The aggregation interval of test purpose damon_attrs for damon_test_nr_accesses_to_accesses_bp() becomes zero on 32 bit architecture, since size of int and long types are same. As a result, damon_nr_accesses_to_accesses_bp() call with the test data triggers divide-by-zero exception. damon_nr_accesses_to_accesses_bp() shouldn't be called with such data, and the non-test code avoids that by checking the case on damon_update_monitoring_results(). Skip the test code in the case, and add an explicit caution of the case on the comment for the test target function.
Reported-by: Guenter Roeck linux@roeck-us.net Closes: https://lore.kernel.org/c771b962-a58f-435b-89e4-1211a9323181@roeck-us.net Fixes: 5e06ad590096 ("mm/damon/core-test: test max_nr_accesses overflow caused divide-by-zero") Signed-off-by: SeongJae Park sj@kernel.org --- mm/damon/core.c | 8 +++++++- mm/damon/tests/core-kunit.h | 12 ++++++++++++ 2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c index 8b99c5a99c38..a83f3b736d51 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -552,7 +552,13 @@ static unsigned int damon_accesses_bp_to_nr_accesses( return accesses_bp * damon_max_nr_accesses(attrs) / 10000; }
-/* convert nr_accesses to access ratio in bp (per 10,000) */ +/* + * Convert nr_accesses to access ratio in bp (per 10,000). + * + * Callers should ensure attrs.aggr_interval is not zero, like + * damon_update_monitoring_results() does . Otherwise, divide-by-zero would + * happen. + */ static unsigned int damon_nr_accesses_to_accesses_bp( unsigned int nr_accesses, struct damon_attrs *attrs) { diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h index ae03df71737e..cf22e09a3507 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -320,6 +320,18 @@ static void damon_test_nr_accesses_to_accesses_bp(struct kunit *test) .aggr_interval = ((unsigned long)UINT_MAX + 1) * 10 };
+ /* + * In some cases such as 32bit architectures where UINT_MAX is + * ULONG_MAX, attrs.aggr_interval becomes zero. Calling + * damon_nr_accesses_to_accesses_bp() in the case will cause + * divide-by-zero. Such case is prohibited in normal execution since + * the caution is documented on the comment for the function, and + * damon_update_monitoring_results() does the check. Skip the test in + * the case. + */ + if (!attrs.aggr_interval) + kunit_skip(test, "aggr_interval is zero."); + KUNIT_EXPECT_EQ(test, damon_nr_accesses_to_accesses_bp(123, &attrs), 0); }