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Tue, 05 Aug 2025 09:04:34 -0700 (PDT) Received: from krava ([176.74.159.170]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-af92b650c8asm790559666b.65.2025.08.05.09.04.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Aug 2025 09:04:34 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Tue, 5 Aug 2025 18:04:32 +0200 To: Tao Chen Cc: song@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, 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: Remove migrate_disable in kprobe_multi_link_prog_run Message-ID: References: <20250805122312.1890951-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: linux-trace-kernel@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: <20250805122312.1890951-1-chen.dylane@linux.dev> On Tue, Aug 05, 2025 at 08:23:12PM +0800, Tao Chen wrote: > bpf program should run under migration disabled, kprobe_multi_link_prog_run > called the way from graph tracer, which disables preemption in > function_graph_enter_regs, as Jiri and Yonghong suggested, there is no > need to use migrate_disable. As a result, some overhead maybe will be > reduced. > > Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") > Signed-off-by: Tao Chen Acked-by: Jiri Olsa thanks, jirka > --- > kernel/trace/bpf_trace.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 3ae52978cae..1993fc62539 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2734,14 +2734,19 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > goto out; > } > > - migrate_disable(); > + /* > + * bpf program should run under migration disabled, kprobe_multi_link_prog_run > + * called the way from graph tracer, which disables preemption in nit, s/called the way/called all the way/ > + * function_graph_enter_regs, so there is no need to use migrate_disable. > + * Accessing the above percpu data bpf_prog_active is also safe for the same > + * reason. > + */ > 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); > -- > 2.48.1 >