drbd: merge_bvec_fn: properly remap bvm->bi_bdev

This was not noticed for many years. Affects operation if
md raid is used a backing device for DRBD.

CC: stable@kernel.org # v3.2+
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 5a01c53dddeb873b5fdba6d4d06e3c9f18476a41..90319b14d5ee1032d53aec65acf3edf8469b9c75 100644 (file)
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1545,6 +1545,7 @@ int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct
                struct request_queue * const b =
                        device->ldev->backing_bdev->bd_disk->queue;
                if (b->merge_bvec_fn) {
+                       bvm->bi_bdev = device->ldev->backing_bdev;
                        backing_limit = b->merge_bvec_fn(b, bvm, bvec);
                        limit = min(limit, backing_limit);
                }