FAILED: patch "[PATCH] xfs: rescan the AGs if incore delalloc counter is negative" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 47b1e941bb55f735d82ba2649412260da78b98f8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110409-willow-coastline-1f7d@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 47b1e941bb55f735d82ba2649412260da78b98f8 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <[email protected]>
Date: Mon, 12 Oct 2026 23:09:07 -0700
Subject: [PATCH] xfs: rescan the AGs if incore delalloc counter is negative

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.

index 5984fe13a973..67e159f39951 100644
@@ -297,7 +297,7 @@ xchk_fscount_aggregate_agcounts(
 {
 	struct xfs_mount	*mp = sc->mp;
 	struct xfs_perag	*pag = NULL;
-	uint64_t		delayed;
+	int64_t			delayed;
 	int			tries = 8;
 	int			error = 0;
 

@@ -359,6 +359,11 @@ 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,

@@ -417,6 +422,7 @@ xchk_fscount_count_frextents(
 {
 	struct xfs_mount	*mp = sc->mp;
 	struct xfs_rtgroup	*rtg = NULL;
+	int64_t			delayed;
 	int			error;
 
 	fsc->frextents = 0;

@@ -442,7 +448,14 @@ xchk_fscount_count_frextents(
 		}
 	}
 
-	fsc->frextents_delayed = percpu_counter_sum(&mp->m_delalloc_rtextents);
+	delayed = percpu_counter_sum(&mp->m_delalloc_rtextents);
+	if (delayed < 0) {
+		ASSERT(delayed >= 0);
+		xchk_set_incomplete(sc);
+		return -EFSCORRUPTED;
+	}
+	fsc->frextents_delayed = delayed;
+
 	return 0;
 }
 #else

From: "Darrick J. Wong" <[email protected]>

[ 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.

---
 fs/xfs/scrub/fscounters.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

index 037541339d80a..f17912a9cda8d 100644
@@ -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