From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
Matt Bobrowski <mattbobrowski@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
linux-trace-kernel <linux-trace-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: remove unnecessary rcu_read_lock in kprobe_multi_link_prog_run
Date: Wed, 27 Aug 2025 09:21:49 -0700 [thread overview]
Message-ID: <CAADnVQLBwjVhKFptO1_CEC9q1ugT1Cy2SiG5XgtD+kr7BTrr_A@mail.gmail.com> (raw)
In-Reply-To: <20250827123814.60217-1-dongml2@chinatelecom.cn>
On Wed, Aug 27, 2025 at 5:38 AM Menglong Dong <menglong8.dong@gmail.com> wrote:
>
> Preemption is disabled in ftrace graph, which indicate rcu_read_lock. So
> the rcu_read_lock is not needed in fprobe_entry(), and it is not needed
> in kprobe_multi_link_prog_run() neither.
kprobe_busy_begin() doing preempt_disable() is an implementation
detail that might change.
Having explicit rcu_read_lock() doesn't hurt.
It's a nop anyway in PREEMPT_NONE.
pw-bot: cr
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> ---
> kernel/trace/bpf_trace.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 606007c387c5..0e79fa84a634 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2741,12 +2741,10 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
> goto out;
> }
>
> - rcu_read_lock();
> regs = ftrace_partial_regs(fregs, bpf_kprobe_multi_pt_regs_ptr());
> old_run_ctx = bpf_set_run_ctx(&run_ctx.session_ctx.run_ctx);
> err = bpf_prog_run(link->link.prog, regs);
> bpf_reset_run_ctx(old_run_ctx);
> - rcu_read_unlock();
>
> out:
> __this_cpu_dec(bpf_prog_active);
> --
> 2.51.0
>
next prev parent reply other threads:[~2025-08-27 16:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-27 12:38 [PATCH bpf-next] bpf: remove unnecessary rcu_read_lock in kprobe_multi_link_prog_run Menglong Dong
2025-08-27 16:21 ` Alexei Starovoitov [this message]
2025-08-28 1:03 ` Menglong Dong
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