selftests/bpf: Ensure sleepable program is rejected by hash map iter

Add a test to ensure sleepable program is rejected by hash map iterator.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220810080538.1845898-10-houtao@huaweicloud.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -679,6 +679,12 @@ static void test_bpf_hash_map(void)
 			goto out;
 	}
 
+	/* Sleepable program is prohibited for hash map iterator */
+	linfo.map.map_fd = map_fd;
+	link = bpf_program__attach_iter(skel->progs.sleepable_dummy_dump, &opts);
+	if (!ASSERT_ERR_PTR(link, "attach_sleepable_prog_to_iter"))
+		goto out;
+
 	linfo.map.map_fd = map_fd;
 	link = bpf_program__attach_iter(skel->progs.dump_bpf_hash_map, &opts);
 	if (!ASSERT_OK_PTR(link, "attach_iter"))

tools/testing/selftests/bpf/progs/bpf_iter_bpf_hash_map.c

@@ -112,3 +112,12 @@ int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)
 
 	return 0;
 }
+
+SEC("iter.s/bpf_map_elem")
+int sleepable_dummy_dump(struct bpf_iter__bpf_map_elem *ctx)
+{
+	if (ctx->meta->seq_num == 0)
+		BPF_SEQ_PRINTF(ctx->meta->seq, "map dump starts\n");
+
+	return 0;
+}