Re: [PATCH 1/6] block: export blkdev_reread_part()

From: Ming Lei <ming.lei@canonical.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Tejun Heo <tj@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jarod Wilson <jarod@redhat.com>,
	David Herrmann <dh.herrmann@gmail.com>,
	Markus Pargmann <mpa@pengutronix.de>,
	"nbd-general@lists.sourceforge.net" 
	<nbd-general@lists.sourceforge.net>,
	Stefan Haberland <stefan.haberland@de.ibm.com>,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	Fabian Frederick <fabf@skynet.be>,
	linux-s390@vger.kernel.org
Subject: Re: [PATCH 1/6] block: export blkdev_reread_part()
Date: Tue, 7 Apr 2015 10:11:53 +0800	[thread overview]
Message-ID: <CACVXFVNHpUyM3QYUKCxvhx9N2ec0=pcLY2snCt-BOX_dqZtTHw@mail.gmail.com> (raw)
In-Reply-To: <20150406145048.GC2703@infradead.org>

On Mon, Apr 6, 2015 at 10:50 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, Apr 06, 2015 at 12:40:12AM +0800, Ming Lei wrote:
>> > int blkdev_reread_part(struct block_device *bdev)
>> > {
>> >         if (!mutex_trylock(&bdev->bd_mutex))
>> >                 return -EBUSY;
>> >         blkdev_reread_part_nolock(bdev);
>> >         mutex_unlock(&bdev->bd_mutex);
>> > }
>>
>> Yes, it is more clean, but with extra acquiring lock cost for the
>> failure cases, especially when we replace trylock with mutex_lock().
>
> It's just a few fairly trivial checks, so 'm not really worried about
> it, especially given that blkdev_reread_part isn't called from a fast
> path.

OK, considered that common users don't have any privilege
on block devices at default in most distributions, so they can't
do DoS by running ioctl(RRPART) with this change.

I will change to this style in v1.

Thanks,
Ming Lei