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Thu, 25 Oct 2018 03:43:00 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 25 Oct 2018 12:42:57 +0200 To: Michal Hocko Cc: Uladzislau Rezki , Joel Fernandes , Shuah Khan , Matthew Wilcox , Kees Cook , Andrew Morton , linux-mm@kvack.org, LKML , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Joel Fernandes , Thomas Gleixner , Ingo Molnar , Tejun Heo , maco@android.com Subject: Re: [RFC PATCH 0/2] improve vmalloc allocation Message-ID: <20181025104257.adtktxmggxewspvy@pc636> References: <20181022165253.uphv3xzqivh44o3d@pc636> <20181023072306.GN18839@dhcp22.suse.cz> <20181023152640.GD20085@bombadil.infradead.org> <20181023170532.GW18839@dhcp22.suse.cz> <98842edb-d462-96b1-311f-27c6ebfc108a@kernel.org> <20181023193044.GA139403@joelaf.mtv.corp.google.com> <20181024062252.GA18839@dhcp22.suse.cz> <20181024173418.2bxkdjbcyzfkgfeu@pc636> <20181025084327.GN18839@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181025084327.GN18839@dhcp22.suse.cz> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 25, 2018 at 10:43:27AM +0200, Michal Hocko wrote: > On Wed 24-10-18 19:34:18, Uladzislau Rezki wrote: > > Hi. > > > > On Wed, Oct 24, 2018 at 08:22:52AM +0200, Michal Hocko wrote: > > > On Tue 23-10-18 12:30:44, Joel Fernandes wrote: > > > > On Tue, Oct 23, 2018 at 11:13:36AM -0600, Shuah Khan wrote: > > > > > On 10/23/2018 11:05 AM, Michal Hocko wrote: > > > > > > On Tue 23-10-18 08:26:40, Matthew Wilcox wrote: > > > > > >> On Tue, Oct 23, 2018 at 09:02:56AM -0600, Shuah Khan wrote: > > > > > > [...] > > > > > >>> The way it can be handled is by adding a test module under lib. test_kmod, > > > > > >>> test_sysctl, test_user_copy etc. > > > > > >> > > > > > >> The problem is that said module can only invoke functions which are > > > > > >> exported using EXPORT_SYMBOL. And there's a cost to exporting them, > > > > > >> which I don't think we're willing to pay, purely to get test coverage. > > > > > > > > > > > > Yes, I think we do not want to export internal functionality which might > > > > > > be still interesting for the testing coverage. Maybe we want something > > > > > > like EXPORT_SYMBOL_KSELFTEST which would allow to link within the > > > > > > kselftest machinery but it wouldn't allow the same for general modules > > > > > > and will not give any API promisses. > > > > > > > > > > > > > > > > I like this proposal. I think we will open up lot of test opportunities with > > > > > this approach. > > > > > > > > > > Maybe we can use this stress test as a pilot and see where it takes us. > > > > > > > > I am a bit worried that such an EXPORT_SYMBOL_KSELFTEST mechanism can be abused by > > > > out-of-tree module writers to call internal functionality. > > > > > > > > How would you prevent that? > > > > > > There is no way to prevent non-exported symbols abuse by 3rd party > > > AFAIK. EXPORT_SYMBOL_* is not there to prohibid abuse. It is a mere > > > signal of what is, well, an exported API. > > > > Can we just use kallsyms_lookup_name()? > > Heh, this is the abuse I've had in mind ;) > > > > static void *((*__my_vmalloc_node_range)(unsigned long size, > > unsigned long align,unsigned long start, unsigned long end, > > gfp_t gfp_mask,pgprot_t prot, unsigned long vm_flags, > > int node, const void *caller)); > > > > __my_vmalloc_node_range = (void *) kallsyms_lookup_name("__vmalloc_node_range"); > > > > This is just too ugly to live. So I would go with it only if there is no > reasonable way to export what tests need with a sane interface. Agree, that is a bit ugly and not generic even though it is easy :) -- Vlad Rezki