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=-3.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 AF7A4C282C3 for ; Tue, 22 Jan 2019 18:33:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B4C9217D6 for ; Tue, 22 Jan 2019 18:33:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548182033; bh=EAUgKB5MRBG268AYyy5GwVUX7cbp6D6CEq4cK/4bDos=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qsHRxu/o3wYHofyuGJGmfdzQrscRvAtgmgjTIe9hl02wTOgdHsVtQP+gTAyhQwtqe QEL2Bevnan5/W+h1OBvVvJ09PCQe/7HItU7GxEHq9wKvUKT6xEpHu984CP3ie8EZUk cn40FYkUVl5hFpHmWBjstl1HRDzVNqadXBLDFBtw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726899AbfAVSdv (ORCPT ); Tue, 22 Jan 2019 13:33:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:55570 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726120AbfAVSdv (ORCPT ); Tue, 22 Jan 2019 13:33:51 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (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 83C3D21726; Tue, 22 Jan 2019 18:33:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548182031; bh=EAUgKB5MRBG268AYyy5GwVUX7cbp6D6CEq4cK/4bDos=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DSi/QNpdgLa480rW0MPapR2CjpSbUm4sOGMYehry0sDvp9p1QOIp8M0/+dhHnE7mF OHDJBUwshgul7TVYJ25D4ADXbvu47z4IFODj6PL6VFzqvJO26K16InnVn1+CqpzhON 7uLaVkrCYiFH5ZhXIlAnxG0HCF5dSN2wVEqYzQXE= Date: Tue, 22 Jan 2019 19:33:48 +0100 From: Greg Kroah-Hartman To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, Andrew Morton , Anders Roxell , Arnd Bergmann , Michal Hocko , linux-mm@kvack.org Subject: Re: [PATCH] backing-dev: no need to check return value of debugfs_create functions Message-ID: <20190122183348.GA31271@kroah.com> References: <20190122152151.16139-8-gregkh@linuxfoundation.org> <20190122160759.mx3h7gjc23zmrvxc@linutronix.de> <20190122162503.GB22548@kroah.com> <20190122171908.c7geuvluezkjp3s7@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190122171908.c7geuvluezkjp3s7@linutronix.de> User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 22, 2019 at 06:19:08PM +0100, Sebastian Andrzej Siewior wrote: > On 2019-01-22 17:25:03 [+0100], Greg Kroah-Hartman wrote: > > > > } > > > > > > > > static void bdi_debug_unregister(struct backing_dev_info *bdi) > > > > { > > > > - debugfs_remove(bdi->debug_stats); > > > > - debugfs_remove(bdi->debug_dir); > > > > + debugfs_remove_recursive(bdi->debug_dir); > > > > > > this won't remove it. > > > > Which is fine, you don't care. > > but if you cat the stats file then it will dereference the bdi struct > which has been free(), right? Maybe, I don't know, your code is long gone, it doesn't matter :) > > But step back, how could that original call be NULL? That only happens > > if you pass it a bad parent dentry (which you didn't), or the system is > > totally out of memory (in which case you don't care as everything else > > is on fire). > > debugfs_get_inode() could do -ENOMEM and then the directory creation > fails with NULL. And if that happens, your system has worse problems :) > > > > If you return for "debug_dir == NULL" then it is a nice cleanup. > > > > No, that's not a valid thing to check for, you should not care as it > > will not happen. And if it does happen, it's ok, it's only debugfs, no > > one can rely on it, it is only for debugging. > > It might happen with ENOMEM as of now. It could happen for other reasons > in future if the code changes. As it's been that way for over a decade, I think we will be fine :) If it changes in the future, in some way that actually matters, I'll go back and fix up all of the callers. thanks, greg k-h