linux-kernel - [PATCH v8 1/2] selftests: memcg: Allow low event with no memory.low and memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250502010443.106022-2-longman@redhat.com>
Date: Thu,  1 May 2025 21:04:42 -0400
From: Waiman Long <longman@...hat.com>
To: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org,
	Waiman Long <longman@...hat.com>
Subject: [PATCH v8 1/2] selftests: memcg: Allow low event with no memory.low and memory_recursiveprot on

The test_memcontrol selftest consistently fails its test_memcg_low
sub-test due to the fact that its 3rd test child cgroup which
have a memmory.low of 0 have low event count. This happens when
memory_recursiveprot mount option is enabled which is the default
setting used by systemd to mount cgroup2 filesystem.

This issue was originally fixed by commit cdc69458a5f3 ("cgroup:
account for memory_recursiveprot in test_memcg_low()"). It was later
reverted by commit 1d09069f5313 ("selftests: memcg: expect no low events
in unprotected sibling") expecting the memory reclaim code would be
fixed. However, it turns out the unprotected cgroup may still have some
residual effective memory.low protection depending on the memory.low
settings in its parent and its siblings. As a result, low events may
still be triggered.

One way to fix the test failure is to revert the revert commit. However,
Michal suggested that it might be better to ignore the low event count
with memory_recursiveprot enabled as low event may or may not happen
depending on the actual test configuration.

Modify the test_memcontrol.c to ignore low event in the 3rd child cgroup
with memory_recursiveprot on.

The 4th child cgroup has no memory usage and so has an effective
low of 0. It has no low event count because the mem_cgroup_below_low()
check in shrink_node_memcgs() is skipped as mem_cgroup_below_min()
returns true. If we ever change mem_cgroup_below_min() in such a way
that it no longer skips the no usage case, we will have to add code to
explicitly skip it.

With this patch applied, the test_memcg_low sub-test finishes
successfully without failure in most cases. Though both test_memcg_low
and test_memcg_min sub-tests may still fail occasionally if the
memory.current values fall outside of the expected ranges.

Suggested-by: Michal Koutný <mkoutny@...e.com>
Signed-off-by: Waiman Long <longman@...hat.com>
---
 .../testing/selftests/cgroup/test_memcontrol.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index 16f5d74ae762..58602c1831f1 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -380,10 +380,11 @@ static bool reclaim_until(const char *memcg, long goal);
  *
  * Then it checks actual memory usages and expects that:
  * A/B    memory.current ~= 50M
- * A/B/C  memory.current ~= 29M
- * A/B/D  memory.current ~= 21M
- * A/B/E  memory.current ~= 0
- * A/B/F  memory.current  = 0
+ * A/B/C  memory.current ~= 29M [memory.events:low > 0]
+ * A/B/D  memory.current ~= 21M [memory.events:low > 0]
+ * A/B/E  memory.current ~= 0   [memory.events:low == 0 if !memory_recursiveprot,
+ *				 undefined otherwise]
+ * A/B/F  memory.current  = 0   [memory.events:low == 0]
  * (for origin of the numbers, see model in memcg_protection.m.)
  *
  * After that it tries to allocate more than there is
@@ -525,7 +526,14 @@ static int test_memcg_protection(const char *root, bool min)
 		goto cleanup;
 	}

+	/*
+	 * Child 2 has memory.low=0, but some low protection may still be
+	 * distributed down from its parent with memory.low=50M if cgroup2
+	 * memory_recursiveprot mount option is enabled. Ignore the low
+	 * event count in this case.
+	 */
 	for (i = 0; i < ARRAY_SIZE(children); i++) {
+		int ignore_low_events_index = has_recursiveprot ? 2 : -1;
 		int no_low_events_index = 1;
 		long low, oom;

@@ -534,6 +542,8 @@ static int test_memcg_protection(const char *root, bool min)

 		if (oom)
 			goto cleanup;
+		if (i == ignore_low_events_index)
+			continue;
 		if (i <= no_low_events_index && low <= 0)
 			goto cleanup;
 		if (i > no_low_events_index && low)
-- 
2.49.0