Found when trying to reassemble an active externally managed array.  Without
this check we hit the more noisy "sysfs duplicate" warning in the later call
to kobject_add.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
                MD_BUG();
                return -EINVAL;
        }
+
+       /* prevent duplicates */
+       if (find_rdev(mddev, rdev->bdev->bd_dev))
+               return -EEXIST;
+
        /* make sure rdev->size exceeds mddev->size */
        if (rdev->size && (mddev->size == 0 || rdev->size < mddev->size)) {
                if (mddev->pers) {