[added to the 3.18 stable tree] md: multipath: don't hardcopy bio in .make_request path

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From: Ming Lei <ming.lei@xxxxxxxxxxxxx>

This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit fafcde3ac1a418688a734365203a12483b83907a ]

Inside multipath_make_request(), multipath maps the incoming
bio into low level device's bio, but it is totally wrong to
copy the bio into mapped bio via '*mapped_bio = *bio'. For
example, .__bi_remaining is kept in the copy, especially if
the incoming bio is chained to via bio splitting, so .bi_end_io
can't be called for the mapped bio at all in the completing path
in this kind of situation.

This patch fixes the issue by using clone style.

Cc: stable@xxxxxxxxxxxxxxx (v3.14+)
Reported-and-tested-by: Andrea Righi <righi.andrea@xxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 drivers/md/multipath.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/multipath.c b/drivers/md/multipath.c
index 399272f..2df218d 100644
--- a/drivers/md/multipath.c
+++ b/drivers/md/multipath.c
@@ -129,7 +129,9 @@ static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 	}
 	multipath = conf->multipaths + mp_bh->path;
 
-	mp_bh->bio = *bio;
+	bio_init(&mp_bh->bio);
+	__bio_clone_fast(&mp_bh->bio, bio);
+
 	mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;
 	mp_bh->bio.bi_bdev = multipath->rdev->bdev;
 	mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
-- 
2.5.0

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