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 A2AB2C282C0 for ; Wed, 23 Jan 2019 11:55:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E56121019 for ; Wed, 23 Jan 2019 11:55:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548244540; bh=QcJD0ly2gRkoCFnAmdg9PIx3OJLhjFd3dG+J6dN/ReY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=xxpxT/vLz2qGCXDXyufk2cduAWBw4gyPVBBPW5/lcyxqsJTyMqJY7pSSIC4A7a8bg MWIhvYqRtuzky5isZ0WNc9cRrNg0jKS29VVtyT5rc9GQ4Lri+u1t/Ufpazxvx7B9Bq hRZ3YVs/GlyUhQ8DawXLU41Fh7F/FozYucrGaTpk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726364AbfAWLzi (ORCPT ); Wed, 23 Jan 2019 06:55:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:39144 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726026AbfAWLzi (ORCPT ); Wed, 23 Jan 2019 06:55:38 -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 0590321019; Wed, 23 Jan 2019 11:55:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548244537; bh=QcJD0ly2gRkoCFnAmdg9PIx3OJLhjFd3dG+J6dN/ReY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ArIfGxsIZgHPRtG1HJGWyheU4q5nym/bX84vO/q6cBRx1gg+bGOgoTBN8TVOBxs5p C+u8M0e+ZNX6m74fyOwe5XHss1ALMDtPDBctGlhfHnJSiuP/TDHL0C4knwMGgC7hyv s5z0O+O34s/iGQQPp96HeUvQTUc8UR1I6gf0KboA= Date: Wed, 23 Jan 2019 12:55:35 +0100 From: Greg Kroah-Hartman To: Michal Hocko Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , Ulf Hansson , Gary R Hook , Heiko Carstens Subject: Re: [PATCH 2/2] debugfs: return error values, not NULL Message-ID: <20190123115535.GA31237@kroah.com> References: <20190123102702.GA17123@kroah.com> <20190123102814.GB17123@kroah.com> <20190123110628.GV4087@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190123110628.GV4087@dhcp22.suse.cz> 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 Wed, Jan 23, 2019 at 12:06:28PM +0100, Michal Hocko wrote: > On Wed 23-01-19 11:28:14, Greg KH wrote: > > When an error happens, debugfs should return an error pointer value, not > > NULL. This will prevent the totally theoretical error where a debugfs > > call fails due to lack of memory, returning NULL, and that dentry value > > is then passed to another debugfs call, which would end up succeeding, > > creating a file at the root of the debugfs tree, but would then be > > impossible to remove (because you can not remove the directory NULL). > > > > So, to make everyone happy, always return errors, this makes the users > > of debugfs much simpler (they do not have to ever check the return > > value), and everyone can rest easy. > > How come this is safe at all? Say you are creating a directory by > debugfs_create_dir and then feed the return value to debugfs_create_files > as a parent. In case of error you are giving it an invalid pointer and > likely blow up unless I miss something. debugfs_create_files checks for invalid parents and will just refuse to create the file. It's always done that. > I do agree that reporting errors is better than a simple catch all NULL > but this should have been done when introduced rather than now when most > callers simply check for NULL as a failure. I'm fixing up all the "NULL is a failure" callsites in the kernel, see lkml for the first round of those patches. thanks, greg k-h