+ mm-damon-core-avoid-divide-by-zero-from-pseudo-moving-window-length-calculation.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/damon/core: avoid divide-by-zero from pseudo-moving window length calculation
has been added to the -mm mm-unstable branch.  Its filename is
     mm-damon-core-avoid-divide-by-zero-from-pseudo-moving-window-length-calculation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-avoid-divide-by-zero-from-pseudo-moving-window-length-calculation.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: SeongJae Park <sj@kernel.org>
Subject: mm/damon/core: avoid divide-by-zero from pseudo-moving window length calculation
Date: Thu, 19 Oct 2023 19:49:24 +0000

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")
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/damon/core.c~mm-damon-core-avoid-divide-by-zero-from-pseudo-moving-window-length-calculation
+++ a/mm/damon/core.c
@@ -1665,7 +1665,7 @@ void damon_update_region_access_rate(str
 	 * 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);
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-implement-a-function-for-max-nr_accesses-safe-calculation.patch
mm-damon-core-avoid-divide-by-zero-during-monitoring-results-update.patch
mm-damon-ops-common-avoid-divide-by-zero-during-region-hotness-calculation.patch
mm-damon-lru_sort-avoid-divide-by-zero-in-hot-threshold-calculation.patch
mm-damon-core-avoid-divide-by-zero-from-pseudo-moving-window-length-calculation.patch