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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>,
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        "'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>
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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
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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.