Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Roman Gushchin <roman.gushchin@linux.dev>,
        Michal Hocko <mhocko@suse.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] selftests: cgroup: fix test_kmem_basic false positives
Date:   Tue,  1 Aug 2023 09:56:32 -0400
Message-ID: <20230801135632.1768830-1-hannes@cmpxchg.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@cmpxchg.org>
---
 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;
-- 
2.41.0