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, URIBL_BLOCKED,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 C26B4C433E0 for ; Thu, 14 May 2020 15:34:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A17A20728 for ; Thu, 14 May 2020 15:34:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589470441; bh=c1I6NVD00/l8JyhbZoKN9BhNoOXboGGBJlhOK92sQnc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=hbMO0O//GjTSXDzqgMo08ky0ltnJibvnzdLGso9lEgmTsPl1yZLGbU8t8WG5iIUC4 P8yaRCVfpTQ3ly9v+1qjjyOxcqLJ/L2MlK+toDUe8ty4Y3VyV7Za4DVnUttvbD8de8 SeqtR4SON8pkegkcOiutcwOQUDEjLZN9o74K40qw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726191AbgENPeB (ORCPT ); Thu, 14 May 2020 11:34:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:48420 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726056AbgENPeB (ORCPT ); Thu, 14 May 2020 11:34:01 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [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 AC10C206A5; Thu, 14 May 2020 15:34:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589470440; bh=c1I6NVD00/l8JyhbZoKN9BhNoOXboGGBJlhOK92sQnc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=FIDjMi9Lctz3XO1na65x+KHBIKFfPyFg7a3xT6OfYJBxR7pU/Z/mASDJhENqsfxt9 QwtAF7Nkrp1SHNJxptfm53l35itQ2iB52uXu/fe6i6ctiGnVyFsbunm+ZOKEt+hPez Z2CSnLSKskbWfaXoLtrBmGo9hRVDRAO/JF0tnfXE= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 3687235229C5; Thu, 14 May 2020 08:34:00 -0700 (PDT) Date: Thu, 14 May 2020 08:34:00 -0700 From: "Paul E. McKenney" To: Qian Cai Cc: Stephen Rothwell , Linux Next Mailing List , Linux Kernel Mailing List , Madhuparna Bhowmik , Amol Grover , Dmitry Vyukov Subject: Re: Default enable RCU list lockdep debugging with PROVE_RCU Message-ID: <20200514153400.GJ2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200514222535.259cb69e@canb.auug.org.au> <20200514133328.GG2869@paulmck-ThinkPad-P72> <20200514135402.GI2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-next-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org On Thu, May 14, 2020 at 10:03:21AM -0400, Qian Cai wrote: > > > > On May 14, 2020, at 9:54 AM, Paul E. McKenney wrote: > > > > On Thu, May 14, 2020 at 09:44:28AM -0400, Qian Cai wrote: > >> > >> > >>> On May 14, 2020, at 9:33 AM, Paul E. McKenney wrote: > >>> > >>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote: > >>>> > >>>> > >>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell wrote: > >>>>> > >>>>> Hi Paul, > >>>>> > >>>>> This patch in the rcu tree > >>>>> > >>>>> d13fee049fa8 ("Default enable RCU list lockdep debugging with PROVE_RCU") > >>>>> > >>>>> is causing whack-a-mole in the syzbot testing of linux-next. Because > >>>>> they always do a debug build of linux-next, no testing is getting done. :-( > >>>>> > >>>>> Can we find another way to find all the bugs that are being discovered > >>>>> (very slowly)? > >>>> > >>>> Alternatively, could syzbot to use PROVE_RCU=n temporarily because it can’t keep up with it? I personally found PROVE_RCU_LIST=y is still useful for my linux-next testing, and don’t want to lose that coverage overnight. > >>> > >>> The problem is that PROVE_RCU is exactly PROVE_LOCKING, and asking people > >>> to test without PROVE_LOCKING is a no-go in my opinion. But of course > >>> on the other hand if there is no testing of RCU list lockdep debugging, > >>> those issues will never be found, let alone fixed. > >>> > >>> One approach would be to do as Stephen asks (either remove d13fee049fa8 > >>> or pull it out of -next) and have testers force-enable the RCU list > >>> lockdep debugging. > >>> > >>> Would that work for you? > >> > >> Alternatively, how about having > >> > >> PROVE_RCU_LIST=n if DEBUG_AID_FOR_SYZBOT > >> > >> since it is only syzbot can’t keep up with it? > > > > Sound good to me, assuming that this works for the syzkaller guys. > > Or could there be a "select PROVE_RCU_LIST" for the people who would > > like to test it. > > > > Alternatively, if we revert d13fee049fa8 from -next, I could provide > > you a script that updates your .config to set both RCU_EXPERT and > > PROVE_RCU_LIST. > > > > There are a lot of ways to appraoch this. > > > > So what would work best for everyone? > > > If PROVE_RCU_LIST=n if DEBUG_AID_FOR_SYZBOT works for syzbot guys, that would be great, so other testing agents could still report/fix those RCU-list bugs and then pave a way for syzbot to return back once all those false positives had been sorted out. On that, I must defer to the syzbot guys. > Otherwise, “select PROVE_RCU_LIST” *might* be better than buried into RCU_EXPERT where we will probably never saw those false positives been addressed since my configs does not cover a wide range of subsystems and probably not many other bots would enable RCU_EXPERT. Yet another option would be to edit your local kernel/rcu/Kconfig.debug and change the code to the following: config PROVE_RCU_LIST def_bool y help Enable RCU lockdep checking for list usages. It is default enabled with CONFIG_PROVE_RCU. Removing the RCU_EXPERT dependency would not go over at all well with some people whose opinions are difficult to ignore. ;-) Thanx, Paul