From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754202AbcFPLra (ORCPT ); Thu, 16 Jun 2016 07:47:30 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:34566 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562AbcFPLr1 (ORCPT ); Thu, 16 Jun 2016 07:47:27 -0400 Date: Thu, 16 Jun 2016 14:47:14 +0300 From: Ebru Akagunduz To: "Kirill A. Shutemov" , Hugh Dickins , Andrea Arcangeli , Andrew Morton Cc: Dave Hansen , Vlastimil Babka , Christoph Lameter , Naoya Horiguchi , Jerome Marchand , Yang Shi , Sasha Levin , Andres Lagar-Cavilla , Ning Qu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, sergey.senozhatsky.work@gmail.com Subject: Re: [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap_sem re-acquired Message-ID: <20160616114603.GA19710@gezgin> References: <1465222029-45942-1-git-send-email-kirill.shutemov@linux.intel.com> <1466021202-61880-1-git-send-email-kirill.shutemov@linux.intel.com> <1466021202-61880-6-git-send-email-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466021202-61880-6-git-send-email-kirill.shutemov@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Vlastimil noted[1] that pmd can be no longer valid after we drop 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 > --- > 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 >