linux-kernel - Re: [PATCH 9/9] cgroup: use cgroup->self.refcnt for cgroup refcnting

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Message-ID: <53751062.2050401@wwwdotorg.org>
Date:	Thu, 15 May 2014 13:07:14 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tejun Heo <tj@...nel.org>, lizefan@...wei.com
CC:	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 9/9] cgroup: use cgroup->self.refcnt for cgroup refcnting

On 05/09/2014 03:13 PM, Tejun Heo wrote:
> 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.
>...

In next-20150515, this patch causes silent boot failures on NVIDIA Tegra
ARM systems. There isn't even any earlyprintk. Reverting this one patch
solves this.

I was a bit surprised that cgroups would cause such an issue, but
looking at a normal kernel boot, I guess cgroup does get initialized
very early:

Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacct

Anyway, I'll try to track down what the problem is, but if someone
familiar with this patch could give it a look, that'd be very useful,
since I'm not at all familiar with this code or feature.
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