[RFC PATCH 02/14] mm/damon/core: do not use region out of a loop in damon_set_regions()

[SeongJae Park <sj@kernel.org>]

damon_set_regions() assumes the DAMON region iterator is referencing the
last region after the region iteration loop is completed.  The code is
indeed implemented in the way, but that is not a documented safe
behavior.  Hence it is unreliable and difficult to read.  Cleanup the
code to avoid the case.

No behavioral change is intended.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 40946a7f6f549..e8cf3632115e5 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -374,6 +374,7 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 	for (i = 0; i < nr_ranges; i++) {
 		struct damon_region *first = NULL, *last, *newr;
 		struct damon_addr_range *range;
+		bool insert_before_r = false;
 
 		range = &ranges[i];
 		/* Get the first/last regions intersecting with the range */
@@ -383,8 +384,10 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 					first = r;
 				last = r;
 			}
-			if (r->ar.start >= range->end)
+			if (r->ar.start >= range->end) {
+				insert_before_r = true;
 				break;
+			}
 		}
 		if (!first) {
 			/* no region intersects with this range */
@@ -394,7 +397,11 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 					ALIGN(range->end, min_region_sz));
 			if (!newr)
 				return -ENOMEM;
-			damon_insert_region(newr, damon_prev_region(r), r, t);
+			if (insert_before_r)
+				damon_insert_region(newr, damon_prev_region(r),
+						r, t);
+			else
+				damon_add_region(newr, t);
 		} else {
 			/* resize intersecting regions to fit in this range */
 			first->ar.start = ALIGN_DOWN(range->start,
-- 
2.47.3