Re: [PATCH bpf-next v2] selftests/bpf: Wait for wq callback before checking ok_sleepable

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Sun, Nov 01, 2026 at 06:36 PM Jonathan Bastari Thamrin via B4 Relay <devnull+thamrinjonathan.gmail.com@kernel.org> wrote:
>  	ASSERT_OK(err, "test_run");
>  	ASSERT_EQ(topts.retval, 0, "test_run");
>
> -	usleep(50); /* 10 usecs should be enough, but give it extra */
> -
> +	/* wait for wq callback to finish */
> +	while (!READ_ONCE(wq_skel->bss->wq_cb_run))
> +		sched_yield();

This loop can spin forever.
The two ASSERTs above it don't stop the test. When retval != 0 nothing
starts the wq and wq_cb_run stays 0.

  what goes wrong                  today   with the patch
  -------------------------------  ------  --------------
  test_run fails or retval != 0    FAIL    hang
  the callback doesn't run         FAIL    hang
  the callback gets a wrong key    FAIL    FAIL

The second row is what this test is for.
The watchdog doesn't help. watchdog_timer_func() sends one SIGSEGV.
crash_handler() prints the stack and returns. The loop goes on.

Waiting for the callback is right. Waiting forever is not.
Keep the loop bounded, like prog_tests/ksock_wq.c.
Then there is no need for wq_cb_run and for the changes in progs/wq.c.

Something like this (not even compile tested):

diff --git a/tools/testing/selftests/bpf/prog_tests/wq.c b/tools/testing/selftests/bpf/prog_tests/wq.c
index 97926e3..c4de70b 100644
--- a/tools/testing/selftests/bpf/prog_tests/wq.c
+++ b/tools/testing/selftests/bpf/prog_tests/wq.c
@@ -7,7 +7,7 @@
 void serial_test_wq(void)
 {
 	struct wq *wq_skel = NULL;
-	int err, prog_fd;
+	int err, prog_fd, i;

 	LIBBPF_OPTS(bpf_test_run_opts, topts);

@@ -25,11 +25,13 @@ void serial_test_wq(void)

 	prog_fd = bpf_program__fd(wq_skel->progs.test_syscall_array_sleepable);
 	err = bpf_prog_test_run_opts(prog_fd, &topts);
-	ASSERT_OK(err, "test_run");
-	ASSERT_EQ(topts.retval, 0, "test_run");
-
-	usleep(50); /* 10 usecs should be enough, but give it extra */
+	if (!ASSERT_OK(err, "test_run") ||
+	    !ASSERT_EQ(topts.retval, 0, "test_run"))
+		goto clean_up;

+	/* The callback runs in a kworker. Fail instead of a hang if it doesn't. */
+	for (i = 0; i < 10000 && !READ_ONCE(wq_skel->bss->ok_sleepable); i++)
+		usleep(1000);
 	ASSERT_EQ(wq_skel->bss->ok_sleepable, (1 << 1), "ok_sleepable");
 clean_up:
 	wq__destroy(wq_skel);

pw-bot: cr