linux-kernel - Re: kprobes and rcu_is

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Date:   Tue, 23 May 2023 10:10:41 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     Jiri Olsa <olsajiri@...il.com>, Yonghong Song <yhs@...a.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Hao Luo <haoluo@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Song Liu <song@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Yonghong Song <yhs@...com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        kafai@...com, kpsingh@...omium.org, netdev@...r.kernel.org,
        paulmck@...nel.org, songliubraving@...com,
        Ze Gao <zegao@...cent.com>
Subject: Re: kprobes and rcu_is_watching()

[ Added a subject, as I always want to delete these emails as spam! ]

On Mon, 22 May 2023 10:07:42 +0800
Ze Gao <zegao2021@...il.com> wrote:

> Oops, I missed that. Thanks for pointing that out, which I thought is
> conditional use of rcu_is_watching before.
> 
> One last point, I think we should double check on this
>      "fentry does not filter with !rcu_is_watching"
> as quoted from Yonghong and argue whether it needs
> the same check for fentry as well.
> 

Note that trace_test_and_set_recursion() (which is used by
ftrace_test_recursion_trylock()) checks for rcu_is_watching() and
returns false if it isn't (and the trylock will fail).

-- Steve