4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Shaohua Li <s...@fb.com> commit 9c573de3283af007ea11c17bde1e4568d9417328 upstream. blk_queue_split marks bio unmergeable, which makes sense for normal bio. But if dispatching the bio to underlayer disk, the blk_queue_split checks are invalid, hence it's possible the bio becomes mergeable. In the reported bug, this bug causes trim against raid0 performance slash https://bugzilla.kernel.org/show_bug.cgi?id=117051 Reported-and-tested-by: Park Ju Hyung <qkrwngud...@gmail.com> Fixes: 6ac45aeb6bca(block: avoid to merge splitted bio) Cc: Ming Lei <ming....@canonical.com> Cc: Neil Brown <ne...@suse.de> Reviewed-by: Jens Axboe <ax...@fb.com> Signed-off-by: Shaohua Li <s...@fb.com> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- drivers/md/md.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -293,6 +293,8 @@ static blk_qc_t md_make_request(struct r * go away inside make_request */ sectors = bio_sectors(bio); + /* bio could be mergeable after passing to underlayer */ + bio->bi_rw &= ~REQ_NOMERGE; mddev->pers->make_request(mddev, bio); cpu = part_stat_lock();