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 A1CC9C63777 for ; Fri, 20 Nov 2020 18:58:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 298372078E for ; Fri, 20 Nov 2020 18:58:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="wJPsspjB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 298372078E 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 AE4146B005C; Fri, 20 Nov 2020 13:58:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A94756B005D; Fri, 20 Nov 2020 13:58:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 90DEC6B006C; Fri, 20 Nov 2020 13:58:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0187.hostedemail.com [216.40.44.187]) by kanga.kvack.org (Postfix) with ESMTP id 652316B005C for ; Fri, 20 Nov 2020 13:58:00 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0CF8D180AD801 for ; Fri, 20 Nov 2020 18:58:00 +0000 (UTC) X-FDA: 77505706320.02.cream74_63028f62734d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin02.hostedemail.com (Postfix) with ESMTP id E215E10097AA1 for ; Fri, 20 Nov 2020 18:57:59 +0000 (UTC) X-HE-Tag: cream74_63028f62734d X-Filterd-Recvd-Size: 5743 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 18:57:59 +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 4C01222464; Fri, 20 Nov 2020 18:57:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605898678; bh=XFTcuGAvqGRf8jCZ+ckM7jc3MC3vlz4De93JWXGu/Ro=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=wJPsspjBAtc2Maj5KcKF0b+v14djW14eYbsjEMFBRVZNoUZEi2q5wc0RTCHU1qYt0 jQ6XGn+h3U1TMAK7Hh1puIJu2qQCcqYlWwMKw10ke/QJPL7eFZMkuHm4oninm8u0Rt WxdDT/4XnMTOFNIZZF4Uy4osU6s31bBTiWBAv5K4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id E2B203522637; Fri, 20 Nov 2020 10:57:57 -0800 (PST) Date: Fri, 20 Nov 2020 10:57:57 -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: <20201120185757.GL1437@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <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> <20201120173824.GJ1437@paulmck-ThinkPad-P72> <20201120180206.GF2328@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120180206.GF2328@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 06:02:06PM +0000, Mark Rutland wrote: > On Fri, Nov 20, 2020 at 09:38:24AM -0800, Paul E. McKenney wrote: > > 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. > > Ah; those are precisely the cases I'm currently fixing, so if we're > lucky this is an indirect result of one of those rather than a novel > source of pain... Here is hoping! > > 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. > > That is a very good idea. I'd been relying on Syzkaller to tickle the > issue, but the torture infrastructure is a much better fit for this > problem. I hadn't realise how comprehensive the scripting was, thanks > for this! But why not both rcutorture and Syzkaller? ;-) > I'll see about giving that a go once I have the irq-from-idle cases > sorted, as those are very obviously broken if you hack > trace_hardirqs_{on,off}() to check that RCU is watching. Sounds good! Thanx, Paul