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From:   SeongJae Park <sj@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     SeongJae Park <sj@kernel.org>, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: [PATCH 2/5] mm/damon/core: avoid divide-by-zero during monitoring results update
Date:   Thu, 19 Oct 2023 19:49:21 +0000
Message-Id: <20231019194924.100347-3-sj@kernel.org>
In-Reply-To: <20231019194924.100347-1-sj@kernel.org>
References: <20231019194924.100347-1-sj@kernel.org>
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When monitoring attributes are changed, DAMON updates access rate of the
monitoring results accordingly.  For that, it 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.

Fixes: 2f5bef5a590b ("mm/damon/core: update monitoring results for new monitoring attributes")
Cc: <stable@vger.kernel.org> # 6.3.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 9f4f7c378cf3..e194c8075235 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -500,20 +500,14 @@ static unsigned int damon_age_for_new_attrs(unsigned int age,
 static unsigned int damon_accesses_bp_to_nr_accesses(
 		unsigned int accesses_bp, struct damon_attrs *attrs)
 {
-	unsigned int max_nr_accesses =
-		attrs->aggr_interval / attrs->sample_interval;
-
-	return accesses_bp * max_nr_accesses / 10000;
+	return accesses_bp * damon_max_nr_accesses(attrs) / 10000;
 }
 
 /* convert nr_accesses to access ratio in bp (per 10,000) */
 static unsigned int damon_nr_accesses_to_accesses_bp(
 		unsigned int nr_accesses, struct damon_attrs *attrs)
 {
-	unsigned int max_nr_accesses =
-		attrs->aggr_interval / attrs->sample_interval;
-
-	return nr_accesses * 10000 / max_nr_accesses;
+	return nr_accesses * 10000 / damon_max_nr_accesses(attrs);
 }
 
 static unsigned int damon_nr_accesses_for_new_attrs(unsigned int nr_accesses,
-- 
2.34.1