From 4b8d867ca6e2fc6d152f629fdaf027053b81765a Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Thu, 12 Dec 2024 14:37:56 -0800 Subject: [PATCH 1/2] xfs: don't over-report free space or inodes in statvfs 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: # v2.6.18 Fixes: 932f2c323196c2 ("[XFS] statvfs component of directory/project quota support, code originally by Glen.") Reported-by: Emmanuel Florac Signed-off-by: "Darrick J. Wong" Reviewed-by: Christoph Hellwig --- 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 847ba29630e9..db5b8afd9d1b 100644 --- a/fs/xfs/xfs_qm_bhv.c +++ b/fs/xfs/xfs_qm_bhv.c @@ -32,21 +32,28 @@ xfs_fill_statvfs_from_dquot( limit = blkres->softlimit ? blkres->softlimit : blkres->hardlimit; - if (limit && statp->f_blocks > limit) { - statp->f_blocks = limit; - statp->f_bfree = statp->f_bavail = - (statp->f_blocks > blkres->reserved) ? - (statp->f_blocks - blkres->reserved) : 0; + if (limit) { + uint64_t remaining = 0; + + if (limit > blkres->reserved) + remaining = limit - blkres->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); } } From 1aacd3fac248902ea1f7607f2d12b93929a4833b Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Tue, 17 Dec 2024 15:00:49 -0800 Subject: [PATCH 2/2] xfs: release the dquot buf outside of qli_lock Lai Yi reported a lockdep complaint about circular locking: Chain exists of: &lp->qli_lock --> &bch->bc_lock --> &l->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&l->lock); lock(&bch->bc_lock); lock(&l->lock); lock(&lp->qli_lock); I /think/ the problem here is that xfs_dquot_attach_buf during quotacheck will release the buffer while it's holding the qli_lock. Because this is a cached buffer, xfs_buf_rele_cached takes b_lock before decrementing b_hold. Other threads have taught lockdep that a locking dependency chain is bp->b_lock -> bch->bc_lock -> l(ru)->lock; and that another chain is l(ru)->lock -> lp->qli_lock. Hence we do not want to take b_lock while holding qli_lock. Reported-by: syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com Cc: # v6.13-rc3 Fixes: ca378189fdfa89 ("xfs: convert quotacheck to attach dquot buffers") Tested-by: syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com Signed-off-by: "Darrick J. Wong" Reviewed-by: Christoph Hellwig --- fs/xfs/xfs_dquot.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index f11d475898f2..576b7755b1f1 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -1315,7 +1315,8 @@ xfs_dquot_read_buf( /* * Attach a dquot buffer to this dquot to avoid allocating a buffer during a - * dqflush, since dqflush can be called from reclaim context. + * dqflush, since dqflush can be called from reclaim context. Caller must hold + * the dqlock. */ int xfs_dquot_attach_buf( @@ -1336,13 +1337,16 @@ xfs_dquot_attach_buf( return error; /* - * Attach the dquot to the buffer so that the AIL does not have - * to read the dquot buffer to push this item. + * Hold the dquot buffer so that we retain our ref to it after + * detaching it from the transaction, then give that ref to the + * dquot log item so that the AIL does not have to read the + * dquot buffer to push this item. */ xfs_buf_hold(bp); + xfs_trans_brelse(tp, bp); + spin_lock(&qlip->qli_lock); lip->li_buf = bp; - xfs_trans_brelse(tp, bp); } qlip->qli_dirty = true; spin_unlock(&qlip->qli_lock);