[PATCH] drm/gem: use new idr deletion interface to cleanup drm_gem_handle_delete()

[Chris Wilson]

Quoting Aishwarya Pant (2017-09-25 19:47:28)
> The IDR deletion interface now returns the deleted entry or NULL if it was not
> present. So we don't have to do the extra work of checking if we have a
> reference on the drm_gem_object, this can be handled by checking the return
> value from idr_remove() and the extra locks can be dropped.
> 
> Signed-off-by: Aishwarya Pant <aishpant at gmail.com>

This reintroduces the bug were the idr entry is available for reuse
before the drivers have had the change to release their resources. So a
new handle may be reused that is then hooked up to the old private data.
See commit f6cd7daecff558fab2c45d15283d3e52f688342d
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Apr 15 12:55:08 2016 +0100

    drm: Release driver references to handle before making it available again
-Chris