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[3/5] mm/damon/ops-common: avoid divide-by-zero during region hotness calculation

Message ID 20231019194924.100347-4-sj@kernel.org (mailing list archive)
State New
Headers show
Series avoid divide-by-zero due to max_nr_accesses overflow | expand

Commit Message

SeongJae Park Oct. 19, 2023, 7:49 p.m. UTC 
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.

Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization")
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/ops-common.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
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Patch

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index ac1c3fa80f98..d25d99cb5f2b 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -73,7 +73,6 @@  void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr
 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, struct damon_region *r,
 	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;