[PATCH v2 cgroup/for-3.16] cgroup: introduce CSS_NO_REF and skip refcnting on normal root csses

[Stephen Warren]

On 05/16/2014 11:09 AM, Tejun Heo wrote:
> 9395a4500404 ("cgroup: enable refcnting for root csses") enabled
> reference counting for root csses (cgroup_subsys_states) so that
> cgroup's self csses can be used to manage the lifetime of the
> containing cgroups.
> 
> Unfortunately, this change was incorrect.  During early init,
> cgrp_dfl_root self css refcnt is used.  percpu_ref can't initialized
> during early init and its initialization is deferred till
> cgroup_init() time.  This means that cpu was using percpu_ref which
> wasn't properly initialized.  Due to the way percpu variables are laid
> out on x86, this didn't blow up immediately on x86 but ended up
> incrementing and decrementing the percpu variable at offset zero,
> whatever it may be; however, on other archs, this caused fault and
> early boot failure.
> 
> As cgroup self csses for root cgroups of non-dfl hierarchies need
> working refcounting, we can't revert 9395a4500404.  This patch adds
> CSS_NO_REF which explicitly inhibits reference counting on the css and
> sets it on all normal (non-self) csses and cgroup_dfl_root self css.
> 
> v2: cgrp_dfl_root.self is the offending one.  Set the flag on it.
> 
> Signed-off-by: Tejun Heo <tj at kernel.org>
> Reported-by: Stephen Warren <swarren at wwwdotorg.org>
> Fixes: 9395a4500404 ("cgroup: enable refcnting for root csses")
> ---
> Hello,
> 
> Can you try this one instead?

Yes, this one works great, thanks.
Tested-by: Stephen Warren <swarren at nvidia.com>