linux-kernel - [PATCH 4.2.y-ckt 113/218] md: multipath: don't hardcopy bio in .make

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Message-Id: <1459455431-12687-114-git-send-email-kamal@canonical.com>
Date:	Thu, 31 Mar 2016 13:15:26 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ming Lei <ming.lei@...onical.com>, Shaohua Li <shli@...com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 113/218] md: multipath: don't hardcopy bio in .make_request path

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Ming Lei <ming.lei@...onical.com>

commit fafcde3ac1a418688a734365203a12483b83907a upstream.

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.

Reported-and-tested-by: Andrea Righi <righi.andrea@...il.com>
Signed-off-by: Ming Lei <ming.lei@...onical.com>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 ac3ede2..ac37ef1 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;
-- 
2.7.4