linux-kernel - Re: [PATCH] loop: prevent bdev freeing while device in use

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Message-ID: <20130401162800.GB21522@ZenIV.linux.org.uk>
Date:	Mon, 1 Apr 2013 17:28:00 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Anatol Pomozov <anatol.pomozov@...il.com>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	tytso@....edu, sqazi@...gle.com, yan@...ux.vnet.ibm.com
Subject: Re: [PATCH] loop: prevent bdev freeing while device in use

On Mon, Apr 01, 2013 at 04:58:05AM -0700, Anatol Pomozov wrote:
>  		lo->lo_flags |= LO_FLAGS_PARTSCAN;
>  	if (lo->lo_flags & LO_FLAGS_PARTSCAN)
>  		ioctl_by_bdev(bdev, BLKRRPART, 0);
> +
> +	/* bdev lifecycle is defined by its bd_inode (see
> +	 * struct bdev_inode usage). In case of loop device we need to make
> +	 * sure that bdev deallocation will not happen between loop_set_fd()
> +	 * and loop_clr_fd() invocations. To do this we need to hold
> +	 * bdev inode here and put it later in loop_clr_fd().
> +	 */
> +	ihold(bdev->bd_inode);

That's open-coded bdgrab()

> +	if (bdev) {
> +		BUG_ON(atomic_read(&bdev->bd_inode->i_count) < 2);
> +		iput(bdev->bd_inode);

... and that - bdput() (I'd drop that BUG_ON())
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