Re: [PATCH bpf-next v4 3/3] selftests/bpf: Support nonblock for send_recv_data

[Geliang Tang <geliang@kernel.org>]

mptcp-only

Hi Matt & Mat,

On Wed, 2024-04-10 at 14:34 -0700, Martin KaFai Lau wrote:
> On 4/9/24 11:13 PM, Geliang Tang wrote:
> > From: Geliang Tang <tanggeliang@kylinos.cn>
> > 
> > Some tests, such as the MPTCP bpf tests, require send_recv_data
> > helper
> > to run in nonblock mode.
> > 
> > This patch adds nonblock support for send_recv_data(). Check if it
> > is
> > currently in nonblock mode, and if so, ignore EWOULDBLOCK to
> > continue
> > sending and receiving.
> > 
> > Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> > ---
> >   tools/testing/selftests/bpf/network_helpers.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/testing/selftests/bpf/network_helpers.c
> > b/tools/testing/selftests/bpf/network_helpers.c
> > index 137cd18ef3f2..ca16ef2b648e 100644
> > --- a/tools/testing/selftests/bpf/network_helpers.c
> > +++ b/tools/testing/selftests/bpf/network_helpers.c
> > @@ -555,6 +555,7 @@ struct send_recv_arg {
> >   static void *send_recv_server(void *arg)
> >   {
> >   	struct send_recv_arg *a = (struct send_recv_arg *)arg;
> > +	int flags = fcntl(a->fd, F_GETFL);
> >   	ssize_t nr_sent = 0, bytes = 0;
> >   	char batch[1500];
> >   	int err = 0, fd;
> > @@ -578,6 +579,8 @@ static void *send_recv_server(void *arg)
> >   		if (nr_sent == -1 && errno == EINTR)
> >   			continue;
> >   		if (nr_sent == -1) {
> > +			if (flags & O_NONBLOCK && errno ==
> > EWOULDBLOCK)
> 
> I still don't see why it needs to be a non blocking IO. mptcp should
> work
> with blocking IO also, no? Does it really need non blocking IO to
> make
> mptcp test work? I would rather stay with blocking IO in selftest as
> much as
> possible for simplicity reason.

I need some help here.

This issue is reported by Matt in "CI: MPTCP BPF tests are now
validated", and my fixes ([1] and this patch) aren't accepted by
Martin. Is it normal to get EAGAINs in this case? Please give some
suggestions.

[1]
https://patchwork.kernel.org/project/mptcp/patch/311e074a3ca0465bdc5e4c2283e334bae5ccd306.1711296000.git.tanggeliang@kylinos.cn/

Thanks,
-Geliang

> 
> I am afraid the root cause of the EAGAIN thread has not been figured
> out yet:
> https://lore.kernel.org/all/b3943f9a8bf595212b00e96ba850bf32893312cc.camel@kernel.org/
> 
> Lets drop patch 3 until it is understood why mptcp needs EAGAIN or
> non-blocking IO.
> It feels like there is some flakiness and it should be understood and
> avoided.
> 
> Other than the comment in patch 2, the first two patches lgtm. Please
> respin with
> the first two patches.
> 
> > +				continue;
> >   			err = -errno;
> >   			break;
> >   		}
> > @@ -599,6 +602,7 @@ static void *send_recv_server(void *arg)
> >   
> >   int send_recv_data(int lfd, int fd, uint32_t total_bytes)
> >   {
> > +	int flags = fcntl(lfd, F_GETFL);
> >   	ssize_t nr_recv = 0, bytes = 0;
> >   	struct send_recv_arg arg = {
> >   		.fd	= lfd,
> > @@ -622,8 +626,11 @@ int send_recv_data(int lfd, int fd, uint32_t
> > total_bytes)
> >   			       MIN(total_bytes - bytes,
> > sizeof(batch)), 0);
> >   		if (nr_recv == -1 && errno == EINTR)
> >   			continue;
> > -		if (nr_recv == -1)
> > +		if (nr_recv == -1) {
> > +			if (flags & O_NONBLOCK && errno ==
> > EWOULDBLOCK)
> > +				continue;
> >   			break;
> > +		}
> >   		bytes += nr_recv;
> >   	}
> >   
> 
>