+ mm-damon-lru_sort-avoid-divide-by-zero-in-hot-threshold-calculation.patch added to mm-hotfixes-unstable branch

+ mm-damon-lru_sort-avoid-divide-by-zero-in-hot-threshold-calculation.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-damon-lru_sort-avoid-divide-by-zero-in-hot-threshold-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-lru_sort-avoid-divide-by-zero-in-hot-threshold-calculation.patch

This patch will later appear in the mm-hotfixes-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/lru_sort: avoid divide-by-zero in hot threshold calculation
Date: Thu, 19 Oct 2023 19:49:23 +0000

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.

Link: https://lkml.kernel.org/r/20231019194924.100347-5-sj@kernel.org
Fixes: 40e983cca927 ("mm/damon: introduce DAMON-based LRU-lists Sorting")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.0+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/lru_sort.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/mm/damon/lru_sort.c~mm-damon-lru_sort-avoid-divide-by-zero-in-hot-threshold-calculation
+++ a/mm/damon/lru_sort.c
@@ -193,9 +193,7 @@ static int damon_lru_sort_apply_paramete
 	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)
_

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