[PATCH] drm/kms: Catch mode_object lifetime errors

[Souza, Jose]

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.

> > 
> > 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
> 
>