Commit ae7eb31e authored by Yu Kuai's avatar Yu Kuai Committed by Zheng Zengkai
Browse files

block: fix that iostat can show huge wait time 

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I57S8D


CVE: NA

--------------------------------

There might be a problem that iostat can read less 'nsecs' than the
last time.

1) io is started after 'hd->stat_time' is set.

2) following concurrent scenario:

t1                              t2
                                blk_mq_end_request
				 time1 -> before hd->stat_time

				 blk_account_io_done
part_get_stat_info
 part_set_stat_time
  hd->stat_time = time2
  -> time1 < time2
 blk_mq_in_flight_with_stat
  blk_mq_check_inflight_with_stat
   cmpxchg64()
   -> set stat_time_ns to time2
				  cmpxchg64()
				  -> set stat_time to time1
				  duation = time1 - time2;
				  -> time1 < time2
				  part_stat_add(xx, nsecs, duation)
				  -> problematic

3) Similar concurrent scenario the other way around.

Fix the problem by don't add 'duation' if the calculation might underflow.

Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Reviewed-by: default avatarJason Yan <yanaijie@huawei.com>
Signed-off-by: default avatarZheng Zengkai <zhengzengkai@huawei.com>
parent 8d1b294d

block/blk-core.c

+2 −1
Original line number Diff line number Diff line
@@ -1304,7 +1304,8 @@ void blk_account_io_done(struct request *req, u64 now) 
		 * This might fail if 'stat_time_ns' is updated

		 * in blk_mq_check_inflight_with_stat().

		 */

		if (likely(cmpxchg64(&rq_wrapper->stat_time_ns, stat_time, now)

		if (likely(now > stat_time &&

			   cmpxchg64(&rq_wrapper->stat_time_ns, stat_time, now)

			   == stat_time)) {

			u64 duation = stat_time ? now - stat_time :

				now - req->start_time_ns;

block/blk-mq.c

+10 −2
Original line number Diff line number Diff line
@@ -117,13 +117,21 @@ static bool blk_mq_check_inflight_with_stat(struct blk_mq_hw_ctx *hctx, 
		if (!rq->part)

			return true;



		/*

		 * If the request is started after 'part->stat_time' is set,

		 * don't update 'nsces' here.

		 */

		if (rq->part->stat_time <= rq->start_time_ns)

			return true;



		rq_wrapper = request_to_wrapper(rq);

		stat_time = READ_ONCE(rq_wrapper->stat_time_ns);

		/*

		 * This might fail if 'stat_time_ns' is updated in

		 * blk_account_io_done().

		 */

		if (likely(cmpxchg64(&rq_wrapper->stat_time_ns, stat_time,

		if (likely(rq->part->stat_time > stat_time &&

			   cmpxchg64(&rq_wrapper->stat_time_ns, stat_time,

				     rq->part->stat_time) == stat_time)) {

			int sgrp = op_stat_group(req_op(rq));

			u64 duation = stat_time ?