Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardownof hugetlbfs shared page tables V2 (resend)

[Michal Hocko]

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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