From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756318AbaAHMmp (ORCPT ); Wed, 8 Jan 2014 07:42:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:52929 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755610AbaAHMml (ORCPT ); Wed, 8 Jan 2014 07:42:41 -0500 Date: Wed, 8 Jan 2014 13:42:40 +0100 From: Michal Hocko To: Bob Liu Cc: Sasha Levin , Wanpeng Li , Naoya Horiguchi , Bob Liu , Linux-MM , LKML Subject: Re: could you clarify mm/mempolicy: fix !vma in new_vma_page() Message-ID: <20140108124240.GH27937@dhcp22.suse.cz> References: <20140106112422.GA27602@dhcp22.suse.cz> <20140106141827.GB27602@dhcp22.suse.cz> <20140107102212.GC8756@dhcp22.suse.cz> <20140107173034.GE8756@dhcp22.suse.cz> <20140108100859.GC27937@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 08-01-14 20:09:30, Bob Liu wrote: > On Wed, Jan 8, 2014 at 6:08 PM, Michal Hocko wrote: > > > > > If I was debugging this I would simply add printk into page_address_in_vma > > error paths. > > > > Anyway, I think that at least hugetlbfs part should be reverted because > > it might paper over real bugs. Although the migration would fail for > > such hugetlb page we should catch that a weird page was tried to be > > migrated. What about the patch below? > > Looks good to me. But we need to confirm whether our assumption is right. Which assumption you have in mind? non-linear mapping or failing on anon_vma or f_mapping checks? > Sasha, could you please have a test with Michal's patch? I obviously doesn't have anything against testing but we should really focus on the original issue. This patch simply restores hugetlb code path. > Thanks, > -Bob > > > --- > > From 2d61421f26a3b63b4670d71b7adc67e2191b6157 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko > > Date: Wed, 8 Jan 2014 10:57:41 +0100 > > Subject: [PATCH] mm: new_vma_page cannot see NULL vma for hugetlb pages > > > > 11c731e81bb0 (mm/mempolicy: fix !vma in new_vma_page()) has removed > > BUG_ON(!vma) from new_vma_page which is partially correct because > > page_address_in_vma will return EFAULT for non-linear mappings and at > > least shared shmem might be mapped this way. > > > > The patch also tried to prevent NULL ptr for hugetlb pages which is not > > correct AFAICS because hugetlb pages cannot be mapped as VM_NONLINEAR > > and other conditions in page_address_in_vma seem to be legit and catch > > real bugs. > > > > This patch restores BUG_ON for PageHuge to catch potential issues when > > the to-be-migrated page is not setup properly. > > > > Signed-off-by: Michal Hocko > > --- > > mm/mempolicy.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > index 9e8d2d86978a..f3f51464a23b 100644 > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -1199,10 +1199,8 @@ static struct page *new_vma_page(struct page *page, unsigned long private, int * > > } > > > > if (PageHuge(page)) { > > - if (vma) > > - return alloc_huge_page_noerr(vma, address, 1); > > - else > > - return NULL; > > + BUG_ON(vma) > > + return alloc_huge_page_noerr(vma, address, 1); > > } > > /* > > * if !vma, alloc_page_vma() will use task or system default policy > > -- > > 1.8.5.2 > > > > -- > > Michal Hocko > > SUSE Labs -- Michal Hocko SUSE Labs