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 longs 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 --- tools/testing/selftests/cgroup/test_zswap.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c index a7ff525c1267..15cc1dfdd1f4 100644 --- a/tools/testing/selftests/cgroup/test_zswap.c +++ b/tools/testing/selftests/cgroup/test_zswap.c @@ -621,9 +621,11 @@ 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; + long zswapped = cg_read_key_long( + test_group, "memory.stat", "zswapped "); + long delta = stored_pages * page_size - zswapped; + long max_delta = (long)(stored_pages * page_size / 4); + int result_ok = delta < max_delta; ret = result_ok ? KSFT_PASS : KSFT_FAIL; break; -- 2.55.0.766.g2966f0265a-goog