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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 C0FC9C5CFC0 for ; Sat, 16 Jun 2018 05:42:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70E1A208B5 for ; Sat, 16 Jun 2018 05:42:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70E1A208B5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753972AbeFPFk5 (ORCPT ); Sat, 16 Jun 2018 01:40:57 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:7617 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751407AbeFPFk4 (ORCPT ); Sat, 16 Jun 2018 01:40:56 -0400 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate15.nvidia.com (using TLS: TLSv1, AES128-SHA) id ; Fri, 15 Jun 2018 22:40:37 -0700 Received: from HQMAIL107.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 15 Jun 2018 22:40:55 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 15 Jun 2018 22:40:55 -0700 Received: from [10.110.48.28] (10.110.48.28) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Sat, 16 Jun 2018 05:40:55 +0000 Subject: Re: OpenAFS module libafs.ko uses GPL-only symbol '__put_devmap_managed_page' To: Dan Williams CC: Joe Gorse , Linux Kernel Mailing List , Andrew Morton , Linux MM , Christoph Hellwig References: <1970355c-ebca-7f7d-38f7-ceac1ae553fb@nvidia.com> From: John Hubbard X-Nvconfidentiality: public Message-ID: Date: Fri, 15 Jun 2018 22:40:01 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.110.48.28] X-ClientProxiedBy: HQMAIL103.nvidia.com (172.20.187.11) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/15/2018 10:22 PM, Dan Williams wrote: > On Fri, Jun 15, 2018 at 9:43 PM, John Hubbard wrote: >> On 06/13/2018 12:51 PM, Dan Williams wrote: >>> [ adding Andrew, Christoph, and linux-mm ] >>> >>> On Wed, Jun 13, 2018 at 12:33 PM, Joe Gorse wrote: [snip] >>>> >>>> P.S. The build failure, for the morbidly curious: >>>>> FATAL: modpost: GPL-incompatible module libafs.ko uses GPL-only symbol >>>>> '__put_devmap_managed_page' >>>>> scripts/Makefile.modpost:92: recipe for target '__modpost' failed >>>>> make[6]: *** [__modpost] Error 1 >>> >>> I think the right answer here is to make __put_devmap_managed_page() >>> EXPORT_SYMBOL(), since features like devm_memremap_pages() want to >>> change the behavior of all users of put_page(). It again holds that >>> devm_memremap_pages() needs to become EXPORT_SYMBOL_GPL() because it, >>> not put_page(), is the interface that is leaking control of core >>> kernel state/infrastructure to its users. >>> >> >> Hi Dan and all, >> >> It looks like put_page() also picks up one more GPL symbol: >> devmap_managed_key. >> >> put_page >> put_devmap_managed_page >> devmap_managed_key >> >> __put_devmap_managed_page >> >> >> So if the goal is to restore put_page() to be effectively EXPORT_SYMBOL >> again, then I think there would also need to be either a non-inlined >> wrapper for devmap_managed_key (awkward for a static key), or else make >> it EXPORT_SYMBOL, or maybe something else that's less obvious to me at the >> moment. > > Right, certainly flipping the key is a kernel internal detail since it > is giving the dev_pagemap owner purview over all kernel page events, > but put_page() users are silent consumers. And you're right there's > currently no good way I see to export the 'producer' and 'consumer' > side of the key with different export types. > It's hard to imagine how anyone could end up using devmap_managed_key in an out-of-tree driver, given that other related symbols are already locked down with EXPORT_SYMBOL_GPL. So one easy fix might be to just make it EXPORT_SYMBOL, with a comment that explains the intent, and just call it a day: /* This is intended to be EXPORT_SYMBOL_GPL, but actually doing so would * cause a problem for put_page(). */ EXPORT_SYMBOL(devmap_managed_key); ...I'm sort of winging it here... :)