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/20231019194924.100347-6-sj@kernel.org
Fixes: ace30fb21af5 ("mm/damon/core: use pseudo-moving sum for nr_accesses_bp")
Reported-by: Jakub Acs <acsjakub@amazon.de>
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index e194c80..aa2dc70 100644 (file)
--- a/mm/damon/core.c
+++ b/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);