linux-kernel - Re: [PATCH 07/11] blkcg: make request

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Message-ID: <20120413210548.GG12233@google.com>
Date:	Fri, 13 Apr 2012 14:05:48 -0700
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, cgroups@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH 07/11] blkcg: make request_queue bypassing on allocation

On Fri, Apr 13, 2012 at 04:55:01PM -0400, Vivek Goyal wrote:
> But neither seems to be the case here. So to make sure that blkg_lookup()
> under rcu will see the updated value of queue flag (bypass), are we
> relying on the fact that caller should see the DEAD flag and not go
> ahead with blkg_lookup()?  If yes, atleast it is not obivious.

We're relying on the fact that it doesn't matter anymore because all
blkgs will be shoot down in queue cleanup path which goes through rcu
free, which is different from deactivating individual policies.  It
indeed is subtle.  Umm... this is starting to get ridiculous.  Why the
hell was megaraid messing with so many queues anyways?

Thanks.

-- 
tejun
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