[PATCH v2 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>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 .../selftests/cgroup/test_memcontrol.c        | 21 +++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index d37e8dfb1248..e899b3f28c22 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");
@@ -1128,10 +1130,16 @@ 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)
-		goto cleanup;
-
-	ret = KSFT_PASS;
+	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 && parent_oom_events == 0) ||
+	    parent_oom_events > 0)
+		ret = KSFT_PASS;
 
 cleanup:
 	if (child)
@@ -1298,6 +1306,11 @@ 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