Re: [PATCH] xfs: fix overflows when converting from a count of groups to blocks

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Oct 27, 2025 at 03:04:39PM +0100, Christoph Hellwig wrote:
> Add a xfs_group helper and a xfs_rtgroup wrapper and use that to avoid
> overflows when converting zone/rtg counts to block counts.
> 
> Fixes: 0bb2193056b5 ("xfs: add support for zoned space reservations")
> Fixes: 080d01c41d44 ("xfs: implement zoned garbage collection")

Cc: <stable@vger.kernel.org> # v6.15

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_group.h    | 9 +++++++++
>  fs/xfs/libxfs/xfs_rtgroup.h  | 8 ++++++++
>  fs/xfs/xfs_zone_gc.c         | 3 +--
>  fs/xfs/xfs_zone_space_resv.c | 8 +++-----
>  4 files changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_group.h b/fs/xfs/libxfs/xfs_group.h
> index 4423932a2313..a6eabe6da4fb 100644
> --- a/fs/xfs/libxfs/xfs_group.h
> +++ b/fs/xfs/libxfs/xfs_group.h
> @@ -98,6 +98,15 @@ xfs_group_max_blocks(
>  	return xg->xg_mount->m_groups[xg->xg_type].blocks;
>  }
>  
> +static inline xfs_rfsblock_t
> +xfs_groups_to_fsb(

Minor nitpicking: should these functions that return a raw fsblock count
(xfs_rfsblock_t) have a slightly different name?

xfs_groups_to_rfsb() ?

Just so that someone doesn't think the return value is a segmented
fsblock address based on a misreading of the function name...

> +	struct xfs_mount	*mp,
> +	uint32_t		nr_groups,
> +	enum xfs_group_type	type)
> +{
> +	return (xfs_rfsblock_t)mp->m_groups[type].blocks * nr_groups;
> +}
> +
>  static inline xfs_fsblock_t
>  xfs_group_start_fsb(
>  	struct xfs_group	*xg)
> diff --git a/fs/xfs/libxfs/xfs_rtgroup.h b/fs/xfs/libxfs/xfs_rtgroup.h
> index d36a6ae0abe5..a34da969bb6b 100644
> --- a/fs/xfs/libxfs/xfs_rtgroup.h
> +++ b/fs/xfs/libxfs/xfs_rtgroup.h
> @@ -365,4 +365,12 @@ static inline int xfs_initialize_rtgroups(struct xfs_mount *mp,
>  # define xfs_rtgroup_get_geometry(rtg, rgeo)	(-EOPNOTSUPP)
>  #endif /* CONFIG_XFS_RT */
>  
> +static inline xfs_rfsblock_t
> +xfs_rtgs_to_rtb(

...especially since we're really not returning an rtblock here.

The additional casting is correct though.

--D

> +	struct xfs_mount	*mp,
> +	uint32_t		nr_groups)
> +{
> +	return xfs_groups_to_fsb(mp, nr_groups, XG_TYPE_RTG);
> +}
> +
>  #endif /* __LIBXFS_RTGROUP_H */
> diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
> index 109877d9a6bf..c43513531200 100644
> --- a/fs/xfs/xfs_zone_gc.c
> +++ b/fs/xfs/xfs_zone_gc.c
> @@ -179,8 +179,7 @@ xfs_zoned_need_gc(
>  	available = xfs_estimate_freecounter(mp, XC_FREE_RTAVAILABLE);
>  
>  	if (available <
> -	    mp->m_groups[XG_TYPE_RTG].blocks *
> -	    (mp->m_max_open_zones - XFS_OPEN_GC_ZONES))
> +	    xfs_rtgs_to_rtb(mp, mp->m_max_open_zones - XFS_OPEN_GC_ZONES))
>  		return true;
>  
>  	free = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS);
> diff --git a/fs/xfs/xfs_zone_space_resv.c b/fs/xfs/xfs_zone_space_resv.c
> index 9cd38716fd25..3a1a363fc8ea 100644
> --- a/fs/xfs/xfs_zone_space_resv.c
> +++ b/fs/xfs/xfs_zone_space_resv.c
> @@ -54,12 +54,10 @@ xfs_zoned_default_resblks(
>  {
>  	switch (ctr) {
>  	case XC_FREE_RTEXTENTS:
> -		return (uint64_t)XFS_RESERVED_ZONES *
> -			mp->m_groups[XG_TYPE_RTG].blocks +
> -			mp->m_sb.sb_rtreserved;
> +		return xfs_rtgs_to_rtb(mp, XFS_RESERVED_ZONES) +
> +				mp->m_sb.sb_rtreserved;
>  	case XC_FREE_RTAVAILABLE:
> -		return (uint64_t)XFS_GC_ZONES *
> -			mp->m_groups[XG_TYPE_RTG].blocks;
> +		return xfs_rtgs_to_rtb(mp, XFS_GC_ZONES);
>  	default:
>  		ASSERT(0);
>  		return 0;
> -- 
> 2.47.3
> 
>