When we add some spares to an array and start recovery, and we have
a bitmap which is stored 'internally' on all devices, we call
bitmap_write_all to make sure the bitmap is correct on the new
device(s).
However that doesn't work as write_sb_page only writes to
'In_sync' devices, and devices undergoing recovery are not
'In_sync' until recovery finishes.
So extend write_sb_page (actually next_active_rdev) to include devices
that are under recovery.
Signed-off-by: NeilBrown <neilb@suse.de>
        list_for_each_continue_rcu(pos, &mddev->disks) {
                rdev = list_entry(pos, mdk_rdev_t, same_set);
                if (rdev->raid_disk >= 0 &&
-                   test_bit(In_sync, &rdev->flags) &&
                    !test_bit(Faulty, &rdev->flags)) {
                        /* this is a usable devices */
                        atomic_inc(&rdev->nr_pending);