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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_RED 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 66420C07E9E for ; Wed, 7 Jul 2021 15:47:04 +0000 (UTC) Received: from smtp1.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 224D561CC0 for ; Wed, 7 Jul 2021 15:47:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 224D561CC0 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from localhost (localhost [127.0.0.1]) by smtp1.osuosl.org (Postfix) with ESMTP id F1EBD82EF0; Wed, 7 Jul 2021 15:47:03 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp1.osuosl.org ([127.0.0.1]) by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id RODZbo1P0yac; Wed, 7 Jul 2021 15:47:03 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [IPv6:2605:bc80:3010:104::8cd3:938]) by smtp1.osuosl.org (Postfix) with ESMTPS id 1707F82F14; Wed, 7 Jul 2021 15:47:03 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id AD24AC0023; Wed, 7 Jul 2021 15:47:02 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id CEF08C000E for ; Wed, 7 Jul 2021 15:47:00 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id B124F4067B for ; Wed, 7 Jul 2021 15:47:00 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Authentication-Results: smtp4.osuosl.org (amavisd-new); dkim=pass (1024-bit key) header.d=linuxfoundation.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 6fpTGrebw2Vi for ; Wed, 7 Jul 2021 15:46:59 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp4.osuosl.org (Postfix) with ESMTPS id DFEF84063D for ; Wed, 7 Jul 2021 15:46:59 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id C02D561CBF; Wed, 7 Jul 2021 15:46:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1625672819; bh=Y7ZD3HpwgKdJAhH7VqKAYoRj+2bXkgou/pC/tB/BHBw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ASr0NS4CZg0c0eGN/Pf9i3JGSNhun6iQU8pg8YCH+KT1ls3UFQQkT+MAdCWmagDtH P1UL7+FylG/ndkN5Peyt8ec1DwrTqaSFzSyzxwo5POGR4xeMU9yTDXhmuhaqtlxh7R v827qdjfkKfAN3KCRTHcutZG2t2cVSxVo+U3sbQo= Date: Wed, 7 Jul 2021 17:46:56 +0200 From: Greg KH To: "J. Bruce Fields" Subject: Re: [PATCH v2 1/2] fcntl: fix potential deadlocks for &fown_struct.lock Message-ID: References: <20210707023548.15872-2-desmondcheongzx@gmail.com> <14633c3be87286d811263892375f2dfa9a8ed40a.camel@kernel.org> <4dda1cad6348fced5fcfcb6140186795ed07d948.camel@kernel.org> <20210707135129.GA9446@fieldses.org> <20210707151936.GB9911@fieldses.org> <20210707153417.GA10570@fieldses.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210707153417.GA10570@fieldses.org> Cc: syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com, Jeff Layton , linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, Desmond Cheong Zhi Xi , linux-kernel-mentees@lists.linuxfoundation.org X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Wed, Jul 07, 2021 at 11:34:17AM -0400, J. Bruce Fields wrote: > On Wed, Jul 07, 2021 at 05:31:06PM +0200, Greg KH wrote: > > On Wed, Jul 07, 2021 at 11:19:36AM -0400, J. Bruce Fields wrote: > > > On Wed, Jul 07, 2021 at 05:06:45PM +0200, Greg KH wrote: > > > > On Wed, Jul 07, 2021 at 09:51:29AM -0400, J. Bruce Fields wrote: > > > > > On Wed, Jul 07, 2021 at 07:40:47AM -0400, Jeff Layton wrote: > > > > > > On Wed, 2021-07-07 at 12:51 +0200, Greg KH wrote: > > > > > > > On Wed, Jul 07, 2021 at 06:44:42AM -0400, Jeff Layton wrote: > > > > > > > > On Wed, 2021-07-07 at 08:05 +0200, Greg KH wrote: > > > > > > > > > On Wed, Jul 07, 2021 at 10:35:47AM +0800, Desmond Cheong Zhi Xi wrote: > > > > > > > > > > + WARN_ON_ONCE(irqs_disabled()); > > > > > > > > > > > > > > > > > > If this triggers, you just rebooted the box :( > > > > > > > > > > > > > > > > > > Please never do this, either properly handle the problem and return an > > > > > > > > > error, or do not check for this. It is not any type of "fix" at all, > > > > > > > > > and at most, a debugging aid while you work on the root problem. > > > > > > > > > > > > > > > > > > thanks, > > > > > > > > > > > > > > > > > > greg k-h > > > > > > > > > > > > > > > > Wait, what? Why would testing for irqs being disabled and throwing a > > > > > > > > WARN_ON in that case crash the box? > > > > > > > > > > > > > > If panic-on-warn is enabled, which is a common setting for systems these > > > > > > > days. > > > > > > > > > > > > Ok, that makes some sense. > > > > > > > > > > Wait, I don't get it. > > > > > > > > > > How are we supposed to decide when to use WARN, when to use BUG, and > > > > > when to panic? Do we really want to treat them all as equivalent? And > > > > > who exactly is turning on panic-on-warn? > > > > > > > > You never use WARN or BUG, unless the system is so messed up that you > > > > can not possibly recover from the issue. > > > > > > I've heard similar advice for BUG before, but this is the first I've > > > heard it for WARN. Do we have any guidelines for how to choose between > > > WARN and BUG? > > > > Never use either :) > > I can't tell if you're kidding. I am not. > Is there some plan to remove them? Over time, yes. And any WARN that userspace can ever hit should be removed today. > There are definitely cases where I've been able to resolve a problem > more quickly because I got a backtrace from a WARN. If you want a backtrace, ask for that, recover from the error, and move on. Do not allow userspace to reboot a machine for no good reason as again, panic-on-warn is a common setting that people use now. This is what all of the syzbot work has been doing, it triggers things that cause WARN() to be hit and so we have to fix them. thanks, greg k-h _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees