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

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Message-ID: <20120418214255.GA4772@google.com>
Date:	Wed, 18 Apr 2012 14:42:55 -0700
From:	Tejun Heo <tj@...nel.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, 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 Tue, Apr 17, 2012 at 04:04:58PM +0400, James Bottomley wrote:
> > So, the current code is technically correct although subtle like hell.
> > We can RCU defer blk_put_queue() from blk_cleanup_queue() using
> > call_rcu() to make clear that RCU grace period is necessary there.
> > Any better ideas?
> 
> Not really ... except that perhaps we might redo LUN scanning to use
> just a single queue, so repurpose the LUN underneath, but not destroy
> the old queue and setup the new one?  It's a bit counter intuitive, but
> it shouldn't be impossible.

I think we're fine as-is with comment explaining that there can't be
any active dereferencing going on by the time release is reached.

Thanks.

-- 
tejun
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