Pull workqueue updates from Tejun Heo:
 "rcu_work addition and a couple trivial changes"

* 'for-4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: remove the comment about the old manager_arb mutex
  workqueue: fix the comments of nr_idle
  fs/aio: Use rcu_work instead of explicit rcu and work item
  cgroup: Use rcu_work instead of explicit rcu and work item
  RCU, workqueue: Implement rcu_work