[PATCH 1/3] mm/damon: do not allow creating zero size region

[Honggyu Kim <honggyu.kim@sk.com>]

Creating zero size region leads a divide by zero error inside
damon_get_intervals_score() as follows.

  static unsigned long damon_get_intervals_score(struct damon_ctx *c)
  {
      struct damon_target *t;
      struct damon_region *r;
      unsigned long sz_region, max_access_events = 0, access_events = 0;
      unsigned long target_access_events;
      unsigned long goal_bp = c->attrs.intervals_goal.access_bp;

      damon_for_each_target(t, c) {
          damon_for_each_region(r, t) {
              sz_region = damon_sz_region(r);
              max_access_events += sz_region * c->attrs.aggr_samples;
              access_events += sz_region * r->nr_accesses;
          }
      }
      target_access_events = max_access_events * goal_bp / 10000;
      return access_events * 10000 / target_access_events;  /* divide by zero! */
  }

This patch makes a NULL return for such cases when creating a region
inside damon_new_region().

Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Cc: Yunjeong Mun <yunjeong.mun@sk.com>
---
 mm/damon/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index b217e0120e09..44740da337fd 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -126,8 +126,11 @@ struct damon_region *damon_new_region(unsigned long start, unsigned long end)
 	if (!region)
 		return NULL;
 
+	if (start == end)
+		return NULL;
 	region->ar.start = start;
 	region->ar.end = end;
+
 	region->nr_accesses = 0;
 	region->nr_accesses_bp = 0;
 	INIT_LIST_HEAD(&region->list);
-- 
2.34.1