int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
			     u64 group_start, struct extent_map *em)
{
	struct btrfs_fs_info *fs_info = trans->fs_info;
	struct btrfs_path *path;
	struct btrfs_block_group *block_group;
	struct btrfs_free_cluster *cluster;
	struct inode *inode;
	struct kobject *kobj = NULL;
	int ret;
	int index;
	int factor;
	struct btrfs_caching_control *caching_ctl = NULL;
	bool remove_em;
	bool remove_rsv = false;

	block_group = btrfs_lookup_block_group(fs_info, group_start);
	BUG_ON(!block_group);
	BUG_ON(!block_group->ro);

	trace_btrfs_remove_block_group(block_group);
	/*
	 * Free the reserved super bytes from this block group before
	 * remove it.
	 */
	btrfs_free_excluded_extents(block_group);
	btrfs_free_ref_tree_range(fs_info, block_group->start,
				  block_group->length);

	index = btrfs_bg_flags_to_raid_index(block_group->flags);
	factor = btrfs_bg_type_to_factor(block_group->flags);

	/* make sure this block group isn't part of an allocation cluster */
	cluster = &fs_info->data_alloc_cluster;
	spin_lock(&cluster->refill_lock);
	btrfs_return_cluster_to_free_space(block_group, cluster);
	spin_unlock(&cluster->refill_lock);

	/*
	 * make sure this block group isn't part of a metadata
	 * allocation cluster
	 */
	cluster = &fs_info->meta_alloc_cluster;
	spin_lock(&cluster->refill_lock);
	btrfs_return_cluster_to_free_space(block_group, cluster);
	spin_unlock(&cluster->refill_lock);

	btrfs_clear_treelog_bg(block_group);

	path = btrfs_alloc_path();
	if (!path) {
		ret = -ENOMEM;
		goto out;
	}

	/*
	 * get the inode first so any iput calls done for the io_list
	 * aren't the final iput (no unlinks allowed now)
	 */
	inode = lookup_free_space_inode(block_group, path);

	mutex_lock(&trans->transaction->cache_write_mutex);
	/*
	 * Make sure our free space cache IO is done before removing the
	 * free space inode
	 */
	spin_lock(&trans->transaction->dirty_bgs_lock);
	if (!list_empty(&block_group->io_list)) {
		list_del_init(&block_group->io_list);

		WARN_ON(!IS_ERR(inode) && inode != block_group->io_ctl.inode);

		spin_unlock(&trans->transaction->dirty_bgs_lock);
		btrfs_wait_cache_io(trans, block_group, path);
		btrfs_put_block_group(block_group);
		spin_lock(&trans->transaction->dirty_bgs_lock);
	}

	if (!list_empty(&block_group->dirty_list)) {
		list_del_init(&block_group->dirty_list);
		remove_rsv = true;
		btrfs_put_block_group(block_group);
	}
	spin_unlock(&trans->transaction->dirty_bgs_lock);
	mutex_unlock(&trans->transaction->cache_write_mutex);

	ret = btrfs_remove_free_space_inode(trans, inode, block_group);
	if (ret)
		goto out;

	spin_lock(&fs_info->block_group_cache_lock);
	rb_erase(&block_group->cache_node,
		 &fs_info->block_group_cache_tree);
	RB_CLEAR_NODE(&block_group->cache_node);

	/* Once for the block groups rbtree */
	btrfs_put_block_group(block_group);

	if (fs_info->first_logical_byte == block_group->start)
		fs_info->first_logical_byte = (u64)-1;
	spin_unlock(&fs_info->block_group_cache_lock);

	down_write(&block_group->space_info->groups_sem);
	/*
	 * we must use list_del_init so people can check to see if they
	 * are still on the list after taking the semaphore
	 */
	list_del_init(&block_group->list);
	if (list_empty(&block_group->space_info->block_groups[index])) {
		kobj = block_group->space_info->block_group_kobjs[index];
		block_group->space_info->block_group_kobjs[index] = NULL;
		clear_avail_alloc_bits(fs_info, block_group->flags);
	}
	up_write(&block_group->space_info->groups_sem);
	clear_incompat_bg_bits(fs_info, block_group->flags);
	if (kobj) {
		kobject_del(kobj);
		kobject_put(kobj);
	}

	if (block_group->has_caching_ctl)
		caching_ctl = btrfs_get_caching_control(block_group);
	if (block_group->cached == BTRFS_CACHE_STARTED)
		btrfs_wait_block_group_cache_done(block_group);
	if (block_group->has_caching_ctl) {
		spin_lock(&fs_info->block_group_cache_lock);
		if (!caching_ctl) {
			struct btrfs_caching_control *ctl;

