mm/damon/core: avoid divide-by-zero from pseudo-moving window length calculation

When calculating the pseudo-moving access rate, DAMON divides some values
by the maximum nr_accesses.  However, due to the type of the related
variables, simple division-based calculation of the divisor can return
zero.  As a result, divide-by-zero is possible.  Fix it by using
damon_max_nr_accesses(), which handles the case.

Note that this is a fix for a commit that not in the mainline but mm
tree.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: ace30fb ("mm/damon/core: use pseudo-moving sum for nr_accesses_bp")
Reported-by: Jakub Acs <[email protected]>
Signed-off-by: SeongJae Park <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: sjp38

mm/damon/core.c

@@ -1665,7 +1665,7 @@ void damon_update_region_access_rate(struct damon_region *r, bool accessed,
 	 * aggr_interval, owing to validation of damon_set_attrs().
 	 */
 	if (attrs->sample_interval)
-		len_window = attrs->aggr_interval / attrs->sample_interval;
+		len_window = damon_max_nr_accesses(attrs);
 	r->nr_accesses_bp = damon_moving_sum(r->nr_accesses_bp,
 			r->last_nr_accesses * 10000, len_window,
 			accessed ? 10000 : 0);