Re: [PATCH net-next v8 0/4] vsock/virtio/vhost: MSG_ZEROCOPY preparations

[Stefano Garzarella]

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@xxxxxxxxxxxxxx/
> > >
> > > During review of this series, Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > 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