The patch titled
Subject: mm/damon/ops-common: avoid divide-by-zero during region hotness calculation
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-damon-ops-common-avoid-divide-by-zero-during-region-hotness-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-ops-common-avoid-divide-by-zero-during-region-hotness-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@xxxxxxxxxx>
Subject: mm/damon/ops-common: avoid divide-by-zero during region hotness calculation
Date: Thu, 19 Oct 2023 19:49:22 +0000
When calculating the hotness of each region for the under-quota regions
prioritization, 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.
Link: https://lkml.kernel.org/r/20231019194924.100347-4-sj@xxxxxxxxxx
Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization")
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.16+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/damon/ops-common.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/mm/damon/ops-common.c~mm-damon-ops-common-avoid-divide-by-zero-during-region-hotness-calculation
+++ a/mm/damon/ops-common.c
@@ -73,7 +73,6 @@ void damon_pmdp_mkold(pmd_t *pmd, struct
int damon_hot_score(struct damon_ctx *c, struct damon_region *r,
struct damos *s)
{
- unsigned int max_nr_accesses;
int freq_subscore;
unsigned int age_in_sec;
int age_in_log, age_subscore;
@@ -81,8 +80,8 @@ int damon_hot_score(struct damon_ctx *c,
unsigned int age_weight = s->quota.weight_age;
int hotness;
- max_nr_accesses = c->attrs.aggr_interval / c->attrs.sample_interval;
- freq_subscore = r->nr_accesses * DAMON_MAX_SUBSCORE / max_nr_accesses;
+ freq_subscore = r->nr_accesses * DAMON_MAX_SUBSCORE /
+ damon_max_nr_accesses(&c->attrs);
age_in_sec = (unsigned long)r->age * c->attrs.aggr_interval / 1000000;
for (age_in_log = 0; age_in_log < DAMON_MAX_AGE_IN_LOG && age_in_sec;
_
Patches currently in -mm which might be from sj@xxxxxxxxxx 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
