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Reply-To: "Hillf Danton" <hillf.zj@alibaba-inc.com>
From: "Hillf Danton" <hillf.zj@alibaba-inc.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>
In-Reply-To: <1478561517-4317-8-git-send-email-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 17:08:07 +0800
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To: 'Naoya Horiguchi' <n-horiguchi@ah.jp.nec.com>, linux-mm@kvack.org
Cc: "'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>

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 ?

>  	page = pmd_page(orig_pmd);
>  	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
>  	/*
[...]
> @@ -3591,6 +3591,10 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		int ret;
> 
>  		barrier();
> +		if (unlikely(is_pmd_migration_entry(orig_pmd))) {
> +			pmd_migration_entry_wait(mm, fe.pmd);
> +			return 0;
> +		}
>  		if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
>  			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
>  				return do_huge_pmd_numa_page(&fe, orig_pmd);

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