Re: [PATCH bpf-next] selftests/bpf: make tcp_rtt test more robust to failures

From: Stanislav Fomichev <sdf@fomichev.me>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Stanislav Fomichev <sdf@google.com>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: make tcp_rtt test more robust to failures
Date: Wed, 11 Mar 2020 15:14:24 -0700	[thread overview]
Message-ID: <20200311221424.GB2125642@mini-arch.hsd1.ca.comcast.net> (raw)
In-Reply-To: <CAEf4BzZpL83aAhDWTyNoXtJp5W8S4Q_=+2_0UNeY=eb14hS8aQ@mail.gmail.com>

On 03/11, Andrii Nakryiko wrote:
> On Wed, Mar 11, 2020 at 1:41 PM Stanislav Fomichev <sdf@fomichev.me> wrote:
> >
> > On 03/11, Andrii Nakryiko wrote:
> > [..]
> > > +     pthread_join(tid, &server_res);
> > > +     CHECK_FAIL(IS_ERR(server_res));
> >
> > I wonder if we add (move) close(server_fd) before pthread_join(), can we
> > fix this issue without using non-blocking socket? The accept() should
> > return as soon as server_fd is closed so it's essentially your
> > 'server_done'.
> 
> That was my first attempt. Amazingly, closing listening socket FD
> doesn't unblock accept()...
Ugh :-(

In this case, feel free to slap:
Reviewed-by: Stanislav Fomichev <sdf@google.com>

My only other (minor) suggestion was to add a small delay in the first
loop:

	while (!server_done) {
		accept()
		if (!err) {
			udelay(50) <--
			continue
		}
	}

But I suppose that shouldn't be that big of a deal..