cgroup: use cgroup->self.refcnt for cgroup refcnting
Currently cgroup implements refcnting separately using atomic_t
cgroup->refcnt. The destruction paths of cgroup and css are rather
complex and bear a lot of similiarities including the use of RCU and
bouncing to a work item.
This patch makes cgroup use the refcnt of self css for refcnting
instead of using its own. This makes cgroup refcnting use css's
percpu refcnt and share the destruction mechanism.
* css_release_work_fn() and css_free_work_fn() are updated to handle
both csses and cgroups. This is a bit messy but should do until we
can make cgroup->self a full css, which currently can't be done
thanks to multiple hierarchies.
* cgroup_destroy_locked() now performs
percpu_ref_kill(&cgrp->self.refcnt) instead of cgroup_put(cgrp).
* Negative refcnt sanity check in cgroup_get() is no longer necessary
as percpu_ref already handles it.
* Similarly, as a cgroup which hasn't been killed will never be
released regardless of its refcnt value and percpu_ref has sanity
check on kill, cgroup_is_dead() sanity check in cgroup_put() is no
longer necessary.
* As whether a refcnt reached zero or not can only be decided after
the reference count is killed, cgroup_root->cgrp's refcnting can no
longer be used to decide whether to kill the root or not. Let's
make cgroup_kill_sb() explicitly initiate destruction if the root
doesn't have any children. This makes sense anyway as unmounted
cgroup hierarchy without any children should be destroyed.
While this is a bit messy, this will allow pushing more bookkeeping
towards cgroup->self and thus handling cgroups and csses in more
uniform way. In the very long term, it should be possible to
introduce a base subsystem and convert the self css to a proper one
making things whole lot simpler and unified.
Signed-off-by: Tejun Heo <tj@kernel.org>
2 files changed
