linux-kernel - Re: [PATCH bpf-next 5/6] bpf: Improve tracing recursion prevention mechanism

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Date:   Thu, 27 Apr 2023 08:39:21 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Yafang Shao <laoar.shao@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        bpf <bpf@...r.kernel.org>, linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 5/6] bpf: Improve tracing recursion prevention mechanism

On Thu, Apr 27, 2023 at 8:36 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 27 Apr 2023 23:23:31 +0800
> Yafang Shao <laoar.shao@...il.com> wrote:
>
> > > But I thought you can run a bpf_prog from another bpf_prog. So you don't
> > > want to prevent it. You need other logic to detect if it was not suppose to
> > > recurs.
> > >
> >
> > If so, we have to keep the prog->active to prevent it, then I'm not
> > sure if it is worth adding test_recursion_*().
>
> I thought that the whole point of this exercise was because the
> migrate_disable() itself could be traced (or call something that can), and
> that's outside of prog->active protection. Which the test_recursion_*()
> code was created for.

Not sure where did this come from.
migrate_enable/disable were added to deny list back in 2021.