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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
Subject: [PATCH 5/5] mm/damon/core: avoid divide-by-zero from pseudo-moving window length calculation
Date:   Thu, 19 Oct 2023 19:49:24 +0000
Message-Id: <20231019194924.100347-6-sj@kernel.org>
In-Reply-To: <20231019194924.100347-1-sj@kernel.org>
References: <20231019194924.100347-1-sj@kernel.org>
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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.

Fixes: ace30fb21af5 ("mm/damon/core: use pseudo-moving sum for nr_accesses_bp")
Signed-off-by: SeongJae Park <sj@kernel.org>
---

Note that this is for a patch in mm-stable that not yet merged into the
mainline.

 mm/damon/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index e194c8075235..aa2dc7087cd9 100644
--- 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);
-- 
2.34.1