damon_split_region_at() should be called with the correct address to
split on.  Add a sanity check for that under CONFIG_DAMON_DEBUG_SANITY.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 93d1577b1ae07..be2300cf3aeae 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2586,6 +2586,21 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,
 			threshold / 2 < max_thres);
 }
 
+#ifdef CONFIG_DAMON_DEBUG_SANITY
+static void damon_verify_split_region_at(struct damon_region *r,
+		unsigned long sz_r)
+{
+	WARN_ONCE(sz_r == 0 || sz_r >= damon_sz_region(r),
+			"sz_r: %lu r: %lu-%lu (%lu)\n",
+			sz_r, r->ar.start, r->ar.end, damon_sz_region(r));
+}
+#else
+static void damon_verify_split_region_at(struct damon_region *r,
+		unsigned long sz_r)
+{
+}
+#endif
+
 /*
  * Split a region in two
  *
@@ -2597,6 +2612,7 @@ static void damon_split_region_at(struct damon_target *t,
 {
 	struct damon_region *new;
 
+	damon_verify_split_region_at(r, sz_r);
 	new = damon_new_region(r->ar.start + sz_r, r->ar.end);
 	if (!new)
 		return;
-- 
2.47.3