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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 AFE44C63798 for ; Thu, 19 Nov 2020 22:54:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B4E720BED for ; Thu, 19 Nov 2020 22:54:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="kL3PAxbG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726648AbgKSWyA (ORCPT ); Thu, 19 Nov 2020 17:54:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:35846 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726234AbgKSWyA (ORCPT ); Thu, 19 Nov 2020 17:54:00 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 7B8022078D; Thu, 19 Nov 2020 22:53:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605826439; bh=cyOhmgdck5bcUe3yZHXRL+9ZgqweKbNI89Rawb9k2oA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kL3PAxbGhIafzcP+yn+XTRJ5cnGQQusUt3dwLbUjKVttfqpW5ZKn7G9As98kHpgEh yrkXB/xjTOmWrUUK4IlpdZ4fxY0fVLSoXqlTShkI7PEm4TELJqOrdO+OAF3PiQy0Zd lIwLSfGTlM1h+e5zNMrhujlorNkmMS7GA7cV+3ig= Date: Thu, 19 Nov 2020 22:53:53 +0000 From: Will Deacon To: "Paul E. McKenney" Cc: Marco Elver , 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: <20201119225352.GA5251@willie-the-truck> References: <20201117105236.GA1964407@elver.google.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201119213512.GB1437@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 19, 2020 at 01:35:12PM -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. FWIW, arm64 is known broken wrt lockdep and irq tracing atm. Mark has been looking at that and I think he is close to having something workable. Mark -- is there anything Marco and Paul can try out? Will