On Sat, 2021-07-17 at 10:07:19 UTC, Desmond Cheong Zhi Xi wrote:
There is a lock hierarchy of major_names_lock --> mtd_table_mutex. One
existing chain is as follows:
1. major_names_lock --> loop_ctl_mutex (when blk_request_module calls
loop_probe)
2. loop_ctl_mutex --> bdev->bd_mutex (when loop_control_ioctl calls
loop_remove, which then calls del_gendisk)
3. bdev->bd_mutex --> mtd_table_mutex (when blkdev_get_by_dev calls
__blkdev_get, which then calls blktrans_open)
Since unregister_blkdev grabs the major_names_lock, we need to call it
outside the critical section for mtd_table_mutex, otherwise we invert
the lock hierarchy.
Reported-by: Hillf Danton <redacted>
Signed-off-by: Desmond Cheong Zhi Xi <redacted>
Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.
Miquel