linux-kernel - Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)

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Date:	Fri, 27 Jul 2012 11:02:43 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Rik van Riel <riel@...hat.com>
Cc:	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	David Gibson <david@...son.dropbear.id.au>,
	Ken Chen <kenchen@...gle.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown
 of hugetlbfs shared page tables V2 (resend)

On Thu 26-07-12 14:31:50, Rik van Riel wrote:
> On 07/20/2012 10:36 AM, Michal Hocko wrote:
> 
> >--- a/arch/x86/mm/hugetlbpage.c
> >+++ b/arch/x86/mm/hugetlbpage.c
> >@@ -81,7 +81,12 @@ static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
> >  		if (saddr) {
> >  			spte = huge_pte_offset(svma->vm_mm, saddr);
> >  			if (spte) {
> >-				get_page(virt_to_page(spte));
> >+				struct page *spte_page = virt_to_page(spte);
> >+				if (!is_hugetlb_pmd_page_valid(spte_page)) {
> 
> What prevents somebody else from marking the hugetlb
> pmd invalid, between here...
> 
> >+					spte = NULL;
> >+					continue;
> >+				}
> 
> ... and here?

huge_ptep_get_and_clear is (should be) called inside i_mmap which is not
the case right now as Mel already pointed out in other email

-- 
Michal Hocko
SUSE Labs
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