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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 3BA9AC43441 for ; Wed, 14 Nov 2018 23:00:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E54022419 for ; Wed, 14 Nov 2018 23:00:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E54022419 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org 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 S1728244AbeKOJGL (ORCPT ); Thu, 15 Nov 2018 04:06:11 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:47352 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbeKOJGL (ORCPT ); Thu, 15 Nov 2018 04:06:11 -0500 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id CB38BB6B; Wed, 14 Nov 2018 23:00:54 +0000 (UTC) Date: Wed, 14 Nov 2018 15:00:53 -0800 From: Andrew Morton To: Michal Hocko Cc: "Uladzislau Rezki (Sony)" , Kees Cook , Shuah Khan , linux-mm@kvack.org, LKML , Matthew Wilcox , Oleksiy Avramchenko , Thomas Gleixner Subject: Re: [RFC PATCH 1/1] vmalloc: add test driver to analyse vmalloc allocator Message-Id: <20181114150053.c3fe42507923322a0a10ae1c@linux-foundation.org> In-Reply-To: <20181114151737.GA23419@dhcp22.suse.cz> References: <20181113151629.14826-1-urezki@gmail.com> <20181113151629.14826-2-urezki@gmail.com> <20181113141046.f62f5bd88d4ebc663b0ac100@linux-foundation.org> <20181114151737.GA23419@dhcp22.suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 14 Nov 2018 16:17:37 +0100 Michal Hocko wrote: > On Tue 13-11-18 14:10:46, Andrew Morton wrote: > [...] > > > +static int vmalloc_test_init(void) > > > +{ > > > + __my_vmalloc_node_range = > > > + (void *) kallsyms_lookup_name("__vmalloc_node_range"); > > > + > > > + if (__my_vmalloc_node_range) > > > + do_concurrent_test(); > > > + > > > + return -EAGAIN; /* Fail will directly unload the module */ > > > +} > > > > It's unclear why this module needs access to the internal > > __vmalloc_node_range(). Please fully explain this in the changelog. > > > > Then, let's just export the thing. (I expect this module needs a > > Kconfig dependency on CONFIG_KALLSYMS, btw). A suitable way of doing > > that would be > > > > /* Exported for lib/test_vmalloc.c. Please do not use elsewhere */ > > EXPORT_SYMBOL_GPL(__vmalloc_node_range); > > There was a previous discussion that testing for internal infrastructure > is useful quite often and such a testing module needs an access to such > an internal infrastructure. Exporting those symbols via standard > EXPORT_SYMBOL_GPL is far from optimal because we can be pretty much sure > an abuse will arise sooner than later. I was proposing > EXPORT_SYMBOL_SELFTEST that would link only against testing modules. That's rather overdoing things, I think. If someone uses a dont-use-this symbol then they get to own both pieces when it breaks. We could simply do #define EXPORT_SYMBOL_SELFTEST EXPORT_SYMBOL_GPL then write a script which checks the tree for usages of the thus-tagged symbols outside tools/testing and lib/ (?) > If that is not viable for some reason then kallsyms_lookup_name is a > dirty-but-usable workaround. Well yes. It adds a dependency on CONFIG_KALLSYMS and will cause silent breakage if __vmalloc_node_range gets renamed, has its arguments changed, etc.