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=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 3D2EEC2D0E4 for ; Fri, 20 Nov 2020 17:38:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 855E62225B for ; Fri, 20 Nov 2020 17:38:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="UIJVTAM6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 855E62225B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E3FB56B0071; Fri, 20 Nov 2020 12:38:26 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DEEF46B0072; Fri, 20 Nov 2020 12:38:26 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D2BF46B0073; Fri, 20 Nov 2020 12:38:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 943266B0071 for ; Fri, 20 Nov 2020 12:38:26 -0500 (EST) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 32FF9181AC9BF for ; Fri, 20 Nov 2020 17:38:26 +0000 (UTC) X-FDA: 77505505812.18.power91_3a0b3f52734d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin18.hostedemail.com (Postfix) with ESMTP id 155BC100EDBEE for ; Fri, 20 Nov 2020 17:38:26 +0000 (UTC) X-HE-Tag: power91_3a0b3f52734d X-Filterd-Recvd-Size: 5581 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf46.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 17:38:25 +0000 (UTC) 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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