selftests/bpf: add test case for BPF-THP inheritance across fork

Verify that child processes correctly inherit BPF-THP policy from their
parent during fork() operations.

Signed-off-by: Yafang Shao <[email protected]>

Author: laoar

tools/testing/selftests/bpf/prog_tests/thp_adjust.c

@@ -267,6 +267,37 @@ static void subtest_thp_global_policy(void)
 	bpf_link__destroy(global_link);
 }
 
+static void subtest_thp_fork(void)
+{
+	int elighble, child, pid, status;
+	struct bpf_link *ops_link;
+	char *ptr;
+
+	ops_link = bpf_map__attach_struct_ops(skel->maps.thp_eligible_ops);
+	if (!ASSERT_OK_PTR(ops_link, "attach struct_ops"))
+		return;
+
+	child = fork();
+	if (!ASSERT_GE(child, 0, "fork"))
+		goto destroy;
+
+	if (child == 0) {
+		ptr = thp_alloc();
+		elighble = get_thp_eligible(getpid(), (unsigned long)ptr);
+		ASSERT_EQ(elighble, 0, "THPeligible");
+		thp_free(ptr);
+
+		exit(EXIT_SUCCESS);
+	}
+
+	pid = waitpid(child, &status, 0);
+	ASSERT_EQ(pid, child, "waitpid");
+
+destroy:
+	bpf_link__destroy(ops_link);
+
+}
+
 static int thp_adjust_setup(void)
 {
 	int err = -1, pmd_order;
@@ -319,6 +350,8 @@ void test_thp_adjust(void)
 		subtest_thp_policy_update();
 	if (test__start_subtest("global_policy"))
 		subtest_thp_global_policy();
+	if (test__start_subtest("thp_fork"))
+		subtest_thp_fork();
 
 	thp_adjust_destroy();
 }