Re: [linux-next-20160602] kernel BUG at mm/rmap.c:1253!

[Vlastimil Babka <vbabka@suse.cz>]

On 06/02/2016 03:13 PM, Michal Hocko wrote:
> On Thu 02-06-16 13:59:49, Michal Hocko wrote:
>> [CCing Ebru]
>>
>> On Thu 02-06-16 13:50:46, Michal Hocko wrote:
>>> [CCing Andrea and Kirill]
>>
>> Hmm, thinking about it little bit more it might be related to "mm, thp:
>> make swapin readahead under down_read of mmap_sem". I didn't get to look
>> closer at the patch but maybe revalidate after mmap sem is dropped is
>> not sufficient.
>
> so hugepage_vma_revalidate does this:
>
> 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
> 	hend = vma->vm_end & HPAGE_PMD_MASK;
> 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
> 		return SCAN_ADDRESS_RANGE;
>
> I really do not see why we have to play with hstart and hend.

AFAIU the point of these tests is to see whether the vma is large enough 
to contain the given address within a huge page. And it kind of silently 
assumes that address is already huge-page aligned.

> But
> address + HPAGE_PMD_SIZE > hend part looks suspicious. address
> always have to vm_start <= address && address < vm_end AFAICS.

I think the check is fine after a deeper look. The code itself is also 
quite old, the recent patches just abstracted it to the new function.

> and the above allows address + HPAGE_PMD_MASK == end.
>

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