linux-kernel - [PATCH v2 4/5] mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation

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Message-Id: <20231020172317.64192-5-sj@kernel.org>
Date:   Fri, 20 Oct 2023 17:23:16 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     SeongJae Park <sj@...nel.org>, Jakub Acs <acsjakub@...zon.de>,
        damon@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH v2 4/5] mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation

When calculating the hotness threshold for lru_prio scheme of
DAMON_LRU_SORT, the module 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.

Reported-by: Jakub Acs <acsjakub@...zon.de>
Fixes: 40e983cca927 ("mm/damon: introduce DAMON-based LRU-lists Sorting")
Cc: <stable@...r.kernel.org> # 6.0.x
Signed-off-by: SeongJae Park <sj@...nel.org>
---
 mm/damon/lru_sort.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 3ecdcc029443..f2e5f9431892 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -195,9 +195,7 @@ static int damon_lru_sort_apply_parameters(void)
 	if (err)
 		return err;
 
-	/* aggr_interval / sample_interval is the maximum nr_accesses */
-	hot_thres = damon_lru_sort_mon_attrs.aggr_interval /
-		damon_lru_sort_mon_attrs.sample_interval *
+	hot_thres = damon_max_nr_accesses(&damon_lru_sort_mon_attrs) *
 		hot_thres_access_freq / 1000;
 	scheme = damon_lru_sort_new_hot_scheme(hot_thres);
 	if (!scheme)
-- 
2.34.1