From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f43.google.com (mail-pb0-f43.google.com [209.85.160.43]) by kanga.kvack.org (Postfix) with ESMTP id 3BCB66B0035 for ; Fri, 14 Mar 2014 00:36:53 -0400 (EDT) Received: by mail-pb0-f43.google.com with SMTP id um1so2078207pbc.30 for ; Thu, 13 Mar 2014 21:36:52 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id nc6si4283033pbc.173.2014.03.13.21.36.51 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 13 Mar 2014 21:36:52 -0700 (PDT) Message-ID: <5322875D.1040702@oracle.com> Date: Fri, 14 Mar 2014 00:36:45 -0400 From: Sasha Levin MIME-Version: 1.0 Subject: Re: [PATCH] A long explanation for a short patch References: <1394764246-19936-1-git-send-email-jhubbard@nvidia.com> In-Reply-To: <1394764246-19936-1-git-send-email-jhubbard@nvidia.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: john.hubbard@gmail.com Cc: "Kirill A. Shutemov" , linux-mm@kvack.org, John Hubbard On 03/13/2014 10:30 PM, john.hubbard@gmail.com wrote: > From: John Hubbard > > Hi Sasha and linux-mm, > > Prior to commit 309381feaee564281c3d9e90fbca8963bb7428ad, it was > possible to build MIT-licensed (non-GPL) drivers on Fedora. Fedora is > semi-unique, in that it sets CONFIG_VM_DEBUG. > > Because Fedora sets CONFIG_VM_DEBUG, they end up pulling in > dump_page(), via VM_BUG_ON_PAGE, via get_page(). As one of the > authors of NVIDIA's new, open source, "UVM-Lite" kernel module, I > originally choose to use the kernel's get_page() routine from within > nvidia_uvm_page_cache.c, because get_page() has always seemed to be > very clearly intended for use by non-GPL, driver code. > > So I'm hoping that making get_page() widely accessible again will not > be too controversial. We did check with Fedora first, and they > responded (https://bugzilla.redhat.com/show_bug.cgi?id=1074710#c3) > that we should try to get upstream changed, before asking Fedora > to change. Their reasoning seems beneficial to Linux: leaving > CONFIG_DEBUG_VM set allows Fedora to help catch mm bugs. Thanks for pointing it out. I've definitely overlooked it as a consequence of the patch. My reasoning behind making it _GPL() was simply that it's a new export, so it's GPL unless there's a really good excuse to make it non-GPL. However, dump_page() as well as the regular VM_BUG_ON() are debug functions that access functionality which isn't essential for non-GPL modules. This isn't the first and only case where enabling debug options will turn code that was previously usable under a non-GPL license into GPL specific. For example: - CONFIG_LOCKDEP* will turn locks GPL-only. - CONFIG_DYNAMIC_DEBUG will turn module loading GPL-only. - CONFIG_SUNRPC_DEBUG will turn the net RPC code GPL-only. To keep it short, my opinion is that since it doesn't break any existing code it should be kept as _GPL(), same way it was done for various other subsystems. Also, I think that enabling CONFIG_DEBUG_VM for end-users is a very risky thing to do. I agree you'll find more bugs, but you'll also hit one of the many false-positives hidden there as well. I've reported a few of those but in some cases it's hard to determine whether it's an actual false-positive or a bug somewhere else. Since the assumption is that end-users won't have CONFIG_DEBUG_VM, they don't get all the attention they deserve and end up slipping into releases: http://www.spinics.net/lists/linux-mm/msg70368.html . Actually, I can think of a few cases where having CONFIG_DEBUG_VM enabled would qualify a rather simple code to a CVE status. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org