selftests/bpf_iter: Don't fail test due to missing __builtin_btf_type_id

The new test for task iteration in bpf_iter checks (in do_btf_read()) if it
should be skipped due to missing __builtin_btf_type_id. However, this
'skip' verdict is not propagated to the caller, so the parent test will
still fail. Fix this by also skipping the rest of the parent test if the
skip condition was reached.

Fixes: b72091bd4e ("selftests/bpf: Add test for bpf_seq_printf_btf helper")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20200929123004.46694-1-toke@redhat.com

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

@@ -172,17 +172,18 @@ done:
 
 static char taskbuf[TASKBUFSZ];
 
-static void do_btf_read(struct bpf_iter_task_btf *skel)
+static int do_btf_read(struct bpf_iter_task_btf *skel)
 {
 	struct bpf_program *prog = skel->progs.dump_task_struct;
 	struct bpf_iter_task_btf__bss *bss = skel->bss;
 	int iter_fd = -1, len = 0, bufleft = TASKBUFSZ;
 	struct bpf_link *link;
 	char *buf = taskbuf;
+	int ret = 0;
 
 	link = bpf_program__attach_iter(prog, NULL);
 	if (CHECK(IS_ERR(link), "attach_iter", "attach_iter failed\n"))
-		return;
+		return ret;
 
 	iter_fd = bpf_iter_create(bpf_link__fd(link));
 	if (CHECK(iter_fd < 0, "create_iter", "create_iter failed\n"))
@@ -198,6 +199,7 @@ static void do_btf_read(struct bpf_iter_task_btf *skel)
 
 	if (bss->skip) {
 		printf("%s:SKIP:no __builtin_btf_type_id\n", __func__);
+		ret = 1;
 		test__skip();
 		goto free_link;
 	}
@@ -212,12 +214,14 @@ free_link:
 	if (iter_fd > 0)
 		close(iter_fd);
 	bpf_link__destroy(link);
+	return ret;
 }
 
 static void test_task_btf(void)
 {
 	struct bpf_iter_task_btf__bss *bss;
 	struct bpf_iter_task_btf *skel;
+	int ret;
 
 	skel = bpf_iter_task_btf__open_and_load();
 	if (CHECK(!skel, "bpf_iter_task_btf__open_and_load",
@@ -226,7 +230,9 @@ static void test_task_btf(void)
 
 	bss = skel->bss;
 
-	do_btf_read(skel);
+	ret = do_btf_read(skel);
+	if (ret)
+		goto cleanup;
 
 	if (CHECK(bss->tasks == 0, "check if iterated over tasks",
 		  "no task iteration, did BPF program run?\n"))