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,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9F001C07E9B for ; Wed, 7 Jul 2021 15:31:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E0B261CD5 for ; Wed, 7 Jul 2021 15:31:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232298AbhGGPdv (ORCPT ); Wed, 7 Jul 2021 11:33:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:42968 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232288AbhGGPdu (ORCPT ); Wed, 7 Jul 2021 11:33:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DC09561CBE; Wed, 7 Jul 2021 15:31:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1625671869; bh=FHvqrT07eXAHKMOJRtl9t2v4q2jbVubqFMhBm8EIjJg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MR0yDNpPbquIEQRg98cu1mJvMD+3kYTsrGc6BSkAw13hhJDQUQdD6RI7sg7TxANRN vV/ETPfoi+kvM/fhFlL5Us9nEbgB4DPCNcZLVzr+6XGYxS8t7gf+EPCZbP4j9GtSnr GgvPuJdRi+PmYruuNm32rwRgJGoVINgbzERayF7w= Date: Wed, 7 Jul 2021 17:31:06 +0200 From: Greg KH To: "J. Bruce Fields" 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: 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: <20210707151936.GB9911@fieldses.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :)