mm/damon/ops-common: avoid divide-by-zero during region hotness calculation

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>
Reported-by: Jakub Acs <acsjakub@amazon.de>
Cc: <stable@vger.kernel.org>	[5.16+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index ac1c3fa80f9847cbae9972b989254a4f58aeb049..d25d99cb5f2bb9a1eead9d555a2d42c9d2b4af45 100644 (file)
--- 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;