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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E031FA3741 for ; Mon, 24 Oct 2022 14:11:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230171AbiJXOKu (ORCPT ); Mon, 24 Oct 2022 10:10:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235131AbiJXOJE (ORCPT ); Mon, 24 Oct 2022 10:09:04 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 7B5B2C4D90; Mon, 24 Oct 2022 05:51:14 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1C6D3ED1; Mon, 24 Oct 2022 05:21:07 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.7.186]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D2D8A3F7B4; Mon, 24 Oct 2022 05:20:59 -0700 (PDT) Date: Mon, 24 Oct 2022 13:20:57 +0100 From: Mark Rutland To: Yu Liao Cc: "Paul E. McKenney" , "liwei (GF)" , linux-kernel@vger.kernel.org, rcu@vger.kernel.org Subject: Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick Message-ID: References: <20221012064911.GN4221@paulmck-ThinkPad-P17-Gen-1> <97cfec0d-a24b-9917-2bd1-404e344eaa36@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <97cfec0d-a24b-9917-2bd1-404e344eaa36@huawei.com> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Oct 20, 2022 at 09:32:35PM +0800, Yu Liao wrote: > On 2022/10/19 22:14, Mark Rutland wrote: > > On Tue, Oct 18, 2022 at 03:24:48PM +0100, Mark Rutland wrote: > > Having a go with v6.1-rc1, placing a kprobe on __rcu_irq_enter_check_tick() > > causes a recursive exception which triggers the stack overflow detection, so > > there are bigger problems here, and we'll need to do some further rework of the > > arm64 entry code. FWIW, x86-64 seems fine. > > > > I have a vague recollection that that there was something (some part kprobes, > > perhaps) that didn't like being called in NMI context, which is why debug > > exceptions aren't accounted as true NMIs (but get most of the same treatment). > > > > I'll have to dig into this a bit more; there are a bunch of subtle interactions > > in this area, and I don't want to put a band-aid over this without fully > > understanding the implications. > > > > Once we've figured that out for mainline, we can figure out what needs to go to > > stable. > > > > Yu, were you particularly interested in tracing __rcu_irq_enter_check_tick(), > > or did you stumble upon this by other means? > Oh，This was found with the help of the kernel fuzzer syzkaller. Thanks for confirming! I've also been testing with Syzkaller, but it looks like I haven't had KPROBES enabled due to deselecting MODULE support, which explains how I've missed this until now. :/ I'll go fiddle with moy configs. Thanks, Mark.