			list_for_each_entry(ctl,
				    &fs_info->caching_block_groups, list)
				if (ctl->block_group == block_group) {
					caching_ctl = ctl;
					refcount_inc(&caching_ctl->count);
					break;
				}
		}
		if (caching_ctl)
			list_del_init(&caching_ctl->list);
		spin_unlock(&fs_info->block_group_cache_lock);
		if (caching_ctl) {
			/* Once for the caching bgs list and once for us. */
			btrfs_put_caching_control(caching_ctl);
			btrfs_put_caching_control(caching_ctl);
		}
	}

	spin_lock(&trans->transaction->dirty_bgs_lock);
	WARN_ON(!list_empty(&block_group->dirty_list));
	WARN_ON(!list_empty(&block_group->io_list));
	spin_unlock(&trans->transaction->dirty_bgs_lock);

	btrfs_remove_free_space_cache(block_group);

	spin_lock(&block_group->space_info->lock);
	list_del_init(&block_group->ro_list);

	if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
		WARN_ON(block_group->space_info->total_bytes
			< block_group->length);
		WARN_ON(block_group->space_info->bytes_readonly
			< block_group->length - block_group->zone_unusable);
		WARN_ON(block_group->space_info->bytes_zone_unusable
			< block_group->zone_unusable);
		WARN_ON(block_group->space_info->disk_total
			< block_group->length * factor);
	}
	block_group->space_info->total_bytes -= block_group->length;
	block_group->space_info->bytes_readonly -=
		(block_group->length - block_group->zone_unusable);
	block_group->space_info->bytes_zone_unusable -=
		block_group->zone_unusable;
	block_group->space_info->disk_total -= block_group->length * factor;

	spin_unlock(&block_group->space_info->lock);

	/*
	 * Remove the free space for the block group from the free space tree
	 * and the block group's item from the extent tree before marking the
	 * block group as removed. This is to prevent races with tasks that
	 * freeze and unfreeze a block group, this task and another task
	 * allocating a new block group - the unfreeze task ends up removing
	 * the block group's extent map before the task calling this function
	 * deletes the block group item from the extent tree, allowing for
	 * another task to attempt to create another block group with the same
	 * item key (and failing with -EEXIST and a transaction abort).
	 */
	ret = remove_block_group_free_space(trans, block_group);
	if (ret)
		goto out;

	ret = remove_block_group_item(trans, path, block_group);
	if (ret < 0)
		goto out;

	spin_lock(&block_group->lock);
	block_group->removed = 1;
	/*
	 * At this point trimming or scrub can't start on this block group,
	 * because we removed the block group from the rbtree
	 * fs_info->block_group_cache_tree so no one can't find it anymore and
	 * even if someone already got this block group before we removed it
	 * from the rbtree, they have already incremented block_group->frozen -
	 * if they didn't, for the trimming case they won't find any free space
	 * entries because we already removed them all when we called
	 * btrfs_remove_free_space_cache().
	 *
	 * And we must not remove the extent map from the fs_info->mapping_tree
	 * to prevent the same logical address range and physical device space
	 * ranges from being reused for a new block group. This is needed to
	 * avoid races with trimming and scrub.
	 *
	 * An fs trim operation (btrfs_trim_fs() / btrfs_ioctl_fitrim()) is
	 * completely transactionless, so while it is trimming a range the
	 * currently running transaction might finish and a new one start,
	 * allowing for new block groups to be created that can reuse the same
	 * physical device locations unless we take this special care.
	 *
	 * There may also be an implicit trim operation if the file system
	 * is mounted with -odiscard. The same protections must remain
	 * in place until the extents have been discarded completely when
	 * the transaction commit has completed.
	 */
	remove_em = (atomic_read(&block_group->frozen) == 0);
	spin_unlock(&block_group->lock);

	if (remove_em) {
		struct extent_map_tree *em_tree;

		em_tree = &fs_info->mapping_tree;
		write_lock(&em_tree->lock);
		remove_extent_mapping(em_tree, em);
		write_unlock(&em_tree->lock);
		/* once for the tree */
		free_extent_map(em);
	}

out:
	/* Once for the lookup reference */
	btrfs_put_block_group(block_group);
	if (remove_rsv)
		btrfs_delayed_refs_rsv_release(fs_info, 1);
	btrfs_free_path(path);
	return ret;
}