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

[Michal Hocko <mhocko@kernel.org>]

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

and the above allows address + HPAGE_PMD_MASK == end.
-- 
Michal Hocko
SUSE Labs

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