cgroup: account for memory_localevents in test_memcg_oom_group_leaf_events()

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.

Link: https://lkml.kernel.org/r/20220423155619.3669555-4-void@manifault.com
Signed-off-by: David Vernet <void@manifault.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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;
 
 /*
@@ -1200,6 +1201,7 @@ 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");
@@ -1345,14 +1347,20 @@ static int test_memcg_oom_group_score_events(const char *root)
 	if (!cg_run(memcg, alloc_anon, (void *)MB(100)))
 		goto cleanup;
 
-	if (cg_read_key_long(memcg, "memory.events", "oom_kill ") != 3)
+	parent_oom_events = cg_read_key_long(
-		goto cleanup;
+			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;
 
 	if (kill(safe_pid, SIGKILL))
 		goto cleanup;
 
-	ret = KSFT_PASS;
-
 cleanup:
 	if (memcg)
 		cg_destroy(memcg);
@@ -1361,7 +1369,6 @@ cleanup:
 	return ret;
 }
 
-
 #define T(x) { x, #x }
 struct memcg_test {
 	int (*fn)(const char *root);
@@ -1408,6 +1415,11 @@ 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: