From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4513C77B7C for ; Sun, 21 May 2023 11:50:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230366AbjEULuY (ORCPT ); Sun, 21 May 2023 07:50:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34680 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230417AbjEUKLt (ORCPT ); Sun, 21 May 2023 06:11:49 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E2E821A1; Sun, 21 May 2023 03:09:15 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 759A960EF8; Sun, 21 May 2023 10:09:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE2D0C433D2; Sun, 21 May 2023 10:09:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684663754; bh=YiYXte2Ov4q718ZuslBI02BeUfZ/XQCo7cBMxKqJ824=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=mw9Q3VHP/cRbht7elt1Q233Yql9KvZxMyXfDt1dD+6cvrhNc5lTYS3OfVB0K8R60a Xcc+J5kO0F+PwLqOAd8PUXF2VGC4oQ7wi9loy0w87My9nrYDicgJjSSq4KX/gddgb4 WfW/JRp7Ced9irmKomN/XnWrVjC57qgQApmT5m3av1cPpWjLLpQq8JEiCrlak2imze C1hd+kD9GUgNM1bKru4dcv6f680I8r9BgSeXoZUMPt2EtD8FWs1Ks4RzsiFHni8mvK dso6QAPza3HG+m391BBBpAlHQd+PQaVqkvtWCELH+gzaDCHpZen9+bKbQOpDjl0rwb Xm+THbVEhlM2w== Date: Sun, 21 May 2023 19:09:07 +0900 From: Masami Hiramatsu (Google) To: Jiri Olsa Cc: Ze Gao , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Hao Luo , John Fastabend , KP Singh , Martin KaFai Lau , Masami Hiramatsu , Song Liu , Stanislav Fomichev , Steven Rostedt , Yonghong Song , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, kafai@fb.com, kpsingh@chromium.org, netdev@vger.kernel.org, paulmck@kernel.org, songliubraving@fb.com, Ze Gao Subject: Re: Message-Id: <20230521190907.e4104a653583dfac785e379a@kernel.org> In-Reply-To: References: <20220515203653.4039075-1-jolsa@kernel.org> <20230520094722.5393-1-zegao@tencent.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 21 May 2023 10:08:46 +0200 Jiri Olsa wrote: > On Sat, May 20, 2023 at 05:47:24PM +0800, Ze Gao wrote: > > > > Hi Jiri, > > > > Would you like to consider to add rcu_is_watching check in > > to solve this from the viewpoint of kprobe_multi_link_prog_run > > I think this was discussed in here: > https://lore.kernel.org/bpf/20230321020103.13494-1-laoar.shao@gmail.com/ > > and was considered a bug, there's fix mentioned later in the thread > > there's also this recent patchset: > https://lore.kernel.org/bpf/20230517034510.15639-3-zegao@tencent.com/ > > that solves related problems I think this rcu_is_watching() is a bit different issue. This rcu_is_watching() check is required if the kprobe_multi_link_prog_run() uses any RCU API. E.g. rethook_try_get() is also checks rcu_is_watching() because it uses call_rcu(). Thank you, > > > itself? And accounting of missed runs can be added as well > > to imporve observability. > > right, we count fprobe->nmissed but it's not exposed, we should allow > to get 'missed' stats from both fprobe and kprobe_multi later, which > is missing now, will check > > thanks, > jirka > > > > > Regards, > > Ze > > > > > > ----------------- > > From 29fd3cd713e65461325c2703cf5246a6fae5d4fe Mon Sep 17 00:00:00 2001 > > From: Ze Gao > > Date: Sat, 20 May 2023 17:32:05 +0800 > > Subject: [PATCH] bpf: kprobe_multi runs bpf progs only when rcu_is_watching > > > > From the perspective of kprobe_multi_link_prog_run, any traceable > > functions can be attached while bpf progs need specical care and > > ought to be under rcu protection. To solve the likely rcu lockdep > > warns once for good, when (future) functions in idle path were > > attached accidentally, we better paying some cost to check at least > > in kernel-side, and return when rcu is not watching, which helps > > to avoid any unpredictable results. > > > > Signed-off-by: Ze Gao > > --- > > kernel/trace/bpf_trace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 9a050e36dc6c..3e6ea7274765 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -2622,7 +2622,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > > struct bpf_run_ctx *old_run_ctx; > > int err; > > > > - if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) { > > + if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1 || !rcu_is_watching())) { > > err = 0; > > goto out; > > } > > -- > > 2.40.1 > > -- Masami Hiramatsu (Google)