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Date:   Thu, 14 Sep 2023 17:34:18 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <avkrasnov@salutedevices.com>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [PATCH net-next v8 0/4] vsock/virtio/vhost: MSG_ZEROCOPY
 preparations
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On Thu, Sep 14, 2023 at 05:05:17PM +0300, Arseniy Krasnov wrote:
>Hello Stefano,
>
>On 14.09.2023 17:07, Stefano Garzarella wrote:
>> Hi Arseniy,
>>
>> On Mon, Sep 11, 2023 at 11:22:30PM +0300, Arseniy Krasnov wrote:
>>> Hello,
>>>
>>> this patchset is first of three parts of another big patchset for
>>> MSG_ZEROCOPY flag support:
>>> https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@sberdevices.ru/
>>>
>>> During review of this series, Stefano Garzarella <sgarzare@redhat.com>
>>> suggested to split it for three parts to simplify review and merging:
>>>
>>> 1) virtio and vhost updates (for fragged skbs) <--- this patchset
>>> 2) AF_VSOCK updates (allows to enable MSG_ZEROCOPY mode and read
>>> ? tx completions) and update for Documentation/.
>>> 3) Updates for tests and utils.
>>>
>>> This series enables handling of fragged skbs in virtio and vhost parts.
>>> Newly logic won't be triggered, because SO_ZEROCOPY options is still
>>> impossible to enable at this moment (next bunch of patches from big
>>> set above will enable it).
>>>
>>> I've included changelog to some patches anyway, because there were some
>>> comments during review of last big patchset from the link above.
>>
>> Thanks, I left some comments on patch 4, the others LGTM.
>> Sorry to not having spotted them before, but moving
>> virtio_transport_alloc_skb() around the file, made the patch a little
>> confusing and difficult to review.
>
>Sure, no problem, I'll fix them! Thanks for review.
>
>>
>> In addition, I started having failures of test 14 (server: host,
>> client: guest), so I looked better to see if there was anything wrong,
>> but it fails me even without this series applied.
>>
>> It happens to me intermittently (~30%), does it happen to you?
>> Can you take a look at it?
>
>Yes! sometime ago I also started to get fails of this test, not ~30%,
>significantly rare, but it depends on environment I guess, anyway I'm going to
>look at this on the next few days

Maybe it's just a timing issue in the test, indeed we are expecting 8
bytes but we received only 3 plus the 2 bytes we received before it
seems exactly the same bytes we send with the first
`send(fd, HELLO_STR, strlen(HELLO_STR), 0);`

Since it is a stream socket, it could happen, so we should retry
the recv() or just use MSG_WAITALL.

Applying the following patch fixed the issue for me (15 mins without
errors for now):

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index 90718c2fd4ea..7b0fed9fc58d 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1129,7 +1129,7 @@ static void test_stream_virtio_skb_merge_server(const struct test_opts *opts)
         control_expectln("SEND0");

         /* Read skbuff partially. */
-       res = recv(fd, buf, 2, 0);
+       res = recv(fd, buf, 2, MSG_WAITALL);
         if (res != 2) {
                 fprintf(stderr, "expected recv(2) returns 2 bytes, got %zi\n", res);
                 exit(EXIT_FAILURE);
@@ -1138,7 +1138,7 @@ static void test_stream_virtio_skb_merge_server(const struct test_opts *opts)
         control_writeln("REPLY0");
         control_expectln("SEND1");

-       res = recv(fd, buf + 2, sizeof(buf) - 2, 0);
+       res = recv(fd, buf + 2, 8, MSG_WAITALL);
         if (res != 8) {
                 fprintf(stderr, "expected recv(2) returns 8 bytes, got %zi\n", res);
                 exit(EXIT_FAILURE);

I will check better all the cases and send a patch upstream.

Anyway it looks just an issue in our test suite :-)

Stefano

>
>Thanks, Arseniy
>
>>
>> host$ ./vsock_test --mode=server --control-port=12345 --peer-cid=4
>> ...
>> 14 - SOCK_STREAM virtio skb merge...expected recv(2) returns 8 bytes, got 3
>>
>> guest$ ./vsock_test --mode=client --control-host=192.168.133.2 --control-port=12345 --peer-cid=2
>>
>> Thanks,
>> Stefano
>>
>