netdev - Re: [PATCH v2 bpf-next 00/14] bpf: Support calling kernel function

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Message-ID: <CAEf4BzamO1YDfiq0sGy1E+6dYDsy71Lz88B8M-6Uxj_2v9Jgwg@mail.gmail.com>
Date:   Thu, 1 Apr 2021 12:52:37 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Lorenz Bauer <lmb@...udflare.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        kernel-team <kernel-team@...com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 00/14] bpf: Support calling kernel function

On Thu, Apr 1, 2021 at 12:51 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Tue, Mar 30, 2021 at 11:44:39PM -0700, Andrii Nakryiko wrote:
> > On Mon, Mar 29, 2021 at 12:11 PM Martin KaFai Lau <kafai@...com> wrote:
> > >
> > > On Mon, Mar 29, 2021 at 05:06:26PM +0100, Lorenz Bauer wrote:
> > > > On Mon, 29 Mar 2021 at 02:25, Martin KaFai Lau <kafai@...com> wrote:
> > > > >
> > > > > > > >
> > > > > > > > # pahole --version
> > > > > > > > v1.17
> > > > > > >
> > > > > > > That is the most likely reason.
> > > > > > > In lib/Kconfig.debug
> > > > > > > we have pahole >= 1.19 requirement for BTF in modules.
> > > > > > > Though your config has CUBIC=y I suspect something odd goes on.
> > > > > > > Could you please try the latest pahole 1.20 ?
> > > > > >
> > > > > > Sure, I will give it a try tomorrow, I am not in control of the CI I ran.
> > > > > Could you also check the CONFIG_DYNAMIC_FTRACE and also try 'y' if it
> > > > > is not set?
> > > >
> > > > I hit the same problem on newer pahole:
> > > >
> > > > $ pahole --version
> > > > v1.20
> > > >
> > > > CONFIG_DYNAMIC_FTRACE=y resolves the issue.
> > > Thanks for checking.
> > >
> > > pahole only generates the btf_id for external function
> > > and ftrace-able function.  Some functions in the bpf_tcp_ca_kfunc_ids list
> > > are static (e.g. cubictcp_init), so it fails during resolve_btfids.
> > >
> > > I will post a patch to limit the bpf_tcp_ca_kfunc_ids list
> > > to CONFIG_DYNAMIC_FTRACE.  I will address the pahole
> > > generation in a followup and then remove this
> > > CONFIG_DYNAMIC_FTRACE limitation.
> >
> > We should still probably add CONFIG_DYNAMIC_FTRACE=y to selftests/bpf/config?
> I thought the tracing tests have been requiring this already.  Together with

Yeah, I didn't mean that your feature suddenly requires that, it was
always a requirement before, but we always forget to add it to config
and then some users are periodically tripped up by this.

> the new kfunc call, it may be good to make it explicit in selftests/bpf/config.
> I can post a diff.