[PATCH 3/5] cgroup: Account for memory_localevents in test_memcg_oom_group_leaf_events()

[David Vernet <void@manifault.com>]

The test_memcg_oom_group_leaf_events() testcase in the cgroup memcg tests
validates that processes in a group that perform allocations exceeding
memory.oom.group are killed. It also validates that the
memory.events.oom_kill events are properly propagated in this case.  Commit
06e11c907ea4 ("kselftests: memcg: update the oom group leaf events test")
fixed test_memcg_oom_group_leaf_events() to account for the fact that the
memory.events.oom_kill events in a child cgroup is propagated up to its
parent. This behavior can actually be configured by the memory_localevents
mount option, so this patch updates the testcase to properly account for
the possible presence of this mount option.

Signed-off-by: David Vernet <void@manifault.com>
---
 .../testing/selftests/cgroup/test_memcontrol.c  | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index ea2fd27e52df..d88e0ca3f3d1 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -21,6 +21,7 @@
 #include "../kselftest.h"
 #include "cgroup_util.h"
 
+static bool has_localevents;
 static bool has_recursiveprot;
 
 /*
@@ -1091,6 +1092,7 @@ static int test_memcg_oom_group_leaf_events(const char *root)
 {
 	int ret = KSFT_FAIL;
 	char *parent, *child;
+	long parent_oom_events;
 
 	parent = cg_name(root, "memcg_test_0");
 	child = cg_name(root, "memcg_test_0/memcg_test_1");
@@ -1128,7 +1130,15 @@ static int test_memcg_oom_group_leaf_events(const char *root)
 	if (cg_read_key_long(child, "memory.events", "oom_kill ") <= 0)
 		goto cleanup;
 
-	if (cg_read_key_long(parent, "memory.events", "oom_kill ") <= 0)
+	parent_oom_events = cg_read_key_long(
+			parent, "memory.events", "oom_kill ");
+	// If memory_localevents is not enabled (the default), the parent should
+	// count OOM events in its children groups. Otherwise, it should not
+	// have observed any events.
+	if (has_localevents) {
+		if (parent_oom_events != 0)
+			goto cleanup;
+	} else if (parent_oom_events <= 0)
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -1298,6 +1308,11 @@ int main(int argc, char **argv)
 		ksft_exit_skip("Failed to query cgroup mount option\n");
 	has_recursiveprot = proc_status;
 
+	proc_status = proc_mount_contains("memory_localevents");
+	if (proc_status < 0)
+		ksft_exit_skip("Failed to query cgroup mount option\n");
+	has_localevents = proc_status;
+
 	for (i = 0; i < ARRAY_SIZE(tests); i++) {
 		switch (tests[i].fn(root)) {
 		case KSFT_PASS:
-- 
2.30.2