[dm-devel] [PATCH] dm: fix bio length of empty flush

[Shin'ichiro Kawasaki]

The commit 92986f6b4c8a ("dm: use bio_clone_fast in alloc_io/alloc_tio")
removed bio_clone_fast() call from alloc_tio() when ci->io->tio is
available. In this case, ci->bio is not copied to ci->io->tio.clone.
This is fine since init_clone_info() sets same values to ci->bio and
ci->io->tio.clone.

However, when incoming bios have REQ_PREFLUSH flag, __send_empty_flush()
prepares a zero length bio on stack and set it to ci->bio. At this time,
ci->io->tio.clone still keeps non-zero length. When alloc_tio() chooses
this ci->io->tio.clone as the bio to map, it is passed to targets as
non-empty flush bio. It causes bio length check failure in dm-zoned and
unexpected operation such as dm_accept_partial_bio() call.

To avoid the non-empty flush bio, set zero length to ci->io->tio.clone
in __send_empty_flush().

Fixes: 92986f6b4c8a ("dm: use bio_clone_fast in alloc_io/alloc_tio")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki at wdc.com>
---
 drivers/md/dm.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3c5fad7c4ee6..f2397546b93f 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1392,6 +1392,7 @@ static void __send_empty_flush(struct clone_info *ci)
 
 	ci->bio = &flush_bio;
 	ci->sector_count = 0;
+	ci->io->tio.clone.bi_iter.bi_size = 0;
 
 	while ((ti = dm_table_get_target(ci->map, target_nr++)))
 		__send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL);
-- 
2.35.1