[PATCH 6.1.y] xfs: rescan the AGs if incore delalloc counter is negative

[Sasha Levin <sashal@kernel.org>]

From: "Darrick J. Wong" <djwong@kernel.org>

[ Upstream commit 47b1e941bb55f735d82ba2649412260da78b98f8 ]

LOLLM complains that percpu_counter_sum can return a negative number but
we instead misinterpret that into a huge unsigned value and do bad
things to fdblocks.  It shouldn't do that, so let's add a retry loop and
an attempt to freeze the filesystem to (hopefully) zero out the incore
delalloc counter.  It probably won't work, but at least failing the
repair beats doing the wrong thing.

Cc: stable@vger.kernel.org # v5.2
Fixes: 75efa57d0bf5fc ("xfs: add online scrub for superblock counters")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
[ sashal: omitted the changes to xchk_fscount_count_frextents() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/xfs/scrub/fscounters.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c
index 88d6961e38866..1f4170bab6908 100644
--- a/fs/xfs/scrub/fscounters.c
+++ b/fs/xfs/scrub/fscounters.c
@@ -173,7 +173,7 @@ xchk_fscount_aggregate_agcounts(
 {
 	struct xfs_mount	*mp = sc->mp;
 	struct xfs_perag	*pag;
-	uint64_t		delayed;
+	int64_t			delayed;
 	xfs_agnumber_t		agno;
 	int			tries = 8;
 	int			error = 0;
@@ -233,6 +233,11 @@ xchk_fscount_aggregate_agcounts(
 	 * of the computation.
 	 */
 	delayed = percpu_counter_sum(&mp->m_delalloc_blks);
+	if (delayed < 0) {
+		ASSERT(delayed >= 0);
+		xchk_set_incomplete(sc);
+		return -EFSCORRUPTED;
+	}
 	fsc->fdblocks -= delayed;
 
 	trace_xchk_fscounters_calc(mp, fsc->icount, fsc->ifree, fsc->fdblocks,
-- 
2.53.0