damon_target->nr_regions is introduced to get the number quickly without
having to iterate regions always.  Add a sanity check for that under
CONFIG_DAMON_DEBUG_SANITY.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 92eac5eb96026..2b5aed89d449d 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -545,8 +545,27 @@ void damon_destroy_target(struct damon_target *t, struct damon_ctx *ctx)
 	damon_free_target(t);
 }
 
+#ifdef CONFIG_DAMON_DEBUG_SANITY
+static void damon_verify_nr_regions(struct damon_target *t)
+{
+	struct damon_region *r;
+	unsigned int count = 0;
+
+	damon_for_each_region(r, t)
+		count++;
+	WARN_ONCE(count != t->nr_regions, "t->nr_regions (%u) != count (%u)\n",
+			t->nr_regions, count);
+}
+#else
+static void damon_verify_nr_regions(struct damon_target *t)
+{
+}
+#endif
+
 unsigned int damon_nr_regions(struct damon_target *t)
 {
+	damon_verify_nr_regions(t);
+
 	return t->nr_regions;
 }
 
-- 
2.47.3