selftests: cgroup: fix test_kmem_basic false positives

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.

Link: https://lkml.kernel.org/r/20230801135632.1768830-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 258ddc565debaaa47f67284bdbccba81ecd5faf0..1b2cec9d18a42b4acdb1208b0d6f1d51bc18a888 100644 (file)
--- 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;