From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751058AbcFRFIy (ORCPT <rfc822;w@1wt.eu>);
	Sat, 18 Jun 2016 01:08:54 -0400
Received: from szxga02-in.huawei.com ([119.145.14.65]:63076 "EHLO
	szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750760AbcFRFIx (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 18 Jun 2016 01:08:53 -0400
Message-ID: <5764D72B.2080800@huawei.com>
Date: Sat, 18 Jun 2016 13:07:55 +0800
From: zhong jiang <zhongjiang@huawei.com>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
MIME-Version: 1.0
To: Mike Kravetz <mike.kravetz@oracle.com>
CC: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Michal Hocko <mhocko@kernel.org>, <akpm@linux-foundation.org>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: fix account pmd page to the process
References: <1466076971-24609-1-git-send-email-zhongjiang@huawei.com> <20160616154214.GA12284@dhcp22.suse.cz> <20160616154324.GN6836@dhcp22.suse.cz> <71df66ac-df29-9542-bfa9-7c94f374df5b@oracle.com> <20160616163119.GP6836@dhcp22.suse.cz> <bf76cc6c-a0da-98f9-4a89-0bb6161f5adf@oracle.com> <20160617122506.GC6534@node.shutemov.name> <8141c2df-5643-4ba9-42a5-5b536517cdee@oracle.com>
In-Reply-To: <8141c2df-5643-4ba9-42a5-5b536517cdee@oracle.com>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.177.29.68]
X-CFilter-Loop: Reflected
X-Mirapoint-Virus-RAPID-Raw: score=unknown(0),
	refid=str=0001.0A090202.5764D736.00A7,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0,
	ip=0.0.0.0,
	so=2013-06-18 04:22:30,
	dmn=2013-03-21 17:37:32
X-Mirapoint-Loop-Id: 8350be02768a4555f384b42b187d94de
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 2016/6/17 23:39, Mike Kravetz wrote:
> On 06/17/2016 05:25 AM, Kirill A. Shutemov wrote:
>> From fd22922e7b4664e83653a84331f0a95b985bff0c Mon Sep 17 00:00:00 2001
>> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Date: Fri, 17 Jun 2016 15:07:03 +0300
>> Subject: [PATCH] hugetlb: fix nr_pmds accounting with shared page tables
>>
>> We account HugeTLB's shared page table to all processes who share it.
>> The accounting happens during huge_pmd_share().
>>
>> If somebody populates pud entry under us, we should decrease pagetable's
>> refcount and decrease nr_pmds of the process.
>>
>> By mistake, I increase nr_pmds again in this case. :-/
>> It will lead to "BUG: non-zero nr_pmds on freeing mm: 2" on process'
>> exit.
>>
>> Let's fix this by increasing nr_pmds only when we're sure that the page
>> table will be used.
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Nice,
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
>
> I agree that we do not necessarily need a back port.  I have not seen
> reports of people experiencing this race and seeing the BUG (on mm
> tear-down).
>
> zhongjiang, did someone actually hit the BUG?  Or, did you find it by
> code examination?
>
  just code examination.