linux-kernel - Re: [PATCH 05/10] block: drop unnecessary blk_get/put_queue() in scsi_cmd_ioctl() and blk_get

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Message-ID: <20111019163528.GC25124@google.com>
Date:	Wed, 19 Oct 2011 09:35:28 -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 05/10] block: drop unnecessary blk_get/put_queue() in
 scsi_cmd_ioctl() and blk_get_tg()

Hey, Vivek.

On Wed, Oct 19, 2011 at 09:52:54AM -0400, Vivek Goyal wrote:
> What makes sure that caller has the reference to the queue upon entry. If
> that's the case, that's good. Just that I had not figured it out so
> resorted to defensive programming as taking extra reference does not harm.

The fact that @q can be dereferenced on entry at all. :)

Taking extra reference doesn't help anything.  If the caller doesn't
have standing reference, it will just change where oops occurs.  W/o
extra ref, it will crash soon after the last reference is put.  W/
extra ref, it will crash after the extra ref is put.  If the caller
doesn't hold a reference, there's nothing the callee can do to fix
that.

Thanks.

-- 
tejun
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