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

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Date:	Mon, 1 Apr 2013 09:49:54 -0700
From:	Anatol Pomozov <anatol.pomozov@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>, sqazi@...gle.com,
	Guo Chao <yan@...ux.vnet.ibm.com>
Subject: Re: [PATCH] loop: prevent bdev freeing while device in use

Hi

On Mon, Apr 1, 2013 at 9:28 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> 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()

Done. It also requires EXPORTING bdgrab.

The test still passes.

>
>> +     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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