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=-13.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 9651EC433DF for ; Fri, 9 Oct 2020 16:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F9082227F for ; Fri, 9 Oct 2020 16:11:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602259873; bh=PMuAxNhk0IlV+HpLBxx1Gu7eGebDilISmrDCshwbfVg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=J+FZ8I1uv6z3dgD2ELSfud1/BE77XPCVs8JCVzWsJkIdBJl9xiEWCgR4aPaMjJT1z nJsb1OCexNaFH/RMur1AlC0Z8TCr2kUjC2rbihp4uH5KZ6WwjOC5grsf+ZU8ffm1O/ ZbqOPDX5nsHY3fOIlf+MU5bRzlIMxrhRKp5QaPIA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389144AbgJIQLM (ORCPT ); Fri, 9 Oct 2020 12:11:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:54168 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389451AbgJIQLM (ORCPT ); Fri, 9 Oct 2020 12:11:12 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (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 DD8CA2225D; Fri, 9 Oct 2020 16:11:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602259871; bh=PMuAxNhk0IlV+HpLBxx1Gu7eGebDilISmrDCshwbfVg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=I971vGypKo0oDlS4tk2IjPRyAVS9CFUuQrmlyNfFkYmYCD2OdK7tTEzKNzRI9DSfu iHSfOKjDDYav/BGqR1L+N40cYi8kic0yygcZ0S6sJdWjs+gefePDDDc2/huvtE4SFb dm9UXR2JQgmc5REIQmeF3LLjWmtxWa3NX0clHotc= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 9123B35227D5; Fri, 9 Oct 2020 09:11:11 -0700 (PDT) Date: Fri, 9 Oct 2020 09:11:11 -0700 From: "Paul E. McKenney" To: Qian Cai Cc: "Peter Zijlstra (Intel)" , Steven Rostedt , Ingo Molnar , x86 , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Linux Next Mailing List , Stephen Rothwell , Boqun Feng Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion Message-ID: <20201009161111.GH29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <160223032121.7002.1269740091547117869.tip-bot2@tip-bot2> <20201009135837.GD29330@paulmck-ThinkPad-P72> <07fffca72fdd585a96ab8c45761c1ea223dc24f2.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <07fffca72fdd585a96ab8c45761c1ea223dc24f2.camel@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org On Fri, Oct 09, 2020 at 11:30:38AM -0400, Qian Cai wrote: > On Fri, 2020-10-09 at 06:58 -0700, Paul E. McKenney wrote: > > On Fri, Oct 09, 2020 at 09:41:24AM -0400, Qian Cai wrote: > > > On Fri, 2020-10-09 at 07:58 +0000, tip-bot2 for Peter Zijlstra wrote: > > > > The following commit has been merged into the locking/core branch of tip: > > > > > > > > Commit-ID: 4d004099a668c41522242aa146a38cc4eb59cb1e > > > > Gitweb: > > > > https://git.kernel.org/tip/4d004099a668c41522242aa146a38cc4eb59cb1e > > > > Author: Peter Zijlstra > > > > AuthorDate: Fri, 02 Oct 2020 11:04:21 +02:00 > > > > Committer: Ingo Molnar > > > > CommitterDate: Fri, 09 Oct 2020 08:53:30 +02:00 > > > > > > > > lockdep: Fix lockdep recursion > > > > > > > > Steve reported that lockdep_assert*irq*(), when nested inside lockdep > > > > itself, will trigger a false-positive. > > > > > > > > One example is the stack-trace code, as called from inside lockdep, > > > > triggering tracing, which in turn calls RCU, which then uses > > > > lockdep_assert_irqs_disabled(). > > > > > > > > Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per- > > > > cpu > > > > variables") > > > > Reported-by: Steven Rostedt > > > > Signed-off-by: Peter Zijlstra (Intel) > > > > Signed-off-by: Ingo Molnar > > > > > > Reverting this linux-next commit fixed booting RCU-list warnings everywhere. > > > > Is it possible that the RCU-list warnings were being wrongly suppressed > > without a21ee6055c30? As in are you certain that these RCU-list warnings > > are in fact false positives? > > I guess you mean this commit a046a86082cc ("lockdep: Fix lockdep recursion") > instead of a21ee6055c30. It is unclear to me how that commit a046a86082cc would > suddenly start to generate those warnings, although I can see it starts to use > percpu variables even though the CPU is not yet set online. > > DECLARE_PER_CPU(unsigned int, lockdep_recursion); > > Anyway, the problem is that when we in the early boot: > > start_secondary() > smp_init_secondary() > init_cpu_timer() > clockevents_register_device() > > We are taking a lock there but the CPU is not yet online, and the > __lock_acquire() would call things like hlist_for_each_entry_rcu() from > lookup_chain_cache() or register_lock_class(). Thus, triggering the RCU-list > from an offline CPU warnings. > > I am not entirely sure how to fix those though. One approach is to move the call to rcu_cpu_starting() earlier in the start_secondary() processing. It is OK to invoke rcu_cpu_starting() multiple times, so for experiemental purposes you should be able to add a new call to it just before that lock is acquired. Thanx, Paul