block: loop: fix deadlock between open and remove

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 <[email protected]>.

Reported-by: Colin Ian King <[email protected]>
Fixes: c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk")
Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Colin Ian King <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions