From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756753Ab3DQSlp (ORCPT ); Wed, 17 Apr 2013 14:41:45 -0400 Received: from e28smtp06.in.ibm.com ([122.248.162.6]:51557 "EHLO e28smtp06.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755495Ab3DQSlo (ORCPT ); Wed, 17 Apr 2013 14:41:44 -0400 Message-ID: <516EECDB.6090400@linux.vnet.ibm.com> Date: Thu, 18 Apr 2013 02:41:31 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Robin Holt CC: Andrew Morton , Marcelo Tosatti , Gleb Natapov , Avi Kivity , Andrea Arcangeli , LKML , KVM , Linux Memory Management List Subject: Re: [PATCH] mm: mmu_notifier: re-fix freed page still mapped in secondary MMU References: <516CF235.4060103@linux.vnet.ibm.com> <20130416093131.GJ3658@sgi.com> <516D275C.8040406@linux.vnet.ibm.com> <20130416112553.GM3658@sgi.com> <20130416114322.GN3658@sgi.com> <516D4D08.9020602@linux.vnet.ibm.com> <20130416180835.GY3658@sgi.com> <516E0F1E.5090805@linux.vnet.ibm.com> <20130417141035.GA29872@sgi.com> In-Reply-To: <20130417141035.GA29872@sgi.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13041718-9574-0000-0000-00000781253E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/17/2013 10:10 PM, Robin Holt wrote: > On Wed, Apr 17, 2013 at 10:55:26AM +0800, Xiao Guangrong wrote: >> On 04/17/2013 02:08 AM, Robin Holt wrote: >>> On Tue, Apr 16, 2013 at 09:07:20PM +0800, Xiao Guangrong wrote: >>>> On 04/16/2013 07:43 PM, Robin Holt wrote: >>>>> Argh. Taking a step back helped clear my head. >>>>> >>>>> For the -stable releases, I agree we should just go with your >>>>> revert-plus-hlist_del_init_rcu patch. I will give it a test >>>>> when I am in the office. >>>> >>>> Okay. Wait for your test report. Thank you in advance. >>>> >>>>> >>>>> For the v3.10 release, we should work on making this more >>>>> correct and completely documented. >>>> >>>> Better document is always welcomed. >>>> >>>> Double call ->release is not bad, like i mentioned it in the changelog: >>>> >>>> it is really rare (e.g, can not happen on kvm since mmu-notify is unregistered >>>> after exit_mmap()) and the later call of multiple ->release should be >>>> fast since all the pages have already been released by the first call. >>>> >>>> But, of course, it's great if you have a _light_ way to avoid this. >>> >>> Getting my test environment set back up took longer than I would have liked. >>> >>> Your patch passed. I got no NULL-pointer derefs. >> >> Thanks for your test again. >> >>> >>> How would you feel about adding the following to your patch? >> >> I prefer to make these changes as a separate patch, this change is the >> improvement, please do not mix it with bugfix. > > I think your "improvement" classification is a bit deceiving. My previous > patch fixed the bug in calling release multiple times. Your patch without > this will reintroduce that buggy behavior. Just because the bug is already > worked around by KVM does not mean it is not a bug. As your tested, calling ->release() multiple times can work, but just make your testcase more _slower_. So your changes is trying to speed it up - it is a improvement. Well, _if_ it is really a bug, could you please do not fix two bugs in one patch? Thanks!