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/[email protected]
Fixes: 198f0f4 ("mm/damon/vaddr,paddr: support pageout prioritization")
Signed-off-by: SeongJae Park <[email protected]>
Reported-by: Jakub Acs <[email protected]>
Cc: <[email protected]>	[5.16+]
Signed-off-by: Andrew Morton <[email protected]>

Author: sjp38

mm/damon/ops-common.c

@@ -73,16 +73,15 @@ 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;
 	unsigned int freq_weight = s->quota.weight_nr_accesses;
 	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;