Re: [PATCH v1 2/2] xfs: Fix in xfs_rtalloc_query_range()

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

On Wed, Jan 28, 2026 at 08:44:35PM +0530, Nirjhar Roy (IBM) wrote:
> xfs_rtalloc_query_range() should not return 0 by doing a NOP when
> start == end i.e, when the rtgroup size is 1. This causes incorrect
> calculation of free rtextents i.e, the count is reduced by 1 since
> the last rtgroup's rtextent count is not taken and hence xfs_scrub
> throws false summary counter report (from xchk_fscounters()).
> 
> A simple way to reproduce the above bug:
> 
> $ mkfs.xfs -f -m metadir=1 \
> 	-r rtdev=/dev/loop2,extsize=4096,rgcount=4,size=1G \
> 	-d size=1G /dev/loop1
> meta-data=/dev/loop1             isize=512    agcount=4, agsize=65536 blks
>          =                       sectsz=512   attr=2, projid32bit=1
>          =                       crc=1        finobt=1, sparse=1, rmapbt=1
>          =                       reflink=0    bigtime=1 inobtcount=1 nrext64=1
>          =                       exchange=1   metadir=1
> data     =                       bsize=4096   blocks=262144, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0, ftype=1, parent=0
> log      =internal log           bsize=4096   blocks=16384, version=2
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> realtime =/dev/loop2             extsz=4096   blocks=262144, rtextents=262144
>          =                       rgcount=4    rgsize=65536 extents
>          =                       zoned=0      start=0 reserved=0
> Discarding blocks...Done.
> Discarding blocks...Done.
> $ mount -o rtdev=/dev/loop2 /dev/loop1 /mnt1/scratch
> $ xfs_growfs -R $(( 65536 * 4 + 1 ))  /mnt1/scratch
> meta-data=/dev/loop1             isize=512    agcount=4, agsize=65536 blks
>          =                       sectsz=512   attr=2, projid32bit=1
>          =                       crc=1        finobt=1, sparse=1, rmapbt=1
>          =                       reflink=0    bigtime=1 inobtcount=1 nrext64=1
>          =                       exchange=1   metadir=1
> data     =                       bsize=4096   blocks=262144, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0, ftype=1, parent=0
> log      =internal log           bsize=4096   blocks=16384, version=2
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> realtime =/dev/loop2             extsz=4096   blocks=262144, rtextents=262144
>          =                       rgcount=4    rgsize=65536 extents
>          =                       zoned=0      start=0 reserved=0
> calling xfsctl with in.newblocks = 262145
> realtime blocks changed from 262144 to 262145
> $ xfs_scrub -n   -v /mnt1/scratch
> Phase 1: Find filesystem geometry.
> /mnt1/scratch: using 2 threads to scrub.
> Phase 2: Check internal metadata.
> Corruption: rtgroup 4 realtime summary: Repairs are required.
> Phase 3: Scan all inodes.
> Phase 5: Check directory tree.
> Info: /mnt1/scratch: Filesystem has errors, skipping connectivity checks.
> Phase 7: Check summary counters.
> Corruption: filesystem summary counters: Repairs are required.
> 125.0MiB data used;  8.0KiB realtime data used;  15 inodes used.
> 64.3MiB data found; 4.0KiB realtime data found; 18 inodes found.
> 18 inodes counted; 18 inodes checked.
> Phase 8: Trim filesystem storage.
> /mnt1/scratch: corruptions found: 2
> /mnt1/scratch: Re-run xfs_scrub without -n.
> 
> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>

Yeah, that looks right.  I can also reproduce it with:

# mkfs.xfs -m metadir=1 -r rtdev=/dev/sdb /dev/sda -r rgsize=65536b,size=131073b -f
# mount /dev/sda /mnt -o rtdev=/dev/sdb
# xfs_scrub -dTvn /mnt

Cc: <stable@vger.kernel.org> # v6.13
Fixes: e3088ae2dcae3c ("xfs: move RT bitmap and summary information to the rtgroup")

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D
> ---
>  fs/xfs/libxfs/xfs_rtbitmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c
> index 618061d898d4..8f552129ffcc 100644
> --- a/fs/xfs/libxfs/xfs_rtbitmap.c
> +++ b/fs/xfs/libxfs/xfs_rtbitmap.c
> @@ -1170,7 +1170,7 @@ xfs_rtalloc_query_range(
>  
>  	if (start > end)
>  		return -EINVAL;
> -	if (start == end || start >= rtg->rtg_extents)
> +	if (start >= rtg->rtg_extents)
>  		return 0;
>  
>  	end = min(end, rtg->rtg_extents - 1);
> -- 
> 2.43.5
>