tree db5e953a6b3e1d074e64c3e36e3b7c90fc564770
parent 25e15d835036a70a53dcc993beaa036f8919a373
author Tejun Heo <tj@kernel.org> 1400073302 -0400
committer Tejun Heo <tj@kernel.org> 1400073302 -0400

cgroup: enable refcnting for root csses

Currently, css_get(), css_tryget() and css_tryget_online() are noops
for root csses as an optimization; however, we're planning to use css
refcnts to track of cgroup lifetime too and root cgroups also need to
be reference counted.  Since css has been converted to percpu_refcnt,
the overhead of refcnting is miniscule and this optimization isn't too
meaningful anymore.  Furthermore, controllers which optimize the root
cgroup often never even invoke these functions in their hot paths.

This patch enables refcnting for root csses too.  This makes CSS_ROOT
flag unused and removes it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>