Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S932466AbcKJJac (ORCPT <rfc822;w@1wt.eu>);
        Thu, 10 Nov 2016 04:30:32 -0500
Received: from out0-142.mail.aliyun.com ([140.205.0.142]:57285 "EHLO
        out0-142.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753880AbcKJJaG (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 10 Nov 2016 04:30:06 -0500
X-Greylist: delayed 1220 seconds by postgrey-1.27 at vger.kernel.org; Thu, 10 Nov 2016 04:29:01 EST
X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R671e4;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03301;MF=hillf.zj@alibaba-inc.com;NM=1;PH=DS;RN=16;SR=0;TI=SMTPD_---.79aIjTm_1478770100;
Reply-To: "Hillf Danton" <hillf.zj@alibaba-inc.com>
From: "Hillf Danton" <hillf.zj@alibaba-inc.com>
To: "'Naoya Horiguchi'" <n-horiguchi@ah.jp.nec.com>
Cc: <linux-mm@kvack.org>,
        "'Kirill A. Shutemov'" <kirill.shutemov@linux.intel.com>,
        "'Hugh Dickins'" <hughd@google.com>,
        "'Andrew Morton'" <akpm@linux-foundation.org>,
        "'Dave Hansen'" <dave.hansen@intel.com>,
        "'Andrea Arcangeli'" <aarcange@redhat.com>,
        "'Mel Gorman'" <mgorman@techsingularity.net>,
        "'Michal Hocko'" <mhocko@kernel.org>,
        "'Vlastimil Babka'" <vbabka@suse.cz>,
        "'Pavel Emelyanov'" <xemul@parallels.com>,
        "'Zi Yan'" <zi.yan@cs.rutgers.edu>,
        "'Balbir Singh'" <bsingharora@gmail.com>,
        <linux-kernel@vger.kernel.org>,
        "'Naoya Horiguchi'" <nao.horiguchi@gmail.com>,
        "'Anshuman Khandual'" <khandual@linux.vnet.ibm.com>
References: <1478561517-4317-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1478561517-4317-8-git-send-email-n-horiguchi@ah.jp.nec.com> <013801d23b31$f47a7cb0$dd6f7610$@alibaba-inc.com> <20161110092134.GD9173@hori1.linux.bs1.fc.nec.co.jp>
In-Reply-To: <20161110092134.GD9173@hori1.linux.bs1.fc.nec.co.jp>
Subject: Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common path
Date: Thu, 10 Nov 2016 17:28:20 +0800
Message-ID: <014b01d23b34$c7a71600$56f54200$@alibaba-inc.com>
MIME-Version: 1.0
Content-Type: text/plain;
        charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Mailer: Microsoft Outlook 14.0
Thread-Index: AQHUTcTjuGtnqU7v9+UBKVUUSuWnDwG2qRyoAcdrSEQChlbctaCdqZpg
Content-Language: zh-cn
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 706
Lines: 18

On Thursday, November 10, 2016 5:22 PM Naoya Horiguchi wrote:
> On Thu, Nov 10, 2016 at 05:08:07PM +0800, Hillf Danton wrote:
> > On Tuesday, November 08, 2016 7:32 AM Naoya Horiguchi wrote:
> > >
> > > @@ -1013,6 +1027,9 @@ int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
> > >  	if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
> > >  		goto out_unlock;
> > >
> > > +	if (unlikely(!pmd_present(orig_pmd)))
> > > +		goto out_unlock;
> > > +
> >
> > Can we encounter a migration entry after acquiring ptl ?
> 
> I think we can. thp migration code releases ptl after converting pmd into
> migration entry, so other code can see it even within ptl.
> 
But we have a pmd_same check there, you see.