mm/damon/core: avoid divide-by-zero during monitoring results update

When monitoring attributes are changed, DAMON updates access rate of the
monitoring results accordingly.  For that, it 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/20231019194924.100347-3-sj@kernel.org
Fixes: 2f5bef5a590b ("mm/damon/core: update monitoring results for new monitoring attributes")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Jakub Acs <acsjakub@amazon.de>
Cc: <stable@vger.kernel.org>	[6.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 9f4f7c3..e194c80 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -500,20 +500,14 @@ static unsigned int damon_age_for_new_attrs(unsigned int age,
 static unsigned int damon_accesses_bp_to_nr_accesses(
                unsigned int accesses_bp, struct damon_attrs *attrs)
 {
-       unsigned int max_nr_accesses =
-               attrs->aggr_interval / attrs->sample_interval;
-
-       return accesses_bp * max_nr_accesses / 10000;
+       return accesses_bp * damon_max_nr_accesses(attrs) / 10000;
 }
 
 /* convert nr_accesses to access ratio in bp (per 10,000) */
 static unsigned int damon_nr_accesses_to_accesses_bp(
                unsigned int nr_accesses, struct damon_attrs *attrs)
 {
-       unsigned int max_nr_accesses =
-               attrs->aggr_interval / attrs->sample_interval;
-
-       return nr_accesses * 10000 / max_nr_accesses;
+       return nr_accesses * 10000 / damon_max_nr_accesses(attrs);
 }
 
 static unsigned int damon_nr_accesses_for_new_attrs(unsigned int nr_accesses,