[PATCH 3/3] blkcg: account cgroup v1 I/O before checking throttle activation

[Zhe Liu]

Commit a3166c51702b ("blk-throttle: delay initialization until
configuration") made throttle policy activation conditional on
configuring a limit. However, blk_should_throtl() returns before
updating the v1 counters when the policy is inactive. A cgroup v1
workload that only monitors I/O therefore gets no accounting until a
limit is configured on the device.

Now that the counters belong to the blkg, move their updates out of
blk_should_throtl() and account immediately before blk_throtl_bio() in
both submit_bio_noacct() and bio_submit_split_bioset(). This records I/O
even when the throttle policy has never been activated.

Keep BIO_CGROUP_ACCT byte deduplication and count each split-remainder
submission as an I/O. Throttle worker dispatch continues to use the
nocheck submission path, avoiding a second accounting update. The
inline hierarchy check skips v1 accounting on cgroup v2.

Fixes: a3166c51702b ("blk-throttle: delay initialization until configuration")
Signed-off-by: Zhe Liu <liuzhe1@xxxxxxxxxx>
---
 block/blk-core.c     | 1 +
 block/blk-merge.c    | 9 ++++++---
 block/blk-throttle.h | 1 -
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 8836c7028568..013d806efb43 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -924,6 +924,7 @@ void submit_bio_noacct(struct bio *bio)
 		goto not_supported;
 	}
 
+	blkcg_account_v1_bio(bio);
 	if (blk_throtl_bio(bio))
 		return;
 	submit_bio_noacct_nocheck(bio, false);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 501ddc01c449..8bc996002646 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -131,10 +131,13 @@ struct bio *bio_submit_split_bioset(struct bio *bio, unsigned int split_sectors,
 	trace_block_split(split, bio->bi_iter.bi_sector);
 	WARN_ON_ONCE(bio_zone_write_plugging(bio));
 
-	if (should_fail_bio(bio))
+	if (should_fail_bio(bio)) {
 		bio_io_error(bio);
-	else if (!blk_throtl_bio(bio))
-		submit_bio_noacct_nocheck(bio, true);
+	} else {
+		blkcg_account_v1_bio(bio);
+		if (!blk_throtl_bio(bio))
+			submit_bio_noacct_nocheck(bio, true);
+	}
 
 	return split;
 }
diff --git a/block/blk-throttle.h b/block/blk-throttle.h
index 02c08daf3dc3..73f0d4bbdc71 100644
--- a/block/blk-throttle.h
+++ b/block/blk-throttle.h
@@ -170,7 +170,6 @@ static inline bool blk_should_throtl(struct bio *bio)
 		return false;
 
 	tg = blkg_to_tg(bio->bi_blkg);
-	blkcg_account_v1_bio(bio);
 
 	/* iops limit is always counted */
 	if (tg->has_rules_iops[rw])
-- 
2.25.1