BACKPORT: FROMGIT: block: BFQ: Add several invariant checks

If anything goes wrong with the counters that track the number of
requests, I/O locks up. Make such scenarios easier to debug by adding
invariant checks for the request counters. Additionally, check that
BFQ queues are empty before these are freed.

Cc: Jan Kara <jack@suse.cz>
Cc: Yu Kuai <yukuai3@huawei.com>
Change-Id: I566e972e4c9c5c3e8bb256e6be39f5bb6bec7256
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230516223853.1385255-1-bvanassche@acm.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Bug: 275581839
(cherry picked from commit 3e49c1e4 https://git.kernel.dk/cgit/linux/

)
[ bvanassche: backported to kernel v5.15 ]
Signed-off-by: Bart Van Assche <bvanassche@google.com>