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_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 064E9C433E0 for ; Thu, 14 May 2020 14:03:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0B23205CB for ; Thu, 14 May 2020 14:03:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lca.pw header.i=@lca.pw header.b="gYeH/Ebn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726245AbgENODZ (ORCPT ); Thu, 14 May 2020 10:03:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59528 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726037AbgENODY (ORCPT ); Thu, 14 May 2020 10:03:24 -0400 Received: from mail-qk1-x741.google.com (mail-qk1-x741.google.com [IPv6:2607:f8b0:4864:20::741]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DADEC061A0C for ; Thu, 14 May 2020 07:03:24 -0700 (PDT) Received: by mail-qk1-x741.google.com with SMTP id 190so3069919qki.1 for ; Thu, 14 May 2020 07:03:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lca.pw; s=google; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=DPPma3BWcIsf3J/I70N8Nn3h+M8824Udo5W6dirat1Q=; b=gYeH/EbnoXl71eid3pRmazK7xy05PoyQl4HRdQVxqc3vUTmfBZVm9mX8lKWNLWkS9W 0g3moK8CoN2hVva4yEIlApR1lxdLjtLTKKwduXuSnphKSuR1+nZP58OquuLTWh7djnNq opJ+ui5SlJPvbZPokEDbddfDUxGwaPThaNyeWfGSxOxpCIa1EEatvy082rKKhmVJAGM1 FNLOxXGfj9+Hiu8SAoQvjk58tPQisRePOCGIqtimdEnhlLV1HO6GSy7houWypJKmcYK+ YDa/SmNui5MHlfB5K80qDpWGHNntYbYLMjhBFThcth4RwTTXXtqUjsOokOTtc73nsa+/ LpyA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=DPPma3BWcIsf3J/I70N8Nn3h+M8824Udo5W6dirat1Q=; b=oU04hEOqOkSI/tg0p1OGaOsoq41Inkp7woQk1ipYwG81R4mOl/UPGzz3cHXR2gJj7C P87tA6/GhJdYMrXei7ih752Pa5k4tEBjrGt7C3TVkwfPcMU1+rYOVT4Qifyy4OYFPI5y zjwkW5iWz2EJSZqbpGMikOfarXLLdUCs8JIWoD+xmG3kh7F2lG2qEHKkJ+CmxeABvIoa owSbupqHOlSXcOf9jJJZ/U3QS1y2+WJBjrK/5Gx10QwtmoHxgoOZampGccYURflbi10F UqiOQ/GVs1VKmsUoAofka/7R5Zuhjsw6d5onQYikpvFxknQSjzXGhU3cN7QlVCRN50Ca Oxug== X-Gm-Message-State: AOAM531awBuWaqJ19CSu4nLsnu6OO0HWLOwpmWbQ2wGumGzdMrY+jTsf vGh4FctgwIv/a026x/a+R+ZgLg== X-Google-Smtp-Source: ABdhPJyXJtAqYOZRYhFZ7uYjxNZfKgwQhSgvkhQokfCdKf9HbVI5MRMO3cZ7ualj7v4u6dbRGv3N7w== X-Received: by 2002:a37:658a:: with SMTP id z132mr4906470qkb.267.1589465002907; Thu, 14 May 2020 07:03:22 -0700 (PDT) Received: from [192.168.1.153] (pool-71-184-117-43.bstnma.fios.verizon.net. [71.184.117.43]) by smtp.gmail.com with ESMTPSA id k138sm2650919qke.55.2020.05.14.07.03.22 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 May 2020 07:03:22 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: Default enable RCU list lockdep debugging with PROVE_RCU From: Qian Cai In-Reply-To: <20200514135402.GI2869@paulmck-ThinkPad-P72> Date: Thu, 14 May 2020 10:03:21 -0400 Cc: Stephen Rothwell , Linux Next Mailing List , Linux Kernel Mailing List , Madhuparna Bhowmik , Amol Grover , Dmitry Vyukov Content-Transfer-Encoding: quoted-printable Message-Id: References: <20200514222535.259cb69e@canb.auug.org.au> <20200514133328.GG2869@paulmck-ThinkPad-P72> <20200514135402.GI2869@paulmck-ThinkPad-P72> To: "Paul E. McKenney" X-Mailer: Apple Mail (2.3608.80.23.2.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On May 14, 2020, at 9:54 AM, Paul E. McKenney = wrote: >=20 > On Thu, May 14, 2020 at 09:44:28AM -0400, Qian Cai wrote: >>=20 >>=20 >>> On May 14, 2020, at 9:33 AM, Paul E. McKenney = wrote: >>>=20 >>> On Thu, May 14, 2020 at 08:31:13AM -0400, Qian Cai wrote: >>>>=20 >>>>=20 >>>>> On May 14, 2020, at 8:25 AM, Stephen Rothwell = wrote: >>>>>=20 >>>>> Hi Paul, >>>>>=20 >>>>> This patch in the rcu tree >>>>>=20 >>>>> d13fee049fa8 ("Default enable RCU list lockdep debugging with = PROVE_RCU") >>>>>=20 >>>>> 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. :-( >>>>>=20 >>>>> Can we find another way to find all the bugs that are being = discovered >>>>> (very slowly)? >>>>=20 >>>> Alternatively, could syzbot to use PROVE_RCU=3Dn temporarily = because it can=E2=80=99t keep up with it? I personally found = PROVE_RCU_LIST=3Dy is still useful for my linux-next testing, and = don=E2=80=99t want to lose that coverage overnight. >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> Would that work for you? >>=20 >> Alternatively, how about having >>=20 >> PROVE_RCU_LIST=3Dn if DEBUG_AID_FOR_SYZBOT >>=20 >> since it is only syzbot can=E2=80=99t keep up with it? >=20 > 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. >=20 > 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. >=20 > There are a lot of ways to appraoch this. >=20 > So what would work best for everyone? If PROVE_RCU_LIST=3Dn 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. Otherwise, =E2=80=9Cselect PROVE_RCU_LIST=E2=80=9D *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.=