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=-2.6 required=3.0 tests=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 73F38C433DF for ; Fri, 29 May 2020 14:05:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E9C0206E2 for ; Fri, 29 May 2020 14:05:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590761123; bh=DAEX1BrrY5wL9k9zq0w57zLiw5vneyLFzT1YguTHKHE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=ErGybIzFK4YmjBI5PXEaqy2pTVJsxghgvZ0zY4Rl2som8KGXkXv8ikp5Cg7US2jxw dl0sJuh09kQRGXD+oex7DNMhyUISLl8r5g9VyTMMseQCRfsgLVU0cIZ+1sQDqBoy2W BOKBq4JaV3vnXwjQUcJDmLa+JGj23a2q12FeSjB0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727106AbgE2OFW (ORCPT ); Fri, 29 May 2020 10:05:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:46092 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726476AbgE2OFW (ORCPT ); Fri, 29 May 2020 10:05:22 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 4A4E32073B; Fri, 29 May 2020 14:05:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590761121; bh=DAEX1BrrY5wL9k9zq0w57zLiw5vneyLFzT1YguTHKHE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=DQqEnuyUJctnk4blUl2tCMAq0iNxtQ80mdI0YhsGpg5TKfH7PYcZ9KiOJgtpvn117 68lqXlWuJjBh3742/YnAGhqU1OYnHB5sDEdbpDecQh5XyPBcFj95u7Z05fdniNp4Av 9iZdL9HgINidUjit4y5hsG3Yb8wgR2DcTWpvGsJI= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 37CA33522683; Fri, 29 May 2020 07:05:21 -0700 (PDT) Date: Fri, 29 May 2020 07:05:21 -0700 From: "Paul E. McKenney" To: Dmitry Vyukov Cc: Thomas Gleixner , 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 Message-ID: <20200529140521.GA2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 29, 2020 at 08:20:12AM +0200, Dmitry Vyukov wrote: > 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: > > > Paul, > > > > > > "Paul E. McKenney" writes: > > > > On Thu, May 28, 2020 at 03:33:44PM +0200, Thomas Gleixner wrote: > > > >> syzbot writes: > > > >> Weird. I have no idea how that thing is an EQS here. > > > > > > > > No argument on the "Weird" part! ;-) > > > > > > > > Is this a NO_HZ_FULL=y kernel? > > > > > > No, it has only NO_HZ_IDLE. > > > > > > https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10 > > > > 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 is an extra WARN_ON_ONCE() with a simple comparison, but on almost every kernel entry/exit path. So not something you want in production, but much lighter weight than any of the tools you listed above. Full disclosure: It usually fires for new architectures or for new timer hardware/drivers. Which might allow you to enable it selectively. Thanx, Paul > > > > If so, one possibility is that the call > > > > to rcu_user_exit() went missing somehow. If not, then RCU should have > > > > been watching userspace execution. > > > > > > > > Again, the only thing I can think of (should this prove to be > > > > reproducible) is the rcu_dyntick trace event. > > > > > > :) > > > > > > Thanks, > > > > > > tglx > > > > Thanx, Paul > > > > -- > > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/20200528204839.GR2869%40paulmck-ThinkPad-P72.