[PATCH 02/13] vfio/mdev: embedd struct mdev_parent in the parent data structure

[Jason Gunthorpe]

On Fri, Jun 24, 2022 at 05:59:58PM +0530, Kirti Wankhede wrote:

> > The reason this is here is because the type->parent is used in a few
> > places and is put back in release:
> > 
> > @@ -81,7 +81,7 @@ static void mdev_type_release(struct kobject *kobj)
> > 
> >          pr_debug("Releasing group %s\n", kobj->name);
> >          /* Pairs with the get in add_mdev_supported_type() */
> > -       mdev_put_parent(type->parent);
> > +       put_device(type->parent->dev);
> >          kfree(type);
> >   }
> > 
> > If this was a simple sysfs kobj with only a show/store we wouldn't
> > need to do anything as the natural kobj parentage holds a ref up to
> > the struct device - but this kobj is used internally, ie dependent
> > from mdev_device_create(), independently of the normal sysfs
> > life-cycle so that doesn't protect enough either.
> > 
> 
> 
> Life span of 'type' is from mdev_register_device to mdev_unregister_device.
> If device/parent is being unregistered then only types are removed, so
> referencing 'type' from mdev_device_create() is still safe. Therefore,
> parent device's reference should be held and release from
> register-unregister call.

No, I've already explained this.

Jason