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=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 591F2C63798 for ; Fri, 20 Nov 2020 14:39:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AD08922253 for ; Fri, 20 Nov 2020 14:39:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="FmgQYZ4o" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AD08922253 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 1BD396B0073; Fri, 20 Nov 2020 09:39:32 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 193396B0074; Fri, 20 Nov 2020 09:39:32 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0337C6B0075; Fri, 20 Nov 2020 09:39:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0136.hostedemail.com [216.40.44.136]) by kanga.kvack.org (Postfix) with ESMTP id BAFCE6B0073 for ; Fri, 20 Nov 2020 09:39:31 -0500 (EST) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 491453634 for ; Fri, 20 Nov 2020 14:39:31 +0000 (UTC) X-FDA: 77505054942.26.fork02_1d02e2c2734c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id 1690118010D8D for ; Fri, 20 Nov 2020 14:39:31 +0000 (UTC) X-HE-Tag: fork02_1d02e2c2734c X-Filterd-Recvd-Size: 6115 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 14:39:30 +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 0E7122224C; Fri, 20 Nov 2020 14:39:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605883169; bh=TAwBwzFSTpCTleLfZQ8+ZcWFhYmGk+5E1muhTgKlVwA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=FmgQYZ4oMCALsaw6U1qaA54aFyaUqxhNoCwtOECuPWnMfsF7iTLeFxZkhPS916SF/ rMfTurzQ/uZuMTNNsd6/8Q76z8U2b9I1LeSG2BUcxAbFvD8UnUyqLLLnUkUoPh3mc2 mL/qo8R/Mg/Ov98CmrIsF1+Xuj4oSWG9ZL/tGcC8= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id AEB373522A6E; Fri, 20 Nov 2020 06:39:28 -0800 (PST) Date: Fri, 20 Nov 2020 06:39:28 -0800 From: "Paul E. McKenney" To: Marco Elver Cc: Steven Rostedt , Anders Roxell , Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Mark Rutland , 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: <20201120143928.GH1437@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201117182915.GM1437@paulmck-ThinkPad-P72> <20201118225621.GA1770130@elver.google.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120141928.GB3120165@elver.google.com> 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 03:19:28PM +0100, Marco Elver wrote: > On Thu, Nov 19, 2020 at 01:35PM -0800, Paul E. McKenney wrote: > > On Thu, Nov 19, 2020 at 08:38:19PM +0100, Marco Elver wrote: > > > On Thu, Nov 19, 2020 at 10:48AM -0800, Paul E. McKenney wrote: > > > > On Thu, Nov 19, 2020 at 06:02:59PM +0100, Marco Elver wrote: > > > > [ . . . ] > > > > > > > I can try bisection again, or reverting some commits that might be > > > > > suspicious? But we'd need some selection of suspicious commits. > > > > > > > > The report claims that one of the rcu_node ->lock fields is held > > > > with interrupts enabled, which would indeed be bad. Except that all > > > > of the stack traces that it shows have these locks held within the > > > > scheduling-clock interrupt handler. Now with the "rcu: Don't invoke > > > > try_invoke_on_locked_down_task() with irqs disabled" but without the > > > > "sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled" > > > > commit, I understand why. With both, I don't see how this happens. > > > > > > I'm at a loss, but happy to keep bisecting and trying patches. I'm also > > > considering: > > > > > > Is it the compiler? Probably not, I tried 2 versions of GCC. > > > > > > Can we trust lockdep to precisely know IRQ state? I know there's > > > been some recent work around this, but hopefully we're not > > > affected here? > > > > > > Is QEMU buggy? > > > > > > > At this point, I am reduced to adding lockdep_assert_irqs_disabled() > > > > calls at various points in that code, as shown in the patch below. > > > > > > > > At this point, I would guess that your first priority would be the > > > > initial bug rather than this following issue, but you never know, this > > > > might well help diagnose the initial bug. > > > > > > I don't mind either way. I'm worried deadlocking the whole system might > > > be worse. > > > > Here is another set of lockdep_assert_irqs_disabled() calls on the > > off-chance that they actually find something. > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit bcca5277df3f24db15e15ccc8b05ecf346d05169 > > Author: Paul E. McKenney > > Date: Thu Nov 19 13:30:33 2020 -0800 > > > > rcu: Add lockdep_assert_irqs_disabled() to raw_spin_unlock_rcu_node() macros > > None of those triggered either. > > 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? 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