From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id F014B8E0001 for ; Tue, 22 Jan 2019 11:27:53 -0500 (EST) Received: by mail-pl1-f199.google.com with SMTP id o23so15751825pll.0 for ; Tue, 22 Jan 2019 08:27:53 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id m8si16169344pls.400.2019.01.22.08.27.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Jan 2019 08:27:52 -0800 (PST) Date: Tue, 22 Jan 2019 17:27:49 +0100 From: Greg Kroah-Hartman Subject: Re: [PATCH] mm: no need to check return value of debugfs_create functions Message-ID: <20190122162749.GA22841@kroah.com> References: <20190122152151.16139-14-gregkh@linuxfoundation.org> <20190122153102.GJ4087@dhcp22.suse.cz> <20190122155255.GA20142@kroah.com> <20190122160701.GK4087@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190122160701.GK4087@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , David Rientjes , Laura Abbott , linux-mm@kvack.org On Tue, Jan 22, 2019 at 05:07:01PM +0100, Michal Hocko wrote: > On Tue 22-01-19 16:52:55, Greg KH wrote: > > On Tue, Jan 22, 2019 at 04:31:02PM +0100, Michal Hocko wrote: > > > On Tue 22-01-19 16:21:13, Greg KH wrote: > > > [...] > > > > diff --git a/mm/memblock.c b/mm/memblock.c > > > > index 022d4cbb3618..18ee657fb918 100644 > > > > --- a/mm/memblock.c > > > > +++ b/mm/memblock.c > > > > @@ -1998,8 +1998,7 @@ DEFINE_SHOW_ATTRIBUTE(memblock_debug); > > > > static int __init memblock_init_debugfs(void) > > > > { > > > > struct dentry *root = debugfs_create_dir("memblock", NULL); > > > > - if (!root) > > > > - return -ENXIO; > > > > + > > > > debugfs_create_file("memory", 0444, root, > > > > &memblock.memory, &memblock_debug_fops); > > > > debugfs_create_file("reserved", 0444, root, > > > > > > I haven't really read the whole patch but this has just hit my eyes. Is > > > this a correct behavior? > > > > > > Documentations says: > > > * @parent: a pointer to the parent dentry for this file. This should be a > > > * directory dentry if set. If this parameter is NULL, then the > > > * file will be created in the root of the debugfs filesystem. > > > > > > so in case of failure we would get those debugfs files outside of their > > > intended scope. I believe it is much more correct to simply not create > > > anything, no? > > > > If debugfs_create_dir() returns NULL, then something is really wrong > > (you passed it an invalid pointer as the parent dentry, or free memory > > is gone), so there's nothing you can do except keep moving forward and > > take that result and pass it as any parent pointer you want to. Your > > code logic should never care if a debugfs file is created or not, it is > > "fire and forget". > > OK, but does it make any sense to continue creating files when you know > that the parent directory has failed to create? What kind of advantage > does this have? It has no advantage or disadvantage. And again, it can't really happen unless the system is out of memory and in that case, everything else just crashed anyway. > > And any result of a debugfs call, like this one, that is to be passed > > into another debugfs call, will work just fine if the first one failed > > (the second one usually will also fail, which is fine.) > > > > Also, and this is the biggest problem, everyone gets the return value > > check wrong thinking NULL will be an error, it is one type of error, but > > other ones are also returned and no one checks them properly. So just > > don't check at all, that is the design goal here. > > sounds like a poor design goal to me but not mine code to maintain so... The design goal was to make it as simple as possible to use, and that includes "you do not care about the return value". Now we do have to return a value because some people need that for when they want to make a subdirectory, or remove the file later on, otherwise I would have just had everything be a void return function :) thanks, greg k-h