Re: [PATCH] btrfs: fix zoned sub_group leak on space_info sysfs failure

["Naohiro Aota" <Naohiro.Aota@wdc.com>]

On Thu Jun 4, 2026 at 9:10 PM JST, Guangshuo Li wrote:
> On zoned filesystems, create_space_info() creates a space_info sub_group
> before registering the parent space_info in sysfs.
>
> If the sub_group registration succeeds but the parent
> btrfs_sysfs_add_space_info_type() call fails, the parent space_info is
> released through its kobject release path, but the already published
> sub_group is left behind. The sub_group also keeps its logical parent
> pointer, which then points at freed memory.
>
> Remember the created sub_group before registering the parent and remove it
> when parent sysfs registration fails. Cache the sub_group pointer before
> calling btrfs_sysfs_add_space_info_type(), as that helper may already have
> put and released the parent on failure.

Thank you for the patch. The logic itself is correct, but I think there
is a better alternative. My suggestion is making
btrfs_sysfs_remove_space_info() responsible for removing sub-groups (if
any) first.

With that change, we can reverse the space-info creation order in
create_space_info(). If the parent space-info registration fails, no
sub-groups exist yet, so nothing extra needs to be cleaned up. If
sub-group creation fails, we can call btrfs_sysfs_remove_space_info() on
the parent to clean everything up.

This change also has a side benefit. Currently,
check_removing_space_info() is also removing sub-groups, which
contradicts its name. We can remove those
btrfs_sysfs_remove_space_info() calls for sub-groups from the function,
making it a pure checker.

>
> Fixes: f92ee31e031c7 ("btrfs: introduce btrfs_space_info sub-group")
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
> ---
>  fs/btrfs/space-info.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
> index f0436eea1544..03659dfcb830 100644
> --- a/fs/btrfs/space-info.c
> +++ b/fs/btrfs/space-info.c
> @@ -296,6 +296,7 @@ static int create_space_info(struct btrfs_fs_info *info, u64 flags)
>  {
>  
>  	struct btrfs_space_info *space_info;
> +	struct btrfs_space_info *sub_group = NULL;
>  	int ret = 0;
>  
>  	space_info = kzalloc_obj(*space_info, GFP_NOFS);
> @@ -316,11 +317,15 @@ static int create_space_info(struct btrfs_fs_info *info, u64 flags)
>  
>  		if (ret)
>  			goto out_free;
> +		sub_group = space_info->sub_group[0];
>  	}
>  
>  	ret = btrfs_sysfs_add_space_info_type(space_info);
> -	if (ret)
> +	if (ret) {
> +		if (sub_group)
> +			btrfs_sysfs_remove_space_info(sub_group);
>  		return ret;
> +	}
>  
>  	list_add(&space_info->list, &info->space_info);
>  	if (flags & BTRFS_BLOCK_GROUP_DATA)