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=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 5DFACC07E95 for ; Wed, 7 Jul 2021 15:34:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 30C4461CC5 for ; Wed, 7 Jul 2021 15:34:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231685AbhGGPhA (ORCPT ); Wed, 7 Jul 2021 11:37:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231516AbhGGPg7 (ORCPT ); Wed, 7 Jul 2021 11:36:59 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4567FC061574; Wed, 7 Jul 2021 08:34:19 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id DC693581C; Wed, 7 Jul 2021 11:34:17 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org DC693581C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1625672057; bh=kx7bZBkzdc+hE7A5f/06HWJB2o1Y2o6QSxXlXY94jc8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r8Ha6aZlcfCRLla7rg1zVPZk3LnoOmb6OxikkRdo83xo6Iurx9Yukwp9zAb52cy8F YaFmNlcZu3ogJ7TMPuIUkbxT8WMgihBfWjp4Of3UkQhnQzcvXA5MJ/pkU/emd+8eGA ErRgyF9U084fibaqcqWu9fxCa4zBWX9kLd5MCBxU= Date: Wed, 7 Jul 2021 11:34:17 -0400 From: "J. Bruce Fields" To: Greg KH Cc: Jeff Layton , Desmond Cheong Zhi Xi , viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com Subject: Re: [PATCH v2 1/2] fcntl: fix potential deadlocks for &fown_struct.lock Message-ID: <20210707153417.GA10570@fieldses.org> References: <20210707023548.15872-1-desmondcheongzx@gmail.com> <20210707023548.15872-2-desmondcheongzx@gmail.com> <14633c3be87286d811263892375f2dfa9a8ed40a.camel@kernel.org> <4dda1cad6348fced5fcfcb6140186795ed07d948.camel@kernel.org> <20210707135129.GA9446@fieldses.org> <20210707151936.GB9911@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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. Is there some plan to remove them? There are definitely cases where I've been able to resolve a problem more quickly because I got a backtrace from a WARN. --b.