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

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

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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