Re: mm: kernel BUG at mm/mempolicy.c:1203!

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Tue, Dec 17, 2013 at 01:11:23AM -0500, Naoya Horiguchi wrote:
>Hello Bob,
>
>On Tue, Dec 17, 2013 at 12:38:49PM +0800, Bob Liu wrote:
>> On 12/17/2013 09:10 AM, Sasha Levin wrote:
>> > On 12/16/2013 07:44 PM, Bob Liu wrote:
>> >>
>> >> On 12/16/2013 07:37 AM, Sasha Levin wrote:
>> >>> Hi all,
>> >>>
>> >>> While fuzzing with trinity inside a KVM tools guest running latest -next
>> >>> kernel, I've
>> >>> stumbled on the following spew.
>> >>>
>> >>> This seems to be due to commit 0bf598d863e "mbind: add BUG_ON(!vma) in
>> >>> new_vma_page()"
>> >>> which added that BUG_ON.
>> >>
>> >> Could you take a try with this patch from Wanpeng Li?
>> >>
>> >> Thanks,
>> >> -Bob
>> >>
>> >> Subject: [PATCH] mm/mempolicy: fix !vma in new_vma_page()
>> >> ....
>> >> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>> >> index eca4a31..73b5a35 100644
>> >> --- a/mm/mempolicy.c
>> >> +++ b/mm/mempolicy.c
>> >> @@ -1197,14 +1197,16 @@ static struct page *new_vma_page(struct page
>> >> *page, unsigned long private, int *
>> >>               break;
>> >>           vma = vma->vm_next;
>> >>       }
>> >> +
>> >> +    if (PageHuge(page)) {
>> >> +        if (vma)
>> >> +            return alloc_huge_page_noerr(vma, address, 1);
>> >> +        else
>> >> +            return NULL;
>> >> +    }
>> >>       /*
>> >> -     * queue_pages_range() confirms that @page belongs to some vma,
>> >> -     * so vma shouldn't be NULL.
>> >> +     * if !vma, alloc_page_vma() will use task or system default policy
>> >>        */
>> >> -    BUG_ON(!vma);
>> >> -
>> >> -    if (PageHuge(page))
>> >> -        return alloc_huge_page_noerr(vma, address, 1);
>> >>       return alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
>> >>   }
>> >>   #else
>> >>
>> > 
>> > Hmm... So in essence it's mostly a revert of Naoya's patch, who seemed
>> > pretty certain that this
>> > situation shouldn't happen at all. What's the reasoning behind just
>> 
>> I think this assumption may not correct.
>> Even if
>> address = __vma_address(page, vma);
>> and
>> vma->start < address < vma->end;
>> page_address_in_vma() may still return -EFAULT because of many other
>> conditions in it.
>> As a result the while loop in new_vma_page() may end with vma=NULL.
>> 
>> Naoya, any idea?
>
>Yes, you totally make sense. So please apply Wanpeng's patch.
>

Ah, ok, I will send a formalized patch. 

Regards,
Wanpeng Li 

>Thanks,
>Naoya Horiguchi
>
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