alinux: blk-mq: fix broken io_ticks & time_in_queue update

fix #25369772

In blk-mq device, we observed a issue that though iops is low, but iostat
shows a very high svctm & util value, which is counter-intuitive.

The root cause is that blk_account_io_start() calls part_round_stats()
before "rq->part = part" statement, so part_round_stats() will count
an inflight request to the whole device, but not for the specific
partition, then it'll update whole device's io_ticks and time_in_queue
with a stale part->stamp.

To fix this issue, if a request's part is NULL, we just don't count
it as an inflight request to the whole device.
Signed-off-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>

block/blk-mq.c

@@ -106,7 +106,7 @@ static void blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx,
 	 */
 	if (rq->part == mi->part)
 		mi->inflight[0]++;
-	if (mi->part->partno)
+	if (rq->part && mi->part->partno)
 		mi->inflight[1]++;
 }