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 DA11AC433E0 for ; Thu, 28 May 2020 20:48:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ABBF02088E for ; Thu, 28 May 2020 20:48:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590698929; bh=4fnkVfztzwaZ5WRZ7qB4s8yjom+u7iqPNg1Zcum8IY0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=JjPhl+da6NTxDaWetqoFl80IyXrF7IoR+3YObyNQSQMtwUP3EbSi5XSgXYs1SPLRw r0a97k/4ZZI3/IgQMEKqZwc8KvZlONlFgETDyJpk5i2/IgslpG0LhJApxVPMJ1taTd R7nJNZh67X984/2m6x5Tb6Zw22ggJ0KMEHQsAQAs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407389AbgE1Uss (ORCPT ); Thu, 28 May 2020 16:48:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:54420 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407348AbgE1Usk (ORCPT ); Thu, 28 May 2020 16:48:40 -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 D46AB2074B; Thu, 28 May 2020 20:48:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590698919; bh=4fnkVfztzwaZ5WRZ7qB4s8yjom+u7iqPNg1Zcum8IY0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Gwx7O4M7zP12amtu+Uzm7jflbCnb5ioiOaPF9cmR6l4femba0+os+4LSLoYFQ4VU3 oYwLZw7rT2aXmRGPlW8Qa59da0ixArfuJp3EmGYwGnCHkJwrkbj1Sz07AP0DZXWTeA GRf7/3c4k+Hpk/30TeVKtKkPKr3MiXNNL9I8rhnA= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id BC5F635229BA; Thu, 28 May 2020 13:48:39 -0700 (PDT) Date: Thu, 28 May 2020 13:48:39 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: syzbot , Paolo Bonzini , bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org, luto@kernel.org, mingo@kernel.org, syzkaller-bugs@googlegroups.com, x86@kernel.org Subject: Re: WARNING: suspicious RCU usage in idtentry_exit Message-ID: <20200528204839.GR2869@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878shbols9.fsf@nanos.tec.linutronix.de> 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 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. > > 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