this is a wild race condition, but it's possible for these to get their
final unref, enter their destructor, and then get a cache hit while waiting
on the lock to remove themselves from the cache
in such a scenario, a second, normal check of the refcount will suffice,
as the increment is atomic, and the value will otherwise be zero
fixes crashes in basemark
cc: mesa-stable
Reviewed-by: Hoe Hao Cheng <haochengho12907@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13442>
86b3d8c66c