Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933379AbdCaRFe (ORCPT ); Fri, 31 Mar 2017 13:05:34 -0400 Received: from mail-vk0-f43.google.com ([209.85.213.43]:33861 "EHLO mail-vk0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933217AbdCaRFc (ORCPT ); Fri, 31 Mar 2017 13:05:32 -0400 MIME-Version: 1.0 In-Reply-To: <20170331080046.GI27098@dhcp22.suse.cz> References: <1490767322-9914-1-git-send-email-maninder1.s@samsung.com> <20170329074522.GB27994@dhcp22.suse.cz> <20170329092332epcms5p10ae8263c6e3ef14eac40e08a09eff9e6@epcms5p1> <20170329104355.GG27994@dhcp22.suse.cz> <20170331080046.GI27098@dhcp22.suse.cz> From: Joel Fernandes Date: Fri, 31 Mar 2017 10:05:29 -0700 Message-ID: Subject: Re: [PATCH v2] module: check if memory leak by module. To: Michal Hocko Cc: Vaneet Narang , Miroslav Benes , Maninder Singh , "jeyu@redhat.com" , "rusty@rustcorp.com.au" , "akpm@linux-foundation.org" , "chris@chris-wilson.co.uk" , "aryabinin@virtuozzo.com" , "joonas.lahtinen@linux.intel.com" , "keescook@chromium.org" , "pavel@ucw.cz" , "jinb.park7@gmail.com" , "anisse@astier.eu" , "rafael.j.wysocki@intel.com" , "zijun_hu@htc.com" , "mingo@kernel.org" , "mawilcox@microsoft.com" , "thgarnie@google.com" , "kirill.shutemov@linux.intel.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , PANKAJ MISHRA , Ajeet Kumar Yadav , =?UTF-8?B?7J207ZWZ67SJ?= , AMIT SAHRAWAT , =?UTF-8?B?656E66a/?= , CPGS Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2439 Lines: 54 On Fri, Mar 31, 2017 at 1:00 AM, Michal Hocko wrote: > On Thu 30-03-17 23:49:52, Joel Fernandes wrote: >> Hi Michal, >> >> On Wed, Mar 29, 2017 at 3:43 AM, Michal Hocko wrote: >> > On Wed 29-03-17 09:23:32, Vaneet Narang wrote: >> >> Hi, >> >> >> >> >> Hmm, how can you track _all_ vmalloc allocations done on behalf of the >> >> >> module? It is quite some time since I've checked kernel/module.c but >> >> >> from my vague understading your check is basically only about statically >> >> >> vmalloced areas by module loader. Is that correct? If yes then is this >> >> >> actually useful? Were there any bugs in the loader code recently? What >> >> >> led you to prepare this patch? All this should be part of the changelog! >> >> >> >> First of all there is no issue in kernel/module.c. This patch add functionality >> >> to detect scenario where some kernel module does some memory allocation but gets >> >> unloaded without doing vfree. For example >> >> static int kernel_init(void) >> >> { >> >> char * ptr = vmalloc(400 * 1024); >> >> return 0; >> >> } >> > >> > How can you track that allocation back to the module? Does this patch >> > actually works at all? Also why would be vmalloc more important than >> > kmalloc allocations? >> >> Doesn't the patch use caller's (in this case, the module is the >> caller) text address for tracking this? vma->vm->caller should track >> the caller doing the allocation? > > Not really. First of all it will be vmalloc() to be tracked in the above > the example because vmalloc is not inlined. And secondly even if the vmalloc is not inlined, but __built_in_address(0) will return the *return address* of vmalloc: >From https://gcc.gnu.org/onlinedocs/gcc-4.6.0/gcc/Return-Address.html : "The level argument is number of frames to scan up the call stack. A value of 0 yields the return address of the current function" > caller of the vmalloc was tracked then it would be hopelessly > insufficient because you would get coverage of the _direct_ module usage > of vmalloc rather than anything that the module triggered and that is > outside of the module. Which means any library function etc... Yes true, but I think the check is for direct allocations, done by the module, not indirect ones... it may not be a catch-all issues type of deal but is still IMO a good check since we already have va->vm->caller available. Thanks, Joel