[PATCH] selftests: cgroup: fix test_kmem_basic false positives

From: Johannes Weiner
Date: Tue Aug 01 2023 - 09:56:45 EST

This test fails routinely in our prod testing environment, and I can
reproduce it locally as well.

The test allocates dcache inside a cgroup, then drops the memory limit
and checks that usage drops correspondingly. The reason it fails is
because dentries are freed with an RCU delay - a debugging sleep shows
that usage drops as expected shortly after.

Insert a 1s sleep after dropping the limit. This should be good
enough, assuming that machines running those tests are otherwise not
very busy.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
tools/testing/selftests/cgroup/test_kmem.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 258ddc565deb..1b2cec9d18a4 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -70,6 +70,10 @@ static int test_kmem_basic(const char *root)
goto cleanup;

cg_write(cg, "memory.high", "1M");
+ /* wait for RCU freeing */
+ sleep(1);
slab1 = cg_read_key_long(cg, "memory.stat", "slab ");
if (slab1 <= 0)
goto cleanup;