[PATCH 4.17 210/220] dm: use bio_split() when splitting out the already processed bio

From: Greg Kroah-Hartman
Date: Sun Jul 01 2018 - 12:46:28 EST

4.17-stable review patch. If anyone has any objections, please let me know.


From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit f21c601a2bb319ec19eb4562eadc7797d90fd90e upstream.

Use of bio_clone_bioset() is inefficient if there is no need to clone
the original bio's bio_vec array. Best to use the bio_clone_fast()
variant. Also, just using bio_advance() is only part of what is needed
to properly setup the clone -- it doesn't account for the various
bio_integrity() related work that also needs to be performed (see

Address both of these issues by switching from bio_clone_bioset() to

Fixes: 18a25da8 ("dm: ensure bio submission follows a depth-first tree walk")
Cc: stable@xxxxxxxxxxxxxxx # 4.15+, requires removal of '&' before md->queue->bio_split
Reported-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/md/dm.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1582,10 +1582,9 @@ static blk_qc_t __split_and_process_bio(
* the usage of io->orig_bio in dm_remap_zone_report()
* won't be affected by this reassignment.
- struct bio *b = bio_clone_bioset(bio, GFP_NOIO,
- md->queue->bio_split);
+ struct bio *b = bio_split(bio, bio_sectors(bio) - ci.sector_count,
+ GFP_NOIO, md->queue->bio_split);
ci.io->orig_bio = b;
- bio_advance(bio, (bio_sectors(bio) - ci.sector_count) << 9);
bio_chain(b, bio);
ret = generic_make_request(bio);