From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH] mm: mmu_notifier: re-fix freed page still mapped in secondary MMU Date: Thu, 18 Apr 2013 02:52:31 +0800 Message-ID: <516EEF6F.8060905@linux.vnet.ibm.com> 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> <516EECDB.6090400@linux.vnet.ibm.com> <20130417184523.GN3672@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Andrew Morton , Marcelo Tosatti , Gleb Natapov , Avi Kivity , Andrea Arcangeli , LKML , KVM , Linux Memory Management List To: Robin Holt Return-path: In-Reply-To: <20130417184523.GN3672@sgi.com> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org 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? -- 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