void md_update_sb(struct mddev *mddev, int force_change)
{
	struct md_rdev *rdev;
	int sync_req;
	int nospares = 0;
	int any_badblocks_changed = 0;

	if (mddev->ro) {
		if (force_change)
			set_bit(MD_CHANGE_DEVS, &mddev->flags);
		return;
	}
repeat:
	/* First make sure individual recovery_offsets are correct */
	rdev_for_each(rdev, mddev) {
		if (rdev->raid_disk >= 0 &&
		    mddev->delta_disks >= 0 &&
		    !test_bit(In_sync, &rdev->flags) &&
		    mddev->curr_resync_completed > rdev->recovery_offset)
				rdev->recovery_offset = mddev->curr_resync_completed;

	}
	if (!mddev->persistent) {
		clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
		clear_bit(MD_CHANGE_DEVS, &mddev->flags);
		if (!mddev->external) {
			clear_bit(MD_CHANGE_PENDING, &mddev->flags);
			rdev_for_each(rdev, mddev) {
				if (rdev->badblocks.changed) {
					rdev->badblocks.changed = 0;
					md_ack_all_badblocks(&rdev->badblocks);
					md_error(mddev, rdev);
				}
				clear_bit(Blocked, &rdev->flags);
				clear_bit(BlockedBadBlocks, &rdev->flags);
				wake_up(&rdev->blocked_wait);
			}
		}
		wake_up(&mddev->sb_wait);
		return;
	}

	spin_lock(&mddev->lock);

	mddev->utime = get_seconds();

	if (test_and_clear_bit(MD_CHANGE_DEVS, &mddev->flags))
		force_change = 1;
	if (test_and_clear_bit(MD_CHANGE_CLEAN, &mddev->flags))
		/* just a clean<-> dirty transition, possibly leave spares alone,
		 * though if events isn't the right even/odd, we will have to do
		 * spares after all
		 */
		nospares = 1;
	if (force_change)
		nospares = 0;
	if (mddev->degraded)
		/* If the array is degraded, then skipping spares is both
		 * dangerous and fairly pointless.
		 * Dangerous because a device that was removed from the array
		 * might have a event_count that still looks up-to-date,
		 * so it can be re-added without a resync.
		 * Pointless because if there are any spares to skip,
		 * then a recovery will happen and soon that array won't
		 * be degraded any more and the spare can go back to sleep then.
		 */
		nospares = 0;

	sync_req = mddev->in_sync;

	/* If this is just a dirty<->clean transition, and the array is clean
	 * and 'events' is odd, we can roll back to the previous clean state */
	if (nospares
	    && (mddev->in_sync && mddev->recovery_cp == MaxSector)
	    && mddev->can_decrease_events
	    && mddev->events != 1) {
		mddev->events--;
		mddev->can_decrease_events = 0;
	} else {
		/* otherwise we have to go forward and ... */
		mddev->events ++;
		mddev->can_decrease_events = nospares;
	}

	/*
	 * This 64-bit counter should never wrap.
	 * Either we are in around ~1 trillion A.C., assuming
	 * 1 reboot per second, or we have a bug...
	 */
	WARN_ON(mddev->events == 0);

	rdev_for_each(rdev, mddev) {
		if (rdev->badblocks.changed)
			any_badblocks_changed++;
		if (test_bit(Faulty, &rdev->flags))
			set_bit(FaultRecorded, &rdev->flags);
	}

	sync_sbs(mddev, nospares);
	spin_unlock(&mddev->lock);

	pr_debug("md: updating %s RAID superblock on device (in sync %d)\n",
		 mdname(mddev), mddev->in_sync);

	bitmap_update_sb(mddev->bitmap);
	rdev_for_each(rdev, mddev) {
		char b[BDEVNAME_SIZE];

		if (rdev->sb_loaded != 1)
			continue; /* no noise on spare devices */

		if (!test_bit(Faulty, &rdev->flags)) {
			md_super_write(mddev,rdev,
				       rdev->sb_start, rdev->sb_size,
				       rdev->sb_page);
			pr_debug("md: (write) %s's sb offset: %llu\n",
				 bdevname(rdev->bdev, b),
				 (unsigned long long)rdev->sb_start);
			rdev->sb_events = mddev->events;
			if (rdev->badblocks.size) {
				md_super_write(mddev, rdev,
					       rdev->badblocks.sector,
					       rdev->badblocks.size << 9,
					       rdev->bb_page);
				rdev->badblocks.size = 0;
			}

		} else
			pr_debug("md: %s (skipping faulty)\n",
				 bdevname(rdev->bdev, b));

		if (mddev->level == LEVEL_MULTIPATH)
			/* only need to write one superblock... */
			break;
	}
	md_super_wait(mddev);
	/* if there was a failure, MD_CHANGE_DEVS was set, and we re-write super */

	spin_lock(&mddev->lock);
	if (mddev->in_sync != sync_req ||
	    test_bit(MD_CHANGE_DEVS, &mddev->flags)) {
		/* have to write it out again */
		spin_unlock(&mddev->lock);
		goto repeat;
	}
	clear_bit(MD_CHANGE_PENDING, &mddev->flags);
	spin_unlock(&mddev->lock);
	wake_up(&mddev->sb_wait);
	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
		sysfs_notify(&mddev->kobj, NULL, "sync_completed");

	rdev_for_each(rdev, mddev) {
		if (test_and_clear_bit(FaultRecorded, &rdev->flags))
			clear_bit(Blocked, &rdev->flags);

		if (any_badblocks_changed)
			md_ack_all_badblocks(&rdev->badblocks);
		clear_bit(BlockedBadBlocks, &rdev->flags);
		wake_up(&rdev->blocked_wait);
	}
}