linux-kernel - Re: [PATCH] blkio: Release blkg infrastructure only after last policy is deactivated.

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Message-ID: <20140624210930.GD14909@htj.dyndns.org>
Date:	Tue, 24 Jun 2014 17:09:30 -0400
From:	Tejun Heo <tj@...nel.org>
To:	shirishpargaonkar@...il.com
Cc:	linux-kernel@...r.kernel.org, vgoyal@...hat.com,
	Shirish Pargaonkar <spargaonkar@...e.com>
Subject: Re: [PATCH] blkio: Release blkg infrastructure only after last
 policy is deactivated.

Hello,

On Mon, Jun 23, 2014 at 01:52:25PM -0500, shirishpargaonkar@...il.com wrote:
> From: Shirish Pargaonkar <spargaonkar@...e.com>
> 
> Release blkg infrastructure only after last policy is deactivated
> (i.e. let blkg_destroy_all() be called only from blkcg_deactivate_policy())
> 
> Otherwise, module can oops because root_blkg gets assigned NULL during
> cleanup and we attempt draining the service queues via root_blkg afterwords.

I'm not sure this fix makes sense.  Cleanup path oopses on an already
freed resource.  How can the solution be not freeing?  Why not simply
make blkcg_drain_queue() bail if the blkgs are all destroyed?  The
whole thing is fully synchronized with the queuelock, right?

Can you please also cc Jens when you post the next iteration?

Thanks.

-- 
tejun
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