md: return -ENODEV if rdev has no mddev assigned

Mdadm expects that setting drive as faulty will fail with -EBUSY only if
this operation will cause RAID to be failed. If this happens, it will
try to stop the array. Currently -EBUSY might also be returned if rdev
is in the middle of the removal process - for example there is a race
with mdmon that already requested the drive to be failed/removed.

If rdev does not contain mddev, return -ENODEV instead, so the caller
can distinguish between those two cases and behave accordingly.
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Pawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/md.c

@@ -3380,10 +3380,10 @@ rdev_attr_store(struct kobject *kobj, struct attribute *attr,
 		return -EIO;
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
-	rv = mddev ? mddev_lock(mddev): -EBUSY;
+	rv = mddev ? mddev_lock(mddev) : -ENODEV;
 	if (!rv) {
 		if (rdev->mddev == NULL)
-			rv = -EBUSY;
+			rv = -ENODEV;
 		else
 			rv = entry->store(rdev, page, length);
 		mddev_unlock(mddev);