Re: [PATCH v2] thp: use is_zero_pfn only after pte_present check

[Minchan Kim]

On Tue, Oct 13, 2015 at 09:28:23AM +0200, Vlastimil Babka wrote:
> On 10/13/2015 04:38 AM, Minchan Kim wrote:
> >Use is_zero_pfn on pteval only after pte_present check on pteval
> >(It might be better idea to introduce is_zero_pte where checks
> >pte_present first). Otherwise, it could work with swap or
> >migration entry and if pte_pfn's result is equal to zero_pfn
> >by chance, we lose user's data in __collapse_huge_page_copy.
> >So if you're luck, the application is segfaulted and finally you
> >could see below message when the application is exit.
> >
> >BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
> >
> >Cc: <stable@xxxxxxxxxxxxxxx>
> 
> More specific:
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.1+
> Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent
> huge pages")
> 
> >Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Thanks for the detail and review, Vlastimil.
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