On 05/16/2014 09:43 AM, Tejun Heo wrote:
> From 49035d695d8f1c4bbe4e37480e5d06812818947c Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@xxxxxxxxxx>
> Date: Fri, 16 May 2014 11:40:33 -0400
>
> 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. cpu controller uses
> early_init and starts using css reference counts on its root css from
> then on. 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 still 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.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Reported-by: Stephen Warren <swarren@xxxxxxxxxxxxx>
> Fixes: 9395a4500404 ("cgroup: enable refcnting for root csses")
> ---
> Patch applied to cgroup/for-3.16.
Unfortunately, this patch doesn't seem to solve the problem for me. I
still get a hang/crash very early during boot, before earlyprintk stars.
I tried this patch on top of both next-20150115, and next-20150516. For
both those kernels, reverting the original problematic patch does
resolve the problem.
I'll try to investigate more later today.
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