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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common
 path
Date: Thu, 10 Nov 2016 09:21:34 +0000
Message-ID: <20161110092134.GD9173@hori1.linux.bs1.fc.nec.co.jp>
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To: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: "linux-mm@kvack.org" <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" <linux-kernel@vger.kernel.org>, 'Naoya Horiguchi' <nao.horiguchi@gmail.com>, 'Anshuman Khandual' <khandual@linux.vnet.ibm.com>

Hi Hillf,

On Thu, Nov 10, 2016 at 05:08:07PM +0800, Hillf Danton wrote:
> On Tuesday, November 08, 2016 7:32 AM Naoya Horiguchi wrote:
> >=20
> > @@ -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;
> >=20
> > +	if (unlikely(!pmd_present(orig_pmd)))
> > +		goto out_unlock;
> > +
>=20
> 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.

Thanks,
Naoya Horiguchi=

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