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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E1A86C433E0 for ; Tue, 23 Jun 2020 18:13:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCCE4207FB for ; Tue, 23 Jun 2020 18:13:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="XtqJqEuJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733178AbgFWSNw (ORCPT ); Tue, 23 Jun 2020 14:13:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728916AbgFWSNv (ORCPT ); Tue, 23 Jun 2020 14:13:51 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3498FC061573; Tue, 23 Jun 2020 11:13:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Esyq+AEdoh1XonloiuoRagpt95xyDAj6PU4H+a2A370=; b=XtqJqEuJ6fk19CHHDiS/uWu7m0 RAcYnkqt4nYjb3KNc+oUduIZ4BmQP6z7+ubMqv/JvBbC0/xybPxcpQOpQ/lg78gd2x3ZCJn9O6mkt Jd5I2z7aiGrouE6zK9gfUYo9bIvJl5dPbeWIYGWpiwKHEq2yefSrMbieDo8PwFR4ey3HjXZsEOZo+ kpeu2fan50uIPlXjGdc5H6SPIPfo5+/vVs7+Y3TBJ/eY4XYLK7YLqWy42vBSITC110wTLB/gjxvnQ cqjN7VtvtR9/alVFGB6linsRbGqpzYe0uAFkxKU8EndRnmKY04OLN74stY8WRWXUSKeBa9tcMtxn0 Pl+jThxQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jnnPO-0006JO-In; Tue, 23 Jun 2020 18:12:34 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 9BF5E303DA0; Tue, 23 Jun 2020 20:12:32 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8DE8F20267E51; Tue, 23 Jun 2020 20:12:32 +0200 (CEST) Date: Tue, 23 Jun 2020 20:12:32 +0200 From: Peter Zijlstra To: Marco Elver Cc: "Ahmed S. Darwish" , mingo@kernel.org, will@kernel.org, tglx@linutronix.de, x86@kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, bigeasy@linutronix.de, davem@davemloft.net, sparclinux@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, heiko.carstens@de.ibm.com, linux-s390@vger.kernel.org, linux@armlinux.org.uk Subject: Re: [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables Message-ID: <20200623181232.GB4800@hirez.programming.kicks-ass.net> References: <20200623083645.277342609@infradead.org> <20200623083721.512673481@infradead.org> <20200623150031.GA2986783@debian-buster-darwi.lab.linutronix.de> <20200623152450.GM4817@hirez.programming.kicks-ass.net> <20200623161320.GA2996373@debian-buster-darwi.lab.linutronix.de> <20200623163730.GA4800@hirez.programming.kicks-ass.net> <20200623175957.GA106514@elver.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623175957.GA106514@elver.google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 23, 2020 at 07:59:57PM +0200, Marco Elver wrote: > On Tue, Jun 23, 2020 at 06:37PM +0200, Peter Zijlstra wrote: > > On Tue, Jun 23, 2020 at 06:13:21PM +0200, Ahmed S. Darwish wrote: > > > Well, freshly merged code is using it. For example, KCSAN: > > > > > > => f1bc96210c6a ("kcsan: Make KCSAN compatible with lockdep") > > > => kernel/kcsan/report.c: > > > > > > void kcsan_report(...) > > > { > > > ... > > > /* > > > * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if > > > * we do not turn off lockdep here; this could happen due to recursion > > > * into lockdep via KCSAN if we detect a race in utilities used by > > > * lockdep. > > > */ > > > lockdep_off(); > > > ... > > > } > > > > Marco, do you remember what exactly happened there? Because I'm about to > > wreck that. That is, I'm going to make TRACE_IRQFLAGS ignore > > lockdep_off(). > > Yeah, I was trying to squash any kind of recursion: > > lockdep -> other libs -> > -> KCSAN > -> print report > -> dump stack, printk and friends > -> lockdep -> other libs > -> KCSAN ... > > Some history: > > * Initial patch to fix: > https://lore.kernel.org/lkml/20200115162512.70807-1-elver@google.com/ That patch is weird; just :=n on lockdep.c should've cured that, the rest is massive overkill. > * KCSAN+lockdep+ftrace: > https://lore.kernel.org/lkml/20200214211035.209972-1-elver@google.com/ That doesn't really have anything useful.. > lockdep now has KCSAN_SANITIZE := n, but we still need to ensure that > there are no paths out of lockdep, or the IRQ flags tracing code, that > might lead through other libs, through KCSAN, libs used to generate a > report, and back to lockdep. > > I never quite figured out the exact trace that led to corruption, but > avoiding any kind of potential for recursion was the only thing that > would avoid the check_flags() warnings. Fair enough; I'll rip it all up and boot a KCSAN kernel, see what if anything happens.