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Date: Thu, 16 Jun 2016 14:47:14 +0300 From: Ebru Akagunduz <ebru.akagunduz@...il.com> To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Hugh Dickins <hughd@...gle.com>, Andrea Arcangeli <aarcange@...hat.com>, Andrew Morton <akpm@...ux-foundation.org> Cc: Dave Hansen <dave.hansen@...el.com>, Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...two.org>, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, Jerome Marchand <jmarchan@...hat.com>, Yang Shi <yang.shi@...aro.org>, Sasha Levin <sasha.levin@...cle.com>, Andres Lagar-Cavilla <andreslc@...gle.com>, Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, sergey.senozhatsky.work@...il.com Subject: Re: [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap_sem re-acquired On Wed, Jun 15, 2016 at 11:06:10PM +0300, Kirill A. Shutemov wrote: > Vlastimil noted[1] that pmd can be no longer valid after we drop > mmap_sem. We need recheck it once mmap_sem taken again. > > [1] http://lkml.kernel.org/r/12918dcd-a695-c6f4-e06f-69141c5f357f@suse.cz > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> > --- > mm/huge_memory.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index d7ccc8558187..0efdad975659 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2437,6 +2437,9 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > /* vma is no longer available, don't continue to swapin */ > if (hugepage_vma_revalidate(mm, address)) > return false; > + /* check if the pmd is still valid */ > + if (mm_find_pmd(mm, address) != pmd) > + return false; > } Thanks for fixing this. > if (ret & VM_FAULT_ERROR) { > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0); > @@ -2522,6 +2525,9 @@ static void collapse_huge_page(struct mm_struct *mm, > result = hugepage_vma_revalidate(mm, address); > if (result) > goto out; > + /* check if the pmd is still valid */ > + if (mm_find_pmd(mm, address) != pmd) > + goto out; > However here, I don't know do we need to check pmd. Because in collapse_huge_page; pmd is newly created, after taking mmap_sem read: { pmd_t *pmd, _pmd; pte_t *pte; ... down_read(&mm->mmap_sem); result = hugepage_vma_revalidate(mm, address); ... pmd = mm_find_pmd(mm, address); ... Therefore it did not seem like a problem for me. > anon_vma_lock_write(vma->anon_vma); > > -- > 2.8.1 >
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