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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: axboe@kernel.dk, pasha.tatashin@soleen.com,
	linux-block@vger.kernel.org,
	Colin Ian King <colin.king@canonical.com>
Subject: Re: [PATCH] block: loop: fix deadlock between open and remove
Date: Mon, 7 Jun 2021 08:11:13 +0800	[thread overview]
Message-ID: <YL1kIY6F7wZ86vU6@T590> (raw)
In-Reply-To: <20210605140950.5800-1-hch@lst.de>

On Sat, Jun 05, 2021 at 05:09:50PM +0300, Christoph Hellwig wrote:
> Commit c76f48eb5c08 ("block: take bd_mutex around delete_partitions in
> del_gendisk") adds disk->part0->bd_mutex in del_gendisk(), this way
> causes the following AB/BA deadlock between removing loop and opening
> loop:
> 
>  1) loop_control_ioctl(LOOP_CTL_REMOVE)
>      -> mutex_lock(&loop_ctl_mutex)
>      -> del_gendisk
>          -> mutex_lock(&disk->part0->bd_mutex)
> 
>  2) blkdev_get_by_dev
>      -> mutex_lock(&disk->part0->bd_mutex)
>      -> lo_open
>          -> mutex_lock(&loop_ctl_mutex)
> 
> Add a new Lo_deleting state to remove the need for clearing
> ->private_data and thus holding loop_ctl_mutex in the ioctl
> LOOP_CTL_REMOVE path.
> 
> Based on an analysis and earlier patch from
> Ming Lei <ming.lei@redhat.com>.
> 
> Reported-by: Colin Ian King <colin.king@canonical.com>
> Fixes: c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk")
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming


  parent reply	other threads:[~2021-06-07  0:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-05 14:09 [PATCH] block: loop: fix deadlock between open and remove Christoph Hellwig
2021-06-05 15:00 ` Colin Ian King
2021-06-07  0:11 ` Ming Lei [this message]
2021-06-11 17:51 ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2021-06-04  0:04 Ming Lei
2021-06-04  6:57 ` Christoph Hellwig
2021-06-04  8:56   ` Ming Lei

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