linux-kernel - Re: [PATCH] cgroup: Check task_lock in task_subsys

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Date:	Thu, 22 Apr 2010 21:10:03 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Lai JIangshan <laijs@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Cedric Le Goater <clg@...t.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"containers@...ts.osdl.org" <containers@...ts.osdl.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] cgroup: Check task_lock in task_subsys_state()

On Fri, Apr 23, 2010 at 10:35:52AM +0800, Li Zefan wrote:
> task_subsys_state() is safe under task_lock(). See
> Documentation/cgroups/cgroups.txt for locking rule.
> 
> This fixes an RCU warning when resume from suspend. The
> warning comes from freezer cgroup in cgroup_freezing_or_frozen().
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
> 
> I'm not sure which is preferable - access ->alloc_lock directly
> like this patch or add task_lock_is_held() in sched.h

This is for the maintainers to decide, either way works from my viewpoint.

I have queued it as is with Matt's Acked-by, and am testing it.  Thank you!!!

							Thanx, Paul

> ---
>  include/linux/cgroup.h |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index b8ad1ea..8f78073 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -530,6 +530,7 @@ static inline struct cgroup_subsys_state *task_subsys_state(
>  {
>  	return rcu_dereference_check(task->cgroups->subsys[subsys_id],
>  				     rcu_read_lock_held() ||
> +				     lockdep_is_held(&task->alloc_lock) ||
>  				     cgroup_lock_is_held());
>  }
> 
> -- 
> 1.6.3
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