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=-16.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 303A0C388F7 for ; Thu, 29 Oct 2020 01:01:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D21C9207BC for ; Thu, 29 Oct 2020 01:01:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603933300; bh=CYqqIQeLVQ2GDg8Qk4O7/yPF87bpo8HOJdgeKmVSG7M=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=w1wXD2ZmPTP/Ktw2YH2oaIc+p48PH0InMxdW6AcINimG3zJUz48pc093CAPO5FS1o 6TaBNuMfhyfpzTIKd5tlcgGbzCvi2kc9JksV6ntgfGFzIvcsAoGop1o4RndDWvER37 cXkz0+rNCT8jLV/fY8Qo1C201NSFZzX2G99jOZrU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403950AbgJ2BBk (ORCPT ); Wed, 28 Oct 2020 21:01:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:60476 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731506AbgJ1WRY (ORCPT ); Wed, 28 Oct 2020 18:17:24 -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 943282244C; Wed, 28 Oct 2020 03:01:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603854090; bh=CYqqIQeLVQ2GDg8Qk4O7/yPF87bpo8HOJdgeKmVSG7M=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=J34e3ugmDw0+RgNgHi7V7cZnahdwYN5VL3pKtKMK88THY++wGQRPmSL5RXWpre6+W dWeTJBj1I+WlGeDc66wKb3HdjZ9gD2JJuoYHopHiwAwVcrUqKcuCX5kGYHh509xQ1f fKaxChn52bKktbUlgXICpAo1sIW2WgfYZSTyDnaU= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4F3683521849; Tue, 27 Oct 2020 20:01:30 -0700 (PDT) Date: Tue, 27 Oct 2020 20:01:30 -0700 From: "Paul E. McKenney" To: Qian Cai Cc: Boqun Feng , "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 Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion Message-ID: <20201028030130.GB3249@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <160223032121.7002.1269740091547117869.tip-bot2@tip-bot2> <20201012031110.GA39540@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> <1db80eb9676124836809421e85e1aa782c269a80.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1db80eb9676124836809421e85e1aa782c269a80.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 Tue, Oct 27, 2020 at 03:31:41PM -0400, Qian Cai wrote: > On Mon, 2020-10-12 at 11:11 +0800, Boqun Feng wrote: > > Hi, > > > > 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. > > > > > > > I think this happened because in this commit debug_lockdep_rcu_enabled() > > didn't adopt to the change that made lockdep_recursion a percpu > > variable? > > > > Qian, mind to try the following? > > Boqun, Paul, may I ask what's the latest with the fixes? I must admit that I got > lost in this thread, but I remember that the patch from Boqun below at least > silence quite some of those warnings if not all. The problem is that some of > those warnings would trigger a lockdep circular locks warning due to printk() > with some locks held which in turn disabling the lockdep, makes our test runs > inefficient. If I have the right email thread associated with the right fixes, these commits in -rcu should be what you are looking for: 73b658b6b7d5 ("rcu: Prevent lockdep-RCU splats on lock acquisition/release") 626b79aa935a ("x86/smpboot: Move rcu_cpu_starting() earlier") And maybe this one as well: 3a6f638cb95b ("rcu,ftrace: Fix ftrace recursion") Please let me know if these commits do not fix things. Thanx, Paul > > Although, arguably the problem still exists, i.e. we still have an RCU > > read-side critical section inside lock_acquire(), which may be called on > > a yet-to-online CPU, which RCU doesn't watch. I think this used to be OK > > because we don't "free" anything from lockdep, IOW, there is no > > synchronize_rcu() or call_rcu() that _needs_ to wait for the RCU > > read-side critical sections inside lockdep. But now we lock class > > recycling, so it might be a problem. > > > > That said, currently validate_chain() and lock class recycling are > > mutually excluded via graph_lock, so we are safe for this one ;-) > > > > ----------->8 > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > > index 39334d2d2b37..35d9bab65b75 100644 > > --- a/kernel/rcu/update.c > > +++ b/kernel/rcu/update.c > > @@ -275,8 +275,8 @@ EXPORT_SYMBOL_GPL(rcu_callback_map); > > > > noinstr int notrace debug_lockdep_rcu_enabled(void) > > { > > - return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks && > > - current->lockdep_recursion == 0; > > + return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && > > + __lockdep_enabled; > > } > > EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); > >