From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f177.google.com (mail-ve0-f177.google.com [209.85.128.177]) by kanga.kvack.org (Postfix) with ESMTP id 21FC16B0035 for ; Wed, 8 Jan 2014 07:09:32 -0500 (EST) Received: by mail-ve0-f177.google.com with SMTP id db12so1160998veb.22 for ; Wed, 08 Jan 2014 04:09:31 -0800 (PST) Received: from mail-ve0-x233.google.com (mail-ve0-x233.google.com [2607:f8b0:400c:c01::233]) by mx.google.com with ESMTPS id e7si781569qez.36.2014.01.08.04.09.30 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 08 Jan 2014 04:09:30 -0800 (PST) Received: by mail-ve0-f179.google.com with SMTP id jw12so1176990veb.10 for ; Wed, 08 Jan 2014 04:09:30 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20140108100859.GC27937@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> Date: Wed, 8 Jan 2014 20:09:30 +0800 Message-ID: Subject: Re: could you clarify mm/mempolicy: fix !vma in new_vma_page() From: Bob Liu Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Sasha Levin Cc: Wanpeng Li , Naoya Horiguchi , Bob Liu , Linux-MM , LKML 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. Sasha, could you please have a test with Michal's patch? 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org