linux-kernel - Re: [PATCH 17/24] blkcg: implement blkcg_policy->on/offline_pd_fn() and blkcg

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Message-ID: <20130102203718.GE11220@mtj.dyndns.org>
Date:	Wed, 2 Jan 2013 15:37:18 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	lizefan@...wei.com, axboe@...nel.dk,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, ctalbott@...gle.com, rni@...gle.com
Subject: Re: [PATCH 17/24] blkcg: implement blkcg_policy->on/offline_pd_fn()
 and blkcg_gq->online

On Wed, Jan 02, 2013 at 02:38:28PM -0500, Vivek Goyal wrote:
> On Fri, Dec 28, 2012 at 12:35:39PM -0800, Tejun Heo wrote:
> 
> [..]
> > diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
> > index 40f5b97..678e89e 100644
> > --- a/block/blk-cgroup.h
> > +++ b/block/blk-cgroup.h
> > @@ -106,12 +106,17 @@ struct blkcg_gq {
> >  	/* reference count */
> >  	int				refcnt;
> >  
> > +	/* is this blkg online? protected by both blkcg and q locks */
> > +	bool				online;
> > +
> 
> Hi Tejun,
> 
> What does above mean? One needs to take one lock or both the locks to
> check/modify blkg->online.

Needs both locks to modify, so either lock is enough for checking.

-- 
tejun
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