linux-kernel - Re: INFO: task hung in __get

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Date:   Thu, 16 May 2019 21:50:51 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Jan Kara <jack@...e.cz>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        syzbot <syzbot+10007d66ca02b08f0e60@...kaller.appspotmail.com>,
        dvyukov@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-block@...r.kernel.org
Subject: Re: INFO: task hung in __get_super

On 2019/05/16 21:32, Jan Kara wrote:
> On Thu 16-05-19 21:17:14, Tetsuo Handa wrote:
>> On 2019/05/16 20:48, Jan Kara wrote:
>>> OK, so non-racy fix was a bit more involved and I've ended up just
>>> upgrading the file reference to an exclusive one in loop_set_fd() instead
>>> of trying to hand-craft some locking solution. The result is attached and
>>> it passes blktests.
>>
>> blkdev_get() has corresponding blkdev_put().
>> bdgrab() does not have corresponding bdput() ?
> 
> Yes, and that's hidden inside blkdev_put() (or failing blkdev_get()). Don't
> get me started on calling conventions of these functions... I've wasted half
> an hour trying to figure out where I'm leaking inode references in my patch
> ;).

Ah, found tricky comment. Please apply the patch. Thank you.

/**
 * blkdev_get - open a block device
 * @bdev: block_device to open
 * @mode: FMODE_* mask
 * @holder: exclusive holder identifier
 *
 * Open @bdev with @mode.  If @mode includes %FMODE_EXCL, @bdev is
 * open with exclusive access.  Specifying %FMODE_EXCL with %NULL
 * @holder is invalid.  Exclusive opens may nest for the same @holder.
 *
 * On success, the reference count of @bdev is unchanged.  On failure,
 * @bdev is put.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */