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

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Date: Wed, 30 Aug 2023 10:10:52 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Xu Kuohai <xukuohai@...weicloud.com>, bpf@...r.kernel.org,
 netdev@...r.kernel.org, John Fastabend <john.fastabend@...il.com>,
 Bobby Eshleman <bobby.eshleman@...edance.com>
Cc: Jakub Sitnicki <jakub@...udflare.com>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
 Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH bpf v3 3/4] selftests/bpf: fix a CI failure caused by
 vsock sockmap test

Hi Xu,

On 8/4/23 9:37 AM, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@...wei.com>
> 
> 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@...wei.com>

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