linux-kernel - Re: [PATCH 1/6] block: export blkdev_reread

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Date:	Sun, 5 Apr 2015 09:12:41 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jarod Wilson <jarod@...hat.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Markus Pargmann <mpa@...gutronix.de>,
	nbd-general@...ts.sourceforge.net,
	Stefan Haberland <stefan.haberland@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Fabian Frederick <fabf@...net.be>, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/6] block: export blkdev_reread_part()

> +/*
> + * This is exported as API for block driver, can be called
> + * with requiring bd_mutex or not.
> + */
> +int __blkdev_reread_part(struct block_device *bdev, bool lock)
>  {
>  	struct gendisk *disk = bdev->bd_disk;
>  	int res;
> @@ -159,12 +163,14 @@ static int blkdev_reread_part(struct block_device *bdev)
>  		return -EINVAL;
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EACCES;
> -	if (!mutex_trylock(&bdev->bd_mutex))
> +	if (lock && !mutex_trylock(&bdev->bd_mutex))
>  		return -EBUSY;

Please don't add funtions that do conditional locking, instead move
all the code into blkdev_reread_part_nolock, and then wrap it:

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);
}

Please also add a lockdep_assert_held to blkdev_reread_part_nolock to
ensure callers actually do hold the lock.
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