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@xxxxxxxxxx>.
>
> Reported-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Fixes: c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk")
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
--
Ming
