The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b879f915bc48a18d4f4462729192435bb0f17052 Mon Sep 17 00:00:00 2001 From: Mike Snitzer snitzer@redhat.com Date: Fri, 28 Jan 2022 10:58:41 -0500 Subject: [PATCH] dm: properly fix redundant bio-based IO accounting

Record the start_time for a bio but defer the starting block core's IO accounting until after IO is submitted using bio_start_io_acct_time().

This approach avoids the need to mess around with any of the individual IO stats in response to a bio_split() that follows bio submission.

Reported-by: Bud Brown bubrown@redhat.com Reviewed-by: Christoph Hellwig hch@lst.de Cc: stable@vger.kernel.org Depends-on: e45c47d1f94e ("block: add bio_start_io_acct_time() to control start_time") Signed-off-by: Mike Snitzer snitzer@redhat.com Link: https://lore.kernel.org/r/20220128155841.39644-4-snitzer@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 9849114b3c08..dcbd6d201619 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -489,7 +489,7 @@ static void start_io_acct(struct dm_io *io) struct mapped_device *md = io->md; struct bio *bio = io->orig_bio;

- io->start_time = bio_start_io_acct(bio); + bio_start_io_acct_time(bio, io->start_time); if (unlikely(dm_stats_used(&md->stats))) dm_stats_account_io(&md->stats, bio_data_dir(bio), bio->bi_iter.bi_sector, bio_sectors(bio), @@ -535,7 +535,7 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio) io->md = md; spin_lock_init(&io->endio_lock);

- start_io_acct(io); + io->start_time = jiffies;

return io; } @@ -1482,6 +1482,7 @@ static void __split_and_process_bio(struct mapped_device *md, submit_bio_noacct(bio); } } + start_io_acct(ci.io);

/* drop the extra reference count */ dm_io_dec_pending(ci.io, errno_to_blk_status(error));