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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Daniel,

On Wed, Feb 19, 2020 at 04:27:57PM +0100, Daniel Vetter wrote:
> On Wed, Feb 19, 2020 at 3:35 PM Laurent Pinchart wrote:
> > 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@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.

That's however more a matter of making the cleanup handlers idempotent
than using a managed API, isn't it ?

> 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
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