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...

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/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@kernel.org Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization") Signed-off-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org [5.16+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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@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