Re: [PATCH] btrfs: set space_info before adding new free space in btrfs_make_block_group()

[Boris Burkov <boris@bur.io>]

On Mon, Aug 24, 2026 at 06:47:58PM +0200, Johannes Thumshirn wrote:
> btrfs_make_block_group() calls btrfs_add_new_free_space() before
> assigning cache->space_info. On a zoned filesystem that ends up in
> __btrfs_add_free_space_zoned(), which dereferences
> block_group->space_info and thus hits a NULL pointer dereference when a
> non-initial free space range is added (e.g. during relocation).
> 
> Assign cache->space_info before the btrfs_add_new_free_space() call.
> 
Reviewed-by: Boris Burkov <boris@bur.io>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  fs/btrfs/block-group.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 830460a40e86..ee182369254c 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -3074,21 +3074,25 @@ struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *tran
>  		return ERR_PTR(ret);
>  	}
>  
> -	ret = btrfs_add_new_free_space(cache, chunk_offset, chunk_offset + size, NULL);
> -	btrfs_free_excluded_extents(cache);
> -	if (ret) {
> -		btrfs_put_block_group(cache);
> -		return ERR_PTR(ret);
> -	}
> -
>  	/*
>  	 * Ensure the corresponding space_info object is created and
>  	 * assigned to our block group. We want our bg to be added to the rbtree
>  	 * with its ->space_info set.
> +	 *
> +	 * On a zoned filesystem btrfs_add_new_free_space() ends up in
> +	 * __btrfs_add_free_space_zoned(), which dereferences
> +	 * block_group->space_info, so it has to be set beforehand.
>  	 */
>  	cache->space_info = space_info;
>  	ASSERT(cache->space_info);
>  
> +	ret = btrfs_add_new_free_space(cache, chunk_offset, chunk_offset + size, NULL);
> +	btrfs_free_excluded_extents(cache);
> +	if (ret) {
> +		btrfs_put_block_group(cache);
> +		return ERR_PTR(ret);
> +	}
> +
>  	ret = btrfs_add_block_group_cache(cache);
>  	if (ret) {
>  		btrfs_remove_free_space_cache(cache);
> -- 
> 2.55.0
>