Messages in this thread | | | Date | Wed, 8 Jan 2014 21:10:29 +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 8:42 PM, Michal Hocko <mhocko@suse.cz> wrote: > On Wed 08-01-14 20:09:30, Bob Liu wrote: >> 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. > > Which assumption you have in mind? non-linear mapping or failing on > anon_vma or f_mapping checks? >
The assumption that the original BUG_ON(!vma) was triggered by non-linear mapping.
>> 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
Oh, I see your point. Yes, I agree that your patch should be merged and if the BUG_ON() is triggered(which is unlikely) again. We can open another thread and analysis the root cause.
>> > --- >> > 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>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
>> > --- >> > 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 >> >
-- Regards, --Bob
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