[BUG] kernel BUG at mm/slub.c - possible BFQ issue?

Hello,

I encounter a hard freeze on both 5.14 and 5.15 when using BFQ.
Unfortunately, I do not have a full error log, because the computer
totally freezes and slightly corrupts the display, so it's
impossible to read the entire message.

However, what I could get is the following:

  kernel BUG at mm/slub.c:379
  invalid opcode: 0000 [#1]
  RIP: 0010:__slab_free
  [...]
  Call Trace:
  bfq_set_next_ioprio_data
  [...]
  bfq_put_queue
  bfq_insert_requests
  [...]

This issue appears more or less randomly and it sometimes takes a
little while to reproduce it (running fio helps).
The call trace always contains references to BFQ, but they are not
always the exact same. Once, I could see on the corrupted display
the message "general protection fault".
I could reproduce this issue on two computers.

Not quite sure but I *think* the issue first appeared somewhere around
5.14.5 or 5.14.6, during which time BFQ only got the following commit:

  (88013a0c5d99) block, bfq: honor already-setup queue merges

5.13 doesn't seem to be affected AFAICS.

Does anyone have an idea what is going on?
I will now revert the above commit and see if that helps...

Thanks,
Tor