From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx177.postini.com [74.125.245.177]) by kanga.kvack.org (Postfix) with SMTP id 3EEEE6B0175 for ; Wed, 1 May 2013 05:03:42 -0400 (EDT) Date: Wed, 1 May 2013 04:03:38 -0500 From: Robin Holt Subject: Re: [PATCH] mm: mmu_notifier: re-fix freed page still mapped in secondary MMU Message-ID: <20130501090338.GP3658@sgi.com> References: <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> <516EECDB.6090400@linux.vnet.ibm.com> <20130417184523.GN3672@sgi.com> <516EEF6F.8060905@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <516EEF6F.8060905@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Xiao Guangrong Cc: Robin Holt , Andrew Morton , Marcelo Tosatti , Gleb Natapov , Avi Kivity , Andrea Arcangeli , LKML , KVM , Linux Memory Management List On Thu, Apr 18, 2013 at 02:52:31AM +0800, Xiao Guangrong wrote: > On 04/18/2013 02:45 AM, Robin Holt wrote: > > >>>>>>> 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? > > > > The code, as is, does not call ->release() multiple times. Your code > > changes the behavior to call it multiple times. You are introducing the > > bug by your code changes. Why not fix the bug you create in the patch > > which creates it? > > Andrew, your thought? > What ever happened with this? Robin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org