linux-kernel - Re: [PATCH UPDATED 11/11] blkcg: unify blkg's for blkcg policies

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Message-ID: <20120203214719.GE14209@google.com>
Date:	Fri, 3 Feb 2012 13:47:19 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH UPDATED 11/11] blkcg: unify blkg's for blkcg policies

On Fri, Feb 03, 2012 at 04:44:35PM -0500, Vivek Goyal wrote:
> Ok, looks like now it is needed because blkcg lock will just gurantee that
> blkg is around but blkg->pd[plid] can disappear if you are not holding
> blkio_list lock (update_root_blkgs).
> 
> I am wondering if we should take blkcg->lock if blkg is on blkcg list and
> is being modified in place. That way, once we are switching elevator,
> we should be able to shoot down the policy data without taking blkio_list
> lock.

I think it gotta become something per-queue, not global, and if we
make it per-queue, it should be able to live inside queue_lock.

Thanks.

-- 
tejun
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