In test_no_kmem_bypass(), delta (stored_pages * page_size - zswapped) is
checked against stored_pages * page_size / 4 to verify that the pages
pushed to zswap belong to the test memory cgroup.
Due to slight stat update timing differences, delta can evaluate to a small
negative number (e.g. -5MB out of 1GB). Because delta is declared as a
signed int and stored_pages is an unsigned size_t, C's usual arithmetic
conversions implicitly promote a negative delta to a large unsigned 64-bit
integer, causing `delta < stored_pages * page_size / 4` to falsely evaluate
to 0 and fail the test.
Fix this by declaring zswapped and delta as signed long long and comparing
against a signed threshold, ensuring negative deltas correctly evaluate
to true.
Fixes: a549f9f31561a ("selftests: cgroup: add test_zswap with no kmem bypass
test")
Signed-off-by: Wilson Felipe Pereira <[email protected]>
Acked-by: Michal Koutný <[email protected]>
---
tools/testing/selftests/cgroup/test_zswap.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c
b/tools/testing/selftests/cgroup/test_zswap.c
index 1d3c410252e4..2e7d123e0949 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -630,11 +630,14 @@ static int test_no_kmem_bypass(const char *root)
break;
/* If memory was pushed to zswap, verify it belongs to memcg */
if (stored_pages > stored_pages_threshold) {
- int zswapped = cg_read_key_long(test_group,
"memory.stat", "zswapped ");
- int delta = stored_pages * page_size - zswapped;
- int result_ok = delta < stored_pages * page_size / 4;
-
- ret = result_ok ? KSFT_PASS : KSFT_FAIL;
+ long zswapped = cg_read_key_long(
+ test_group, "memory.stat", "zswapped ");
+ long long delta =
+ (long long)stored_pages * page_size - zswapped;
+ long long max_delta =
+ (long long)stored_pages * page_size / 4;
+
+ ret = (delta < max_delta) ? KSFT_PASS : KSFT_FAIL;
break;
}
}
--
2.55.0.897.gb25b4bd76c-goog
