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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36036C46464 for ; Wed, 8 Aug 2018 02:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1F20216F6 for ; Wed, 8 Aug 2018 02:29:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1F20216F6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726745AbeHHEqU (ORCPT ); Wed, 8 Aug 2018 00:46:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:52128 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726258AbeHHEqU (ORCPT ); Wed, 8 Aug 2018 00:46:20 -0400 Received: from vmware.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2158E216E3; Wed, 8 Aug 2018 02:28:58 +0000 (UTC) Date: Tue, 7 Aug 2018 22:28:56 -0400 From: Steven Rostedt To: Joel Fernandes Cc: Joel Fernandes , LKML , "Cc: Android Kernel" , Boqun Feng , Byungchul Park , Ingo Molnar , Masami Hiramatsu , Mathieu Desnoyers , Namhyung Kim , Paul McKenney , Peter Zijlstra , Thomas Glexiner , Tom Zanussi Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage Message-ID: <20180807222856.3ede96e7@vmware.local.home> In-Reply-To: References: <20180730222423.196630-1-joel@joelfernandes.org> <20180730222423.196630-4-joel@joelfernandes.org> <20180806155058.5ee875f4@gandalf.local.home> <20180806214300.13e63523@gandalf.local.home> <20180807094954.5137972d@gandalf.local.home> <446AE5F2-39E0-46B6-8E0B-207E003DBF20@google.com> <20180807103410.4fe203cb@gandalf.local.home> <20180807110906.3a1b0ac4@gandalf.local.home> <6B9E5DC9-0859-41B4-9B72-A7D85E9EA2AD@google.com> <20180807194515.4e549c1a@gandalf.local.home> <6D0A3FD6-2190-4CC0-A3C0-7B3759E73243@google.com> <20180807204820.50b83c6d@vmware.local.home> <20180807215522.04114097@vmware.local.home> X-Mailer: Claws Mail 3.15.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 7 Aug 2018 19:13:32 -0700 Joel Fernandes wrote: > On Tue, Aug 7, 2018 at 6:55 PM, Steven Rostedt wrote: > > On Tue, 7 Aug 2018 18:17:42 -0700 > > Joel Fernandes wrote: > > > >> From 6986af946ceb04fc9ddc6d5b45fc559b6807e465 Mon Sep 17 00:00:00 2001 > >> From: "Joel Fernandes (Google)" > >> Date: Sun, 5 Aug 2018 20:17:41 -0700 > >> Subject: [PATCH] tracepoint: Run tracepoints even after CPU is offline > >> > >> Commit f37755490fe9 ("tracepoints: Do not trace when cpu is offline") > >> causes a problem for lockdep using tracepoint code. Once a CPU is > >> offline, tracepoints donot get called, however this causes a big problem > >> for lockdep probes that need to run so that IRQ annotations are marked > >> correctly. > >> > >> A race is possible where while the CPU is going offline, an interrupt > >> can come in and then a lockdep assert causes an annotation warning: > >> > >> [ 106.551354] IRQs not enabled as expected > >> [ 106.551785] WARNING: CPU: 1 PID: 0 at kernel/time/tick-sched.c:982 > >> tick_nohz_idle_enter+0x99/0xb0 > >> [ 106.552964] Modules linked in: > >> [ 106.553299] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W > >> > >> We need tracepoints to run as late as possible. This commit fixes the > >> issue by removing the cpu_online check in tracepoint code that was > >> introduced in the mentioned commit, however we now switch to using SRCU > >> for all tracepoints and special handle calling tracepoints from NMI so > >> that we don't run into issues that result from using sched-RCU when the > >> CPUs are marked to be offline. > >> > >> Fixes: c3bc8fd637a9 ("tracing: Centralize preemptirq tracepoints and > >> unify their usage") > >> Reported-by: Masami Hiramatsu > >> Signed-off-by: Joel Fernandes (Google) > > > > > > The above change log doesn't look like it matches the NMI patch. > > > > Can you resend with just the NMI changes? I already handled the cpu > > offline ones. > > Ok, sent with "cpu offline" changes dropped, here it is: > https://lore.kernel.org/patchwork/patch/972657/ > > If you could add your Reported-by to it, that would be great as well. > > > > > But I may still have concerns with this patch. > > Ok let me know what you think. > Not sure you saw this part of my reply: > @@ -171,8 +174,7 @@ extern void syscall_unregfunc(void); > } while ((++it_func_ptr)->func); \ > } \ > \ > - if (rcuidle) \ > - srcu_read_unlock_notrace(&tracepoint_srcu, idx);\ > + srcu_read_unlock_notrace(ss, idx); \ Hmm, why do we have the two different srcu handles? Thinking about this, if this can be called by the "thunk" code, then there might be an issue. I think the "thunk" code can be called before in_nmi() is set, so we don't know if we are in an NMI or not. I need to look at that code to make sure. If in_nmi() still works, then we should use the _nmi srcu handle (if that's required). But I'm not sure using SRCU for all tracepoints is needed at this moment. I'll have to look deeper into this tomorrow. But it's getting close to the merge window, and this needs to be settled quick. Another "partial revert" may be needed until this gets settled. -- Steve