drm/gem: Document that handle_create must be the last step
It published the gem object to userspace, by that point other threads
can guess the id and start using it. And gem IDs are _very_ easy to
guess (it's just an idr).
Since gem objects is the only thing we allow drivers to create
themselves (all the kms/prime/syncobj stuff is handled by the core) no
other functions seem to be in need of this clarification.
Motivated by reviewing the xen-front kms driver.
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180322080233.17266-1-daniel.vetter@ffwll.ch