Re: could you clarify mm/mempolicy: fix !vma in new_vma_page()

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

Cced Sasha,
On Tue, Jan 07, 2014 at 12:26:13PM +0800, Wanpeng Li wrote:
>Hi Michal,
>On Mon, Jan 06, 2014 at 03:18:27PM +0100, Michal Hocko wrote:
>>On Mon 06-01-14 20:45:54, Bob Liu wrote:
>>[...]
>>>  544         if (PageAnon(page)) {
>>>  545                 struct anon_vma *page__anon_vma = page_anon_vma(page);
>>>  546                 /*
>>>  547                  * Note: swapoff's unuse_vma() is more efficient with this
>>>  548                  * check, and needs it to match anon_vma when KSM is active.
>>>  549                  */
>>>  550                 if (!vma->anon_vma || !page__anon_vma ||
>>>  551                     vma->anon_vma->root != page__anon_vma->root)
>>>  552                         return -EFAULT;
>>>  553         } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
>>>  554                 if (!vma->vm_file ||
>>>  555                     vma->vm_file->f_mapping != page->mapping)
>>>  556                         return -EFAULT;
>>>  557         } else
>>>  558                 return -EFAULT;
>>> 
>>> That's the "other conditions" and the reason why we can't use
>>> BUG_ON(!vma) in new_vma_page().
>>
>>Sorry, I wasn't clear with my question. I was interested in which of
>>these triggered and why only for hugetlb pages?
>
>Not just for hugetlb pages, sorry for do two things in one patch. The change 
>for hugetlb pages is to fix the potential dereference NULL pointer reported 
>by Dan. http://marc.info/?l=linux-mm&m=137689530323257&w=2 
>
>If we should ask Sasha to add more debug information to dump which condition 
>is failed in page_address_in_vma() for you?
>
>Regards,
>Wanpeng Li 
>	
>
>>
>>-- 
>>Michal Hocko
>>SUSE Labs
>
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