+ mm-damon-core-avoid-divide-by-zero-during-monitoring-results-update.patch added to mm-hotfixes-unstable branch

+ mm-damon-core-avoid-divide-by-zero-during-monitoring-results-update.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/core: avoid divide-by-zero during monitoring results update
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-damon-core-avoid-divide-by-zero-during-monitoring-results-update.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-during-monitoring-results-update.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/core: avoid divide-by-zero during monitoring results update
Date: Thu, 19 Oct 2023 19:49:21 +0000

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.

Link: https://lkml.kernel.org/r/20231019194924.100347-3-sj@kernel.org
Fixes: 2f5bef5a590b ("mm/damon/core: update monitoring results for new monitoring attributes")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/core.c |   10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

--- a/mm/damon/core.c~mm-damon-core-avoid-divide-by-zero-during-monitoring-results-update
+++ a/mm/damon/core.c
@@ -476,20 +476,14 @@ static unsigned int damon_age_for_new_at
 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,
_

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