Re: [PATCH bpf-next] selftests/bpf: Fix spurious failures in accept due to EAGAIN

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Mar 12, 2020 at 10:11 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>
> Andrii Nakryiko reports that sockmap_listen test suite is frequently
> failing due to accept() calls erroring out with EAGAIN:
>
>   ./test_progs:connect_accept_thread:733: accept: Resource temporarily unavailable
>   connect_accept_thread:FAIL:733
>
> This is because we are needlessly putting the listening TCP sockets in
> non-blocking mode.
>
> Fix it by using the default blocking mode in all tests in this suite.
>
> Fixes: 44d28be2b8d4 ("selftests/bpf: Tests for sockmap/sockhash holding listening sockets")
> Reported-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---

Thanks for looking into this. Can you please verify that test
successfully fails (not hangs) when, say, network is down (do `ip link
set lo down` before running test?). The reason I'm asking is that I
just fixed a problem in tcp_rtt selftest, in which accept() would
block forever, even if listening socket was closed.


>  tools/testing/selftests/bpf/prog_tests/sockmap_listen.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> index 52aa468bdccd..90271ec90388 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> @@ -754,7 +754,7 @@ static void test_syn_recv_insert_delete(int family, int sotype, int mapfd)
>         int err, s;
>         u64 value;
>
> -       s = socket_loopback(family, sotype | SOCK_NONBLOCK);
> +       s = socket_loopback(family, sotype);
>         if (s < 0)
>                 return;
>
> @@ -896,7 +896,7 @@ static void redir_to_connected(int family, int sotype, int sock_mapfd,
>
>         zero_verdict_count(verd_mapfd);
>
> -       s = socket_loopback(family, sotype | SOCK_NONBLOCK);
> +       s = socket_loopback(family, sotype);
>         if (s < 0)
>                 return;
>
> @@ -1028,7 +1028,7 @@ static void redir_to_listening(int family, int sotype, int sock_mapfd,
>
>         zero_verdict_count(verd_mapfd);
>
> -       s = socket_loopback(family, sotype | SOCK_NONBLOCK);
> +       s = socket_loopback(family, sotype);
>         if (s < 0)
>                 return;
>
> --
> 2.24.1
>