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[23.128.96.18]) by mx.google.com with ESMTP id ef7si2074313ejb.146.2020.11.20.09.41.03; Fri, 20 Nov 2020 09:41:27 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=UIJVTAM6; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728416AbgKTRiZ (ORCPT + 99 others); Fri, 20 Nov 2020 12:38:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:33492 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726556AbgKTRiY (ORCPT ); Fri, 20 Nov 2020 12:38:24 -0500 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 5CC512222F; Fri, 20 Nov 2020 17:38:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605893904; bh=/CM845kMFoyDAhbn2zmPsuwA5Dcqa08uUerunV9DE34=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=UIJVTAM6h7gIYyon1gTF02NLMS/beUQLxtdV4/eqdp03Ees1TuSy6FLqH3f004zSl MeCbz/+7DfVmav5zKXr/WfKpSrh8AfASFAoh64xOptvO/07904C6Xl5Rk/j0iWeN04 3Ie9mTwD7HtXG8Tx8Nj5XgdFdpd/AaF32doTwFCk= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 1B2603522637; Fri, 20 Nov 2020 09:38:24 -0800 (PST) Date: Fri, 20 Nov 2020 09:38:24 -0800 From: "Paul E. McKenney" To: Mark Rutland Cc: Marco Elver , Steven Rostedt , Anders Roxell , Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Linux Kernel Mailing List , Linux-MM , kasan-dev , rcu@vger.kernel.org, Peter Zijlstra , Tejun Heo , Lai Jiangshan , linux-arm-kernel@lists.infradead.org Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...) Message-ID: <20201120173824.GJ1437@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201118233841.GS1437@paulmck-ThinkPad-P72> <20201119125357.GA2084963@elver.google.com> <20201119151409.GU1437@paulmck-ThinkPad-P72> <20201119170259.GA2134472@elver.google.com> <20201119184854.GY1437@paulmck-ThinkPad-P72> <20201119193819.GA2601289@elver.google.com> <20201119213512.GB1437@paulmck-ThinkPad-P72> <20201120141928.GB3120165@elver.google.com> <20201120143928.GH1437@paulmck-ThinkPad-P72> <20201120152200.GD2328@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120152200.GD2328@C02TD0UTHF1T.local> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 20, 2020 at 03:22:00PM +0000, Mark Rutland wrote: > On Fri, Nov 20, 2020 at 06:39:28AM -0800, Paul E. McKenney wrote: > > On Fri, Nov 20, 2020 at 03:19:28PM +0100, Marco Elver wrote: > > > I found that disabling ftrace for some of kernel/rcu (see below) solved > > > the stalls (and any mention of deadlocks as a side-effect I assume), > > > resulting in successful boot. > > > > > > Does that provide any additional clues? I tried to narrow it down to 1-2 > > > files, but that doesn't seem to work. > > > > There were similar issues during the x86/entry work. Are the ARM guys > > doing arm64/entry work now? > > I'm currently looking at it. I had been trying to shift things to C for > a while, and right now I'm trying to fix the lockdep state tracking, > which is requiring untangling lockdep/rcu/tracing. > > The main issue I see remaining atm is that we don't save/restore the > lockdep state over exceptions taken from kernel to kernel. That could > result in lockdep thinking IRQs are disabled when they're actually > enabled (because code in the nested context might do a save/restore > while IRQs are disabled, then return to a context where IRQs are > enabled), but AFAICT shouldn't result in the inverse in most cases since > the non-NMI handlers all call lockdep_hardirqs_disabled(). > > I'm at a loss to explaim the rcu vs ftrace bits, so if you have any > pointers to the issuies ween with the x86 rework that'd be quite handy. There were several over a number of months. I especially recall issues with the direct-from-idle execution of smp_call_function*() handlers, and also with some of the special cases in the entry code, for example, reentering the kernel from the kernel. This latter could cause RCU to not be watching when it should have been or vice versa. I would of course be most aware of the issues that impinged on RCU and that were located by rcutorture. This is actually not hard to run, especially if the ARM bits in the scripting have managed to avoid bitrot. The "modprobe rcutorture" approach has fewer dependencies. Either way: https://paulmck.livejournal.com/57769.html and later posts. Thanx, Paul > Thanks, > Mark. > > > > > Thanx, Paul > > > > > Thanks, > > > -- Marco > > > > > > ------ >8 ------ > > > > > > diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile > > > index 0cfb009a99b9..678b4b094f94 100644 > > > --- a/kernel/rcu/Makefile > > > +++ b/kernel/rcu/Makefile > > > @@ -3,6 +3,13 @@ > > > # and is generally not a function of system call inputs. > > > KCOV_INSTRUMENT := n > > > > > > +ifdef CONFIG_FUNCTION_TRACER > > > +CFLAGS_REMOVE_update.o = $(CC_FLAGS_FTRACE) > > > +CFLAGS_REMOVE_sync.o = $(CC_FLAGS_FTRACE) > > > +CFLAGS_REMOVE_srcutree.o = $(CC_FLAGS_FTRACE) > > > +CFLAGS_REMOVE_tree.o = $(CC_FLAGS_FTRACE) > > > +endif > > > + > > > ifeq ($(CONFIG_KCSAN),y) > > > KBUILD_CFLAGS += -g -fno-omit-frame-pointer > > > endif