block: fix inaccurate io_ticks

hulk inclusion
category: bugfix
bugzilla: 31388
CVE: NA
---------------------------

After introducing commit 5b18b5a73760 ("block: delete part_round_stats
and switch to less precise counting"), '%util' accounted by iostat
will be over reality data. In fact, the device is quite idle, but
iostat may show '%util' as a big number (e.g. 50%). It can produce by fio:

fio --name=1 --direct=1 --bs=4k --rw=read --filename=/dev/sda \
                   --thinktime=4ms --runtime=180

We fix this by reserving part_round_stats() in io start path.

fixes: 5b18b5a73760 ("block: delete part_round_stats and switch to less precise counting")
Signed-off-by: NYufen Yu <yuyufen@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

block/bio.c

@@ -1675,7 +1675,7 @@ void update_io_ticks(int cpu, struct hd_struct *part, unsigned long now)
 	stamp = READ_ONCE(part->stamp);
 	if (unlikely(stamp != now)) {
 		if (likely(cmpxchg(&part->stamp, stamp, now) == stamp))
-			__part_stat_add(cpu, part, io_ticks, 1);
+			__part_stat_add(cpu, part, io_ticks, now - stamp);
 	}
 	if (part->partno) {
 		part = &part_to_disk(part)->part0;
@@ -1689,7 +1689,7 @@ void generic_start_io_acct(struct request_queue *q, int op,
 	const int sgrp = op_stat_group(op);
 	int cpu = part_stat_lock();
 
-	update_io_ticks(cpu, part, jiffies);
+	part_round_stats(q, cpu, part);
 	part_stat_inc(cpu, part, ios[sgrp]);
 	part_stat_add(cpu, part, sectors[sgrp], sectors);
 	part_inc_in_flight(q, part, op_is_write(op));

block/blk-core.c

@@ -1674,11 +1674,8 @@ static void part_round_stats_single(struct request_queue *q, int cpu,
 				    struct hd_struct *part, unsigned long now,
 				    unsigned int inflight)
 {
-	if (inflight) {
-		__part_stat_add(cpu, part, time_in_queue,
-				inflight * (now - part->stamp));
+	if (inflight)
 		__part_stat_add(cpu, part, io_ticks, (now - part->stamp));
-	}
 	part->stamp = now;
 }
 
@@ -2791,12 +2788,11 @@ void blk_account_io_start(struct request *rq, bool new_io)
 		part_stat_inc(cpu, part, merges[rw]);
 	} else {
 		part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
+		part_round_stats(rq->q, cpu, part);
 		part_inc_in_flight(rq->q, part, rw);
 		rq->part = part;
 	}
 
-	update_io_ticks(cpu, part, jiffies);
-
 	part_stat_unlock();
 }