[PATCH v5 07/29] md: avoid stale clone I/O accounting timestamps

[Yu Kuai <yukuai@kernel.org>]

From: Yu Kuai <yukuai@fygo.io>

md_clone_bio() always allocates the clone from mddev->io_clone_set, even
when queue I/O stats are disabled. In that case it does not call
bio_start_io_acct(), but it also left md_io_clone->start_time untouched.

The clone private data comes from a mempool and can contain data from a
previous user. md_end_clone_io() checks start_time to decide whether it
needs to call bio_end_io_acct(), so a stale non-zero value can make the
completion path end accounting that was never started for this bio.

Set start_time to 0 in the no-stats branch. This keeps the end path tied
to whether bio_start_io_acct() actually ran.

Fixes: c687297b8845 ("md: also clone new io if io accounting is disabled")
Signed-off-by: Yu Kuai <yukuai@fygo.io>
---
 drivers/md/md.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b61040315aef..58fb5453a819 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9448,6 +9448,8 @@ static void md_clone_bio(struct mddev *mddev, struct bio **bio)
 	md_io_clone->mddev = mddev;
 	if (blk_queue_io_stat(bdev->bd_disk->queue))
 		md_io_clone->start_time = bio_start_io_acct(*bio);
+	else
+		md_io_clone->start_time = 0;
 
 	if (bio_data_dir(*bio) == WRITE && md_bitmap_enabled(mddev, false)) {
 		md_io_clone->offset = (*bio)->bi_iter.bi_sector;
-- 
2.51.0