Re: [PATCH bpf v3 3/4] selftests/bpf: fix a CI failure caused by vsock sockmap test

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

Hi Xu,

On 8/4/23 9:37 AM, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@xxxxxxxxxx>
>
> BPF CI has reported the following failure:
>
> Error: #200/79 sockmap_listen/sockmap VSOCK test_vsock_redir
>    Error: #200/79 sockmap_listen/sockmap VSOCK test_vsock_redir
>    ./test_progs:vsock_unix_redir_connectible:1506: egress: write: Transport endpoint is not connected
>    vsock_unix_redir_connectible:FAIL:1506
>    ./test_progs:vsock_unix_redir_connectible:1506: ingress: write: Transport endpoint is not connected
>    vsock_unix_redir_connectible:FAIL:1506
>    ./test_progs:vsock_unix_redir_connectible:1506: egress: write: Transport endpoint is not connected
>    vsock_unix_redir_connectible:FAIL:1506
>    ./test_progs:vsock_unix_redir_connectible:1514: ingress: recv() err, errno=11
>    vsock_unix_redir_connectible:FAIL:1514
>    ./test_progs:vsock_unix_redir_connectible:1518: ingress: vsock socket map failed, a != b
>    vsock_unix_redir_connectible:FAIL:1518
>    ./test_progs:vsock_unix_redir_connectible:1525: ingress: want pass count 1, have 0
>
> It’s because the recv(... MSG_DONTWAIT) syscall in the test case is
> called before the queued work sk_psock_backlog() in the kernel finishes
> executing. So the data to be read is still queued in psock->ingress_skb
> and cannot be read by the user program. Therefore, the non-blocking
> recv() reads nothing and reports an EAGAIN error.
>
> So replace recv(... MSG_DONTWAIT) with xrecv_nonblock(), which calls
> select() to wait for data to be readable or timeout before calls recv().
>
> Fixes: d61bd8c1fd02 ("selftests/bpf: add a test case for vsock sockmap")
> Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>

This is unfortunately still flaky and showing up from time to time in BPF CI, e.g. a
very recent one can be found here:

https://github.com/kernel-patches/bpf/actions/runs/6021475685/job/16335248421

[...]
Error: #211 sockmap_listen
Error: #211/79 sockmap_listen/sockmap VSOCK test_vsock_redir
  Error: #211/79 sockmap_listen/sockmap VSOCK test_vsock_redir
  ./test_progs:vsock_unix_redir_connectible:1501: egress: write: Transport endpoint is not connected
  vsock_unix_redir_connectible:FAIL:1501
  ./test_progs:vsock_unix_redir_connectible:1501: ingress: write: Transport endpoint is not connected
  vsock_unix_redir_connectible:FAIL:1501
  ./test_progs:vsock_unix_redir_connectible:1501: egress: write: Transport endpoint is not connected
  vsock_unix_redir_connectible:FAIL:1501

Could you continue to look into it to make the test more robust?

Thanks a lot,
Daniel