md: raid1/raid10: fix problem with merge_bvec_fn

commit aba336bd upstream.

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.
Reported-by: Sebastian Riemer <sebastian.riemer@profitbricks.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/md/raid1.c

@@ -2548,6 +2548,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 	err = -EINVAL;
 	spin_lock_init(&conf->device_lock);
 	rdev_for_each(rdev, mddev) {
+		struct request_queue *q;
 		int disk_idx = rdev->raid_disk;
 		if (disk_idx >= mddev->raid_disks
 		    || disk_idx < 0)
@@ -2560,6 +2561,9 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 		if (disk->rdev)
 			goto abort;
 		disk->rdev = rdev;
+		q = bdev_get_queue(rdev->bdev);
+		if (q->merge_bvec_fn)
+			mddev->merge_check_needed = 1;
 
 		disk->head_position = 0;
 	}

drivers/md/raid10.c

@@ -3311,7 +3311,7 @@ static int run(struct mddev *mddev)
 				 (conf->raid_disks / conf->near_copies));
 
 	rdev_for_each(rdev, mddev) {
-
+		struct request_queue *q;
 		disk_idx = rdev->raid_disk;
 		if (disk_idx >= conf->raid_disks
 		    || disk_idx < 0)
@@ -3327,6 +3327,9 @@ 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;
 
 		disk_stack_limits(mddev->gendisk, rdev->bdev,
 				  rdev->data_offset << 9);