mm/damon/core: do not use region out of a loop in damon_set_regions()

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.

Link: https://lore.kernel.org/20260522154026.80546-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 8360cb4c506effc2c7e4517ae854d75950934aca..c9946ac8e2794497ea2eb417ac7ab81a139cc0f0 100644 (file)
--- 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,