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

[Bob Liu <bob.liu@oracle.com>]

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?

-- 
Regards,
-Bob

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