On Sun, Aug 15, 2021 at 07:27:37AM -0700, Guenter Roeck wrote:

[   14.467748][    T1]  Possible unsafe locking scenario:
[   14.467748][    T1]
[   14.467928][    T1]        CPU0                    CPU1
[   14.468058][    T1]        ----                    ----
[   14.468187][    T1]   lock(&disk->open_mutex);
[   14.468317][    T1]                                lock(mtd_table_mutex);
[   14.468493][    T1]                                lock(&disk->open_mutex);
[   14.468671][    T1]   lock(mtd_table_mutex);

Oh, that ooks like a really old one, fixed by
b7abb0516822 ("mtd: fix lock hierarchy in deregister_mtd_blktrans")
in linux-next.