2019-06-29 at 17:39 +0200, Daniel Vetter wrote:
> > On Fri, Jun 28, 2019 at 7:24 PM Sean Paul <sean at poorly.run> wrote:
> > > On Fri, Jun 14, 2019 at 08:17:23AM +0200, Daniel Vetter wrote:
> > > > Only dynamic mode objects, i.e. those which are refcounted and
> > > > have a free
> > > > callback, can be added while the overall drm_device is visible to
> > > > userspace. All others must be added before drm_dev_register and
> > > > removed after drm_dev_unregister.
> > > >
> > > > Small issue around drivers still using the load/unload callbacks,
> > > > we
> > > > need to make sure we set dev->registered so that load/unload code
> > > > in
> > > > these callbacks doesn't trigger false warnings. Only a small
> > > > adjustement in drm_dev_register was needed.
> > > >
> > > > Motivated by some irc discussions about object ids of dynamic
> > > > objects
> > > > like blobs become invalid, and me going on a bit an audit spree.
> > > >
> > >
> > > Seems like a very worthwhile change, any idea how many drivers are
> > > going
> > > to be sad after this change?
> >
> > None I think/hope, really just defense WARN_ON just in case. The main
> > ones that would be sad are all the ones that have a ->load callback,
> > but I'm taking care of them. Everyone else does things correctly and
> > calls drm_dev_register last in their probe function (or around where
> > they set up fbdev, which is also register the driver at least to the
> > fbdev world, so really the same).
> >
> > > > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_drv.c         | 4 ++--
> > > >  drivers/gpu/drm/drm_mode_object.c | 4 ++++
> > > >  2 files changed, 6 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_drv.c
> > > > b/drivers/gpu/drm/drm_drv.c
> > > > index cb6f0245de7c..48c84e3e1931 100644
> > > > --- a/drivers/gpu/drm/drm_drv.c
> > > > +++ b/drivers/gpu/drm/drm_drv.c
> > > > @@ -997,14 +997,14 @@ int drm_dev_register(struct drm_device
> > > > *dev, unsigned long flags)
> > > >       if (ret)
> > > >               goto err_minors;
> > > >
> > > > -     dev->registered = true;
> > > > -
> > > >       if (dev->driver->load) {
> > > >               ret = dev->driver->load(dev, flags);
> > > >               if (ret)
> > > >                       goto err_minors;
> > > >       }
> > > >
> > > > +     dev->registered = true;
> > > > +
> > > >       if (drm_core_check_feature(dev, DRIVER_MODESET))
> > > >               drm_modeset_register_all(dev);
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_mode_object.c
> > > > b/drivers/gpu/drm/drm_mode_object.c
> > > > index 1c6e51135962..c355ba8e6d5d 100644
> > > > --- a/drivers/gpu/drm/drm_mode_object.c
> > > > +++ b/drivers/gpu/drm/drm_mode_object.c
> > > > @@ -42,6 +42,8 @@ int __drm_mode_object_add(struct drm_device
> > > > *dev, struct drm_mode_object *obj,
> > > >  {
> > > >       int ret;
> > > >
> > > > +     WARN_ON(dev->registered && !obj_free_cb);
>
> Getting warnings on i915 with MST, we add fake MST connectors when a
> sink with MST support is connected;
>
> intel_dp_add_mst_connector()->drm_connector_attach_max_bpc_property()
>
> Not sure how to fix that, add a global i915 device property like we do
> for "audio" and "Broadcast RGB" don't look the right approach here.
> Any tips?
>
> We definitely need a platform with a MST sink on our CI.

Uh yeah this is bad. I guess we need to preemptively create all
possible bpc properties, so that we can only do an attach. Those
really can't be hotplugged.

We might also want to revert

commit 5ca0ef8a56b8c4812ed78ef9ca53052191dab6e7
Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
Date:   Tue Mar 26 16:25:54 2019 +0200

    drm/i915: Add max_bpc property for DP MST

as an interim solution. Adding Ville and Jani.
-Daniel

> > >
> > > These should probably have a comment above them giving some
> > > guidance to the
> > > driver developer.
> > >
> > > With some comments, this is:
> >
> > What comment do you expect here? drm_dev_register explains what you
> > should do already, and I expect driver developers to find that one
> > pretty quickly. From there: "This should be done last in the device
> > initialization sequence to make sure userspace can't access an
> > inconsistent state."
> > -Daniel
> >
> > > Reviewed-by: Sean Paul <sean at poorly.run>
> > >
> > >
> > > > +
> > > >       mutex_lock(&dev->mode_config.idr_mutex);
> > > >       ret = idr_alloc(&dev->mode_config.object_idr, register_obj
> > > > ? obj : NULL,
> > > >                       1, 0, GFP_KERNEL);
> > > > @@ -102,6 +104,8 @@ void drm_mode_object_register(struct
> > > > drm_device *dev,
> > > >  void drm_mode_object_unregister(struct drm_device *dev,
> > > >                               struct drm_mode_object *object)
> > > >  {
> > > > +     WARN_ON(dev->registered && !object->free_cb);
> > > > +
> > > >       mutex_lock(&dev->mode_config.idr_mutex);
> > > >       if (object->id) {
> > > >               idr_remove(&dev->mode_config.object_idr, object-
> > > > >id);
> > > > --
> > > > 2.20.1
> > > >
> > > > _______________________________________________
> > > > dri-devel mailing list
> > > > dri-devel at lists.freedesktop.org
> > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> > >
> > > --
> > > Sean Paul, Software Engineer, Google / Chromium OS
> >
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch