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

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Message-ID: <5376489C.9010902@wwwdotorg.org>
Date:	Fri, 16 May 2014 11:19:24 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tejun Heo <tj@...nel.org>
CC:	lizefan@...wei.com, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	ARM kernel mailing list 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 cgroup/for-3.16] cgroup: introduce CSS_NO_REF and skip
 refcnting on normal root csses

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@...nel.org>
> Reported-by: Stephen Warren <swarren@...dotorg.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@...dia.com>
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