From: Darrick J. Wong djwong@kernel.org
commit 1aacd3fac248902ea1f7607f2d12b93929a4833b upstream
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: stable@vger.kernel.org # v6.13-rc3 Fixes: ca378189fdfa89 ("xfs: convert quotacheck to attach dquot buffers") Signed-off-by: "Darrick J. Wong" djwong@kernel.org Reviewed-by: Christoph Hellwig hch@lst.de --- 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 d2b06ca2ec7a9c..d64d454cbe8bca 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -1308,7 +1308,8 @@ 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( @@ -1329,13 +1330,16 @@ 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);