Pull cgroup fix from Tejun Heo:
"cgroup.threads should be delegatable (ie. a container should be able
to write to it from inside) but was missing the flag.
The change is very low risk"
* 'for-4.15-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: make cgroup.threads delegatable