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=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 5272BC433DF for ; Fri, 29 May 2020 08:51:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3344320723 for ; Fri, 29 May 2020 08:51:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726975AbgE2Ivl (ORCPT ); Fri, 29 May 2020 04:51:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726923AbgE2Ivc (ORCPT ); Fri, 29 May 2020 04:51:32 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 003B8C08C5C6 for ; Fri, 29 May 2020 01:51:31 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jeaje-0007ry-0a; Fri, 29 May 2020 10:51:26 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 3990B100C2D; Fri, 29 May 2020 10:51:25 +0200 (CEST) From: Thomas Gleixner To: Dmitry Vyukov , "Paul E. McKenney" Cc: syzbot , Paolo Bonzini , Borislav Petkov , "H. Peter Anvin" , LKML , Andy Lutomirski , Ingo Molnar , syzkaller-bugs , the arch/x86 maintainers Subject: Re: WARNING: suspicious RCU usage in idtentry_exit In-Reply-To: References: <000000000000840d4d05a6850c73@google.com> <87wo4wnpzb.fsf@nanos.tec.linutronix.de> <20200528161143.GF2869@paulmck-ThinkPad-P72> <878shbols9.fsf@nanos.tec.linutronix.de> <20200528204839.GR2869@paulmck-ThinkPad-P72> Date: Fri, 29 May 2020 10:51:25 +0200 Message-ID: <87tuzzm8du.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dmitry, Dmitry Vyukov writes: > On Thu, May 28, 2020 at 10:48 PM Paul E. McKenney wrote: >> On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote: >> OK, from the .config, another suggestion is to build the kernel >> with CONFIG_RCU_EQS_DEBUG=y. This still requires that this issue be >> reproduced, but it might catch the problem earlier. > > How much does it slow down execution? If we enable it on syzbot, it > will affect all fuzzing done by syzbot always. > It can tolerate significant slowdown and it's far from a production > kernel (it enables KASAN, KCOV, LOCKDEP and more). But I am still > asking because some debugging features are built without performance > in mind at all (like let's just drop a global lock in every > kmalloc/free, which may be too much even for a standard debug build). It's not worse than lockdep. Thanks, tglx