[PATCH 08/10] xfs: don't over-report free space or inodes in statvfs

Darrick J. Wong
2025-02-04T18:53:11Z

commit 4b8d867ca6e2fc6d152f629fdaf027053b81765a upstream

Emmanual Florac reports a strange occurrence when project quota limits
are enabled, free space is lower than the remaining quota, and someone
runs statvfs:

# mkfs.xfs -f /dev/sda
# mount /dev/sda /mnt -o prjquota
# xfs_quota -x -c 'limit -p bhard=2G 55' /mnt
# mkdir /mnt/dir
# xfs_io -c 'chproj 55' -c 'chattr +P' -c 'stat -vvvv' /mnt/dir
# fallocate -l 19g /mnt/a
# df /mnt /mnt/dir
Filesystem Size Used Avail Use% Mounted on
/dev/sda 20G 20G 345M 99% /mnt
/dev/sda 2.0G 0 2.0G 0% /mnt

I think the bug here is that xfs_fill_statvfs_from_dquot unconditionally
assigns to f_bfree without checking that the filesystem has enough free
space to fill the remaining project quota. However, this is a
longstanding behavior of xfs so it's unclear what to do here.

Cc: <stable@vger.kernel.org> # v2.6.18
Fixes: 932f2c323196c2 ("[XFS] statvfs component of directory/project quota support, code originally by Glen.")
Reported-by: Emmanuel Florac <eflorac@intellique.com>
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/xfs_qm_bhv.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_qm_bhv.c b/fs/xfs/xfs_qm_bhv.c
index a11436579877d5..410a2a9c18ec52 100644
--- a/fs/xfs/xfs_qm_bhv.c
+++ b/fs/xfs/xfs_qm_bhv.c
@@ -26,21 +26,28 @@ xfs_fill_statvfs_from_dquot(
limit = dqp->q_blk.softlimit ?
dqp->q_blk.softlimit :
dqp->q_blk.hardlimit;
- if (limit && statp->f_blocks > limit) {
- statp->f_blocks = limit;
- statp->f_bfree = statp->f_bavail =
- (statp->f_blocks > dqp->q_blk.reserved) ?
- (statp->f_blocks - dqp->q_blk.reserved) : 0;
+ if (limit) {
+ uint64_t remaining = 0;
+
+ if (limit > dqp->q_blk.reserved)
+ remaining = limit - dqp->q_blk.reserved;
+
+ statp->f_blocks = min(statp->f_blocks, limit);
+ statp->f_bfree = min(statp->f_bfree, remaining);
+ statp->f_bavail = min(statp->f_bavail, remaining);
}

limit = dqp->q_ino.softlimit ?
dqp->q_ino.softlimit :
dqp->q_ino.hardlimit;
- if (limit && statp->f_files > limit) {
- statp->f_files = limit;
- statp->f_ffree =
- (statp->f_files > dqp->q_ino.reserved) ?
- (statp->f_files - dqp->q_ino.reserved) : 0;
+ if (limit) {
+ uint64_t remaining = 0;
+
+ if (limit > dqp->q_ino.reserved)
+ remaining = limit - dqp->q_ino.reserved;
+
+ statp->f_files = min(statp->f_files, limit);
+ statp->f_ffree = min(statp->f_ffree, remaining);
}
}