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From:   Jiri Olsa <olsajiri@gmail.com>
Date:   Mon, 15 Aug 2022 11:44:32 +0200
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Jiri Olsa <olsajiri@gmail.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, bpf <bpf@vger.kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace
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On Mon, Aug 15, 2022 at 10:03:17AM +0200, Peter Zijlstra wrote:
> On Sat, Aug 13, 2022 at 03:02:52PM -0400, Steven Rostedt wrote:
> > On Fri, 12 Aug 2022 23:18:15 +0200
> > Jiri Olsa <olsajiri@gmail.com> wrote:
> > 
> > > the patch below moves the bpf function into sepatate object and switches
> > > off the -mrecord-mcount for it.. so the function gets profile call
> > > generated but it's not visible to ftrace
> 
> Why ?!?

there's bpf dispatcher code that updates bpf_dispatcher_xdp_func
function with bpf_arch_text_poke and that can race with ftrace update
if the function is traced

the idea to solve it is to 'mark' the function independent of ftrace,
and add a way to make the function invissible to ftrace but with the
profile code fentry call generated

jirka