block/mq-deadline: Add an invariant check

Check a statistics invariant at module unload time. When running
blktests, the invariant is verified every time a request queue is
removed and hence is verified at least once per test.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Niklas Cassel <Niklas.Cassel@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210927220328.1410161-3-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/mq-deadline.c

@@ -270,6 +270,12 @@ deadline_move_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
 	deadline_remove_request(rq->q, per_prio, rq);
 }
 
+/* Number of requests queued for a given priority level. */
+static u32 dd_queued(struct deadline_data *dd, enum dd_prio prio)
+{
+	return dd_sum(dd, inserted, prio) - dd_sum(dd, completed, prio);
+}
+
 /*
  * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
  * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
@@ -539,6 +545,12 @@ static void dd_exit_sched(struct elevator_queue *e)
 
 		WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_READ]));
 		WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_WRITE]));
+		WARN_ONCE(dd_queued(dd, prio) != 0,
+			  "statistics for priority %d: i %u m %u d %u c %u\n",
+			  prio, dd_sum(dd, inserted, prio),
+			  dd_sum(dd, merged, prio),
+			  dd_sum(dd, dispatched, prio),
+			  dd_sum(dd, completed, prio));
 	}
 
 	free_percpu(dd->stats);
@@ -950,12 +962,6 @@ static int dd_async_depth_show(void *data, struct seq_file *m)
 	return 0;
 }
 
-/* Number of requests queued for a given priority level. */
-static u32 dd_queued(struct deadline_data *dd, enum dd_prio prio)
-{
-	return dd_sum(dd, inserted, prio) - dd_sum(dd, completed, prio);
-}
-
 static int dd_queued_show(void *data, struct seq_file *m)
 {
 	struct request_queue *q = data;