[PATCH 22/52] drm: Use drmm_ for drm_dev_init cleanup

[Daniel Vetter]

On Wed, Feb 19, 2020 at 3:35 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Daniel,
>
> Thank you for the patch.
>
> On Wed, Feb 19, 2020 at 11:20:52AM +0100, Daniel Vetter wrote:
> > Well for the simple stuff at least, vblank, gem and minor cleanup I
> > want to further split up as a demonstration.
> >
> > v2: We need to clear drm_device->dev otherwise the debug drm printing
> > after our cleanup hook (e.g. in drm_manged_release) will chase
> > released memory and result in a use-after-free. Not really pretty, but
> > oh well.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  drivers/gpu/drm/drm_drv.c | 48 ++++++++++++++++++++-------------------
> >  1 file changed, 25 insertions(+), 23 deletions(-)
>
> Is the managed API overhead, coupled with the fact that the code size
> doesn't get reduced, worth it for core code ?

I've mostly done this as an example, to show how if you do this
consistently, you can drop a few if (is_it_set_up) checks and remove
the onion unwinding with lots of gotos. I do think it's worth it from
that pov, since long-term I want to get to a world where everything
related to drm_device gets unwound with drmm_ actions. The logging
output becomes fairly nice if you enable it :-)

But yeah stand-alone it's not a good pitch. Heck even the overall
patch series is still a net loss I think, simply because this is just
the bare minimum to get started.
-Daniel

> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index 782fd5d6f8b2..1f7ab88d9435 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -580,6 +580,23 @@ static void drm_fs_inode_free(struct inode *inode)
> >   *    used.
> >   */
> >
> > +static void drm_dev_init_release(struct drm_device *dev, void *res)
> > +{
> > +     drm_legacy_ctxbitmap_cleanup(dev);
> > +     drm_legacy_remove_map_hash(dev);
> > +     drm_fs_inode_free(dev->anon_inode);
> > +
> > +     put_device(dev->dev);
> > +     /* Prevent use-after-free in drm_managed_release when debugging is
> > +      * enabled. Slightly awkward, but can't really be helped. */
> > +     dev->dev = NULL;
> > +     mutex_destroy(&dev->master_mutex);
> > +     mutex_destroy(&dev->clientlist_mutex);
> > +     mutex_destroy(&dev->filelist_mutex);
> > +     mutex_destroy(&dev->struct_mutex);
> > +     drm_legacy_destroy_members(dev);
> > +}
> > +
> >  /**
> >   * drm_dev_init - Initialise new DRM device
> >   * @dev: DRM device
> > @@ -647,11 +664,15 @@ int drm_dev_init(struct drm_device *dev,
> >       mutex_init(&dev->clientlist_mutex);
> >       mutex_init(&dev->master_mutex);
> >
> > +     ret = drmm_add_action(dev, drm_dev_init_release, NULL);
> > +     if (ret)
> > +             return ret;
> > +
> >       dev->anon_inode = drm_fs_inode_new();
> >       if (IS_ERR(dev->anon_inode)) {
> >               ret = PTR_ERR(dev->anon_inode);
> >               DRM_ERROR("Cannot allocate anonymous inode: %d\n", ret);
> > -             goto err_free;
> > +             goto err;
> >       }
> >
> >       if (drm_core_check_feature(dev, DRIVER_RENDER)) {
> > @@ -688,19 +709,12 @@ int drm_dev_init(struct drm_device *dev,
> >       if (drm_core_check_feature(dev, DRIVER_GEM))
> >               drm_gem_destroy(dev);
> >  err_ctxbitmap:
> > -     drm_legacy_ctxbitmap_cleanup(dev);
> > -     drm_legacy_remove_map_hash(dev);
> >  err_minors:
> >       drm_minor_free(dev, DRM_MINOR_PRIMARY);
> >       drm_minor_free(dev, DRM_MINOR_RENDER);
> > -     drm_fs_inode_free(dev->anon_inode);
> > -err_free:
> > -     put_device(dev->dev);
> > -     mutex_destroy(&dev->master_mutex);
> > -     mutex_destroy(&dev->clientlist_mutex);
> > -     mutex_destroy(&dev->filelist_mutex);
> > -     mutex_destroy(&dev->struct_mutex);
> > -     drm_legacy_destroy_members(dev);
> > +err:
> > +     drm_managed_release(dev);
> > +
> >       return ret;
> >  }
> >  EXPORT_SYMBOL(drm_dev_init);
> > @@ -763,20 +777,8 @@ void drm_dev_fini(struct drm_device *dev)
> >       if (drm_core_check_feature(dev, DRIVER_GEM))
> >               drm_gem_destroy(dev);
> >
> > -     drm_legacy_ctxbitmap_cleanup(dev);
> > -     drm_legacy_remove_map_hash(dev);
> > -     drm_fs_inode_free(dev->anon_inode);
> > -
> >       drm_minor_free(dev, DRM_MINOR_PRIMARY);
> >       drm_minor_free(dev, DRM_MINOR_RENDER);
> > -
> > -     put_device(dev->dev);
> > -
> > -     mutex_destroy(&dev->master_mutex);
> > -     mutex_destroy(&dev->clientlist_mutex);
> > -     mutex_destroy(&dev->filelist_mutex);
> > -     mutex_destroy(&dev->struct_mutex);
> > -     drm_legacy_destroy_members(dev);
> >  }
> >  EXPORT_SYMBOL(drm_dev_fini);
> >
>
> --
> Regards,
>
> Laurent Pinchart



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