linux-kernel - Re: [PATCH net v2] vsock/test: Fix occasional failure in SIOCOUTQ tests

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Message-ID: <CAGxU2F6ssoadHjCH9qi6HdaproC3rH=d-CdYh2mvK+_X4-C4nw@mail.gmail.com>
Date: Wed, 7 May 2025 17:41:54 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Konstantin Shkolnyy <kshk@...ux.ibm.com>
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, mjrosato@...ux.ibm.com
Subject: Re: [PATCH net v2] vsock/test: Fix occasional failure in SIOCOUTQ tests

On Wed, 7 May 2025 at 17:15, Konstantin Shkolnyy <kshk@...ux.ibm.com> wrote:
>
> These tests:
>     "SOCK_STREAM ioctl(SIOCOUTQ) 0 unsent bytes"
>     "SOCK_SEQPACKET ioctl(SIOCOUTQ) 0 unsent bytes"
> output: "Unexpected 'SIOCOUTQ' value, expected 0, got 64 (CLIENT)".
>
> They test that the SIOCOUTQ ioctl reports 0 unsent bytes after the data
> have been received by the other side. However, sometimes there is a delay
> in updating this "unsent bytes" counter, and the test fails even though
> the counter properly goes to 0 several milliseconds later.
>
> The delay occurs in the kernel because the used buffer notification
> callback virtio_vsock_tx_done(), called upon receipt of the data by the
> other side, doesn't update the counter itself. It delegates that to
> a kernel thread (via vsock->tx_work). Sometimes that thread is delayed
> more than the test expects.
>
> Change the test to poll SIOCOUTQ until it returns 0 or a timeout occurs.
>
> Signed-off-by: Konstantin Shkolnyy <kshk@...ux.ibm.com>
> ---
> Changes in v2:
>  - Use timeout_check() to end polling, instead of counting iterations.

Why removing the sleep?

Thanks,
Stefano

>
>  tools/testing/vsock/vsock_test.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> index d0f6d253ac72..613551132a96 100644
> --- a/tools/testing/vsock/vsock_test.c
> +++ b/tools/testing/vsock/vsock_test.c
> @@ -1264,21 +1264,25 @@ static void test_unsent_bytes_client(const struct test_opts *opts, int type)
>         send_buf(fd, buf, sizeof(buf), 0, sizeof(buf));
>         control_expectln("RECEIVED");
>
> -       ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
> -       if (ret < 0) {
> -               if (errno == EOPNOTSUPP) {
> -                       fprintf(stderr, "Test skipped, SIOCOUTQ not supported.\n");
> -               } else {
> +       /* SIOCOUTQ isn't guaranteed to instantly track sent data. Even though
> +        * the "RECEIVED" message means that the other side has received the
> +        * data, there can be a delay in our kernel before updating the "unsent
> +        * bytes" counter. Repeat SIOCOUTQ until it returns 0.
> +        */
> +       timeout_begin(TIMEOUT);
> +       do {
> +               ret = ioctl(fd, SIOCOUTQ, &sock_bytes_unsent);
> +               if (ret < 0) {
> +                       if (errno == EOPNOTSUPP) {
> +                               fprintf(stderr, "Test skipped, SIOCOUTQ not supported.\n");
> +                               break;
> +                       }
>                         perror("ioctl");
>                         exit(EXIT_FAILURE);
>                 }
> -       } else if (ret == 0 && sock_bytes_unsent != 0) {
> -               fprintf(stderr,
> -                       "Unexpected 'SIOCOUTQ' value, expected 0, got %i\n",
> -                       sock_bytes_unsent);
> -               exit(EXIT_FAILURE);
> -       }
> -
> +               timeout_check("SIOCOUTQ");
> +       } while (sock_bytes_unsent != 0);
> +       timeout_end();
>         close(fd);
>  }
>
> --
> 2.34.1
>