[PATCH v6 mm-new 07/10] selftests/bpf: add test case to update thp policy

[Yafang Shao <laoar.shao@gmail.com>]

EBUSY is returned when attempting to install a new BPF program while one is
already running, though updates to existing programs are permitted.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 .../selftests/bpf/prog_tests/thp_adjust.c     | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/thp_adjust.c b/tools/testing/selftests/bpf/prog_tests/thp_adjust.c
index bf367c6e6f52..6e65d7b0eb80 100644
--- a/tools/testing/selftests/bpf/prog_tests/thp_adjust.c
+++ b/tools/testing/selftests/bpf/prog_tests/thp_adjust.c
@@ -227,6 +227,27 @@ static void subtest_thp_fork(void)
 	bpf_link__destroy(ops_link);
 }
 
+static void subtest_thp_policy_update(void)
+{
+	struct bpf_link *old_link, *new_link;
+	int err;
+
+	old_link = bpf_map__attach_struct_ops(skel->maps.thp_fork_ops);
+	if (!ASSERT_OK_PTR(old_link, "attach_old_link"))
+		return;
+
+	new_link = bpf_map__attach_struct_ops(skel->maps.khugepaged_ops);
+	if (!ASSERT_NULL(new_link, "attach_new_link"))
+		goto destory_old;
+	ASSERT_EQ(errno, EBUSY, "attach_new_link");
+
+	err = bpf_link__update_map(old_link, skel->maps.khugepaged_ops);
+	ASSERT_EQ(err, 0, "update_old_link");
+
+destory_old:
+	bpf_link__destroy(old_link);
+}
+
 static int thp_adjust_setup(void)
 {
 	int err, cgrp_fd, cgrp_id, pmd_order;
@@ -308,6 +329,8 @@ void test_thp_adjust(void)
 		subtest_thp_policy();
 	if (test__start_subtest("khugepaged_fork"))
 		subtest_thp_fork();
+	if (test__start_subtest("policy_update"))
+		subtest_thp_policy_update();
 
 	thp_adjust_destroy();
 }
-- 
2.47.3