Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common path

From: "Hillf Danton" <hillf.zj@alibaba-inc.com>
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>
Subject: Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common path
Date: Thu, 10 Nov 2016 17:08:07 +0800	[thread overview]
Message-ID: <013801d23b31$f47a7cb0$dd6f7610$@alibaba-inc.com> (raw)
In-Reply-To: <1478561517-4317-8-git-send-email-n-horiguchi@ah.jp.nec.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);