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>
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>

block/bfq-iosched.c

@@ -5403,6 +5403,9 @@ void bfq_put_queue(struct bfq_queue *bfqq)
 	if (bfqq->bfqd->last_completed_rq_bfqq == bfqq)
 		bfqq->bfqd->last_completed_rq_bfqq = NULL;
 
+	WARN_ON_ONCE(!list_empty(&bfqq->fifo));
+	WARN_ON_ONCE(!RB_EMPTY_ROOT(&bfqq->sort_list));
+
 	kmem_cache_free(bfq_pool, bfqq);
 	bfqg_and_blkg_put(bfqg);
 }
@@ -7135,6 +7138,7 @@ static void bfq_exit_queue(struct elevator_queue *e)
 {
 	struct bfq_data *bfqd = e->elevator_data;
 	struct bfq_queue *bfqq, *n;
+	unsigned int actuator;
 
 	hrtimer_cancel(&bfqd->idle_slice_timer);
 
@@ -7143,6 +7147,11 @@ static void bfq_exit_queue(struct elevator_queue *e)
 		bfq_deactivate_bfqq(bfqd, bfqq, false, false);
 	spin_unlock_irq(&bfqd->lock);
 
+	for (actuator = 0; actuator < bfqd->num_actuators; actuator++)
+		WARN_ON_ONCE(bfqd->rq_in_driver[actuator]);
+	WARN_ON_ONCE(bfqd->tot_rq_in_driver);
+	WARN_ON_ONCE(bfqq->dispatched);
+
 	hrtimer_cancel(&bfqd->idle_slice_timer);
 
 	/* release oom-queue reference to root group */