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

From: Tejun Heo
Date: Fri Feb 03 2012 - 16:47:22 EST

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.


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