From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754267AbcFPLwm (ORCPT ); Thu, 16 Jun 2016 07:52:42 -0400 Received: from mail-lf0-f66.google.com ([209.85.215.66]:33338 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754217AbcFPLwj (ORCPT ); Thu, 16 Jun 2016 07:52:39 -0400 Date: Thu, 16 Jun 2016 14:51:54 +0300 From: "Kirill A. Shutemov" To: Ebru Akagunduz Cc: "Kirill A. Shutemov" , Hugh Dickins , Andrea Arcangeli , Andrew Morton , 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: <20160616115154.GE18137@node.shutemov.name> 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> <20160616114603.GA19710@gezgin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160616114603.GA19710@gezgin> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 16, 2016 at 02:47:14PM +0300, Ebru Akagunduz wrote: > 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 Vlastimil noted[1] that pmd can be no longer valid after we drop 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. I guess you're looking on the first hugepage_vma_revalidate() in collapse_huge_page(). The patch fixes issue after the second one: pmd_t *pmd, _pmd; pte_t *pte; ... down_read(&mm->mmap_sem); result = hugepage_vma_revalidate(mm, address); ... pmd = mm_find_pmd(mm, address); ... up_read(&mm->mmap_sem); ... down_write(&mm->mmap_sem); result = hugepage_vma_revalidate(mm, address); if (mm_find_pmd(mm, address) != pmd) goto out; -- Kirill A. Shutemov