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Mon, 04 Aug 2025 06:02:31 -0700 (PDT) Received: from krava ([173.38.220.40]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-615a8f25739sm6920530a12.21.2025.08.04.06.02.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Aug 2025 06:02:30 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 4 Aug 2025 15:02:27 +0200 To: Tao Chen Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, mattbobrowski@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next] bpf: Disable migrate when kprobe_multi attach to access bpf_prog_active Message-ID: References: <20250804121615.1843956-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250804121615.1843956-1-chen.dylane@linux.dev> On Mon, Aug 04, 2025 at 08:16:15PM +0800, Tao Chen wrote: > The syscall link_create not protected by bpf_disable_instrumentation, > accessing percpu data bpf_prog_active should use cpu local_lock when > kprobe_multi program attach. > > Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") > Signed-off-by: Tao Chen > --- > kernel/trace/bpf_trace.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 3ae52978cae..f6762552e8e 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2728,23 +2728,23 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > struct pt_regs *regs; > int err; > > + migrate_disable(); > if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) { this is called all the way from graph tracer, which disables preemption in function_graph_enter_regs, so I think we can safely use __this_cpu_inc_return > bpf_prog_inc_misses_counter(link->link.prog); > err = 1; > goto out; > } > > - migrate_disable(); hum, but now I'm not sure why we disable migration in here then jirka > 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(); > - migrate_enable(); > > out: > __this_cpu_dec(bpf_prog_active); > + migrate_enable(); > return err; > } > > -- > 2.48.1 >