md: raid1/raid10: fix problem with merge_bvec_fn

The new merge_bvec_fn which calls the corresponding function
in subsidiary devices requires that mddev->merge_check_needed
be set if any child has a merge_bvec_fn.

However were were only setting that when a device was hot-added,
not when a device was present from the start.

This bug was introduced in 3.4 so patch is suitable for 3.4.y
kernels.  However that are conflicts in raid10.c so a separate
patch will be needed for 3.4.y.

Cc: stable@vger.kernel.org
Reported-by: Sebastian Riemer <sebastian.riemer@profitbricks.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 987db37cb875..99ae6068e456 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3475,6 +3475,7 @@ static int run(struct mddev *mddev)
 
         rdev_for_each(rdev, mddev) {
                 long long diff;
+                struct request_queue *q;
 
                 disk_idx = rdev->raid_disk;
                 if (disk_idx < 0)
@@ -3493,6 +3494,9 @@ static int run(struct mddev *mddev)
                                 goto out_free_conf;
                         disk->rdev = rdev;
                 }
+                q = bdev_get_queue(rdev->bdev);
+                if (q->merge_bvec_fn)
+                        mddev->merge_check_needed = 1;
                 diff = (rdev->new_data_offset - rdev->data_offset);
                 if (!mddev->reshape_backwards)
                         diff = -diff;