Re: [PATCH 1/2] btrfs-progs: check: add repair ability for missing orphan root item

[Boris Burkov <boris@bur.io>]

On Sat, Nov 15, 2025 at 08:15:59AM +1030, Qu Wenruo wrote:
> There is a known bug in older kernels that orphan items can be missing
> for dropped subvolumes.
> 
> This makes those subvolumes unable to be removed on the next mount, and
> recent kernel commit 4289b494ac55 ("btrfs: do not allow relocation of
> partially dropped subvolumes") introduced one extra safe net to catch
> such problem.
> 
> But unfortunately there is no way to repair it.
> 
> Add the repair ability to both the original and lowmem modes.
> 
> Link: https://lore.kernel.org/linux-btrfs/01f8b560-fb57-4861-8382-141c39655478@gmx.com/
> Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Boris Burkov <boris@bur.io>
> ---
>  check/main.c        |  5 +++++
>  check/mode-common.c | 33 +++++++++++++++++++++++++++++++++
>  check/mode-common.h |  1 +
>  check/mode-lowmem.c | 13 ++++++++++---
>  4 files changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/check/main.c b/check/main.c
> index 77458a769028..db055ae194f8 100644
> --- a/check/main.c
> +++ b/check/main.c
> @@ -3550,6 +3550,11 @@ static int check_root_refs(struct btrfs_root *root,
>  				 */
>  				if (!rec->found_root_item)
>  					continue;
> +				if (opt_check_repair) {
> +					ret = repair_subvol_orphan_item(gfs_info, rec->objectid);
> +					if (!ret)
> +						continue;
> +				}
>  				errors++;
>  				fprintf(stderr, "fs tree %llu missing orphan item\n", rec->objectid);
>  			}
> diff --git a/check/mode-common.c b/check/mode-common.c
> index 0467ba28395e..2d11a96dfb7e 100644
> --- a/check/mode-common.c
> +++ b/check/mode-common.c
> @@ -1672,3 +1672,36 @@ int check_and_repair_super_num_devs(struct btrfs_fs_info *fs_info)
>  	printf("Successfully reset super num devices to %u\n", found_devs);
>  	return 0;
>  }
> +
> +int repair_subvol_orphan_item(struct btrfs_fs_info *fs_info, u64 rootid)
> +{
> +	struct btrfs_root *tree_root = fs_info->tree_root;
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_path path = { 0 };
> +	int ret;
> +
> +	trans = btrfs_start_transaction(tree_root, 1);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		errno = -ret;
> +		error_msg(ERROR_MSG_START_TRANS, "%m");
> +		return ret;
> +	}
> +	ret = btrfs_add_orphan_item(trans, tree_root, &path, rootid);
> +	btrfs_release_path(&path);
> +	if (ret < 0) {
> +		errno = -ret;
> +		error("failed to insert orphan item for subvolume %llu: %m", rootid);
> +		btrfs_abort_transaction(trans, ret);
> +		btrfs_commit_transaction(trans, tree_root);
> +		return ret;
> +	}
> +	ret = btrfs_commit_transaction(trans, tree_root);
> +	if (ret < 0) {
> +		errno = -ret;
> +		error_msg(ERROR_MSG_COMMIT_TRANS, "%m");
> +		return ret;
> +	}
> +	printf("Added back missing orphan item for subvolume %llu\n", rootid);
> +	return 0;
> +}
> diff --git a/check/mode-common.h b/check/mode-common.h
> index c37b4dc00e54..e97835a5b6a3 100644
> --- a/check/mode-common.h
> +++ b/check/mode-common.h
> @@ -197,5 +197,6 @@ int repair_dev_item_bytes_used(struct btrfs_fs_info *fs_info,
>  int fill_csum_tree(struct btrfs_trans_handle *trans, bool search_fs_tree);
>  
>  int check_and_repair_super_num_devs(struct btrfs_fs_info *fs_info);
> +int repair_subvol_orphan_item(struct btrfs_fs_info *fs_info, u64 rootid);
>  
>  #endif
> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
> index 363dc4ae1904..ea4d4017827f 100644
> --- a/check/mode-lowmem.c
> +++ b/check/mode-lowmem.c
> @@ -5569,9 +5569,16 @@ static int check_btrfs_root(struct btrfs_root *root, int check_all)
>  	 * If this tree is a subvolume (not a reloc tree) and has no refs, there
>  	 * should be an orphan item for it, or this subvolume will never be deleted.
>  	 */
> -	if (btrfs_root_refs(root_item) == 0 && is_fstree(btrfs_root_id(root))) {
> -		if (!has_orphan_item(root->fs_info->tree_root,
> -				     btrfs_root_id(root))) {
> +	if (btrfs_root_refs(root_item) == 0 && is_fstree(btrfs_root_id(root)) &&
> +	    !has_orphan_item(root->fs_info->tree_root, btrfs_root_id(root))) {
> +		bool repaired = false;
> +
> +		if (opt_check_repair) {
> +			ret = repair_subvol_orphan_item(root->fs_info, btrfs_root_id(root));
> +			if (!ret)
> +				repaired = true;
> +		}
> +		if (!repaired) {
>  			error("missing orphan item for root %lld", btrfs_root_id(root));
>  			err |= REFERENCER_MISSING;
>  		}
> -- 
> 2.51.2
>