Messages in this thread | | | Date | Wed, 8 Jan 2014 20:09:30 +0800 | Subject | Re: could you clarify mm/mempolicy: fix !vma in new_vma_page() | From | Bob Liu <> |
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On Wed, Jan 8, 2014 at 6:08 PM, Michal Hocko <mhocko@suse.cz> 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 <mhocko@suse.cz> > 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 <mhocko@suse.cz> > --- > 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
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