linux-kernel - Re: [PATCH 02/10] block: fix genhd refcounting in blkio_policy_parse_and

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Date:	Wed, 19 Oct 2011 09:29:02 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, ctalbott@...gle.com,
	rni@...gle.com
Subject: Re: [PATCH 02/10] block: fix genhd refcounting in
 blkio_policy_parse_and_set()

Hello,

On Wed, Oct 19, 2011 at 09:26:57AM -0400, Vivek Goyal wrote:
> What's the advantage of collapsing blkio_check_dev_num(). Why not put the
> reference to gendisk in this function before returning either success or
> failure.

Heh, at first, I just thought there would be something which depends
on disk still being around in the code path as unsynchronized one time
check upfront doesn't really guarantee anything; then, I realized
there was nothing, but I still left it like that because I personally
think blkio_check_dev_num() w/o surrounding exclusion is a bad
interface.  It's at best opportunistic and likely to mislead people
into believing that there's some magical implied synchronization.

Also, I'm planning on cleaning up synchronization around iocg and for
it to work properly, it'll be necessary to do proper ref counting and
removal on release anyway.

Thanks.

-- 
tejun
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