| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.2 107/110] thp: use is_zero_pfn() only after pte_present() check | Date | Fri, 6 Nov 2015 11:19:54 -0800 |
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4.2-stable review patch. If anyone has any objections, please let me know.
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From: Minchan Kim <minchan@kernel.org>
commit 47aee4d8e314384807e98b67ade07f6da476aa75 upstream.
Use is_zero_pfn() on pteval only after pte_present() check on pteval (It might be better idea to introduce is_zero_pte() which checks pte_present() first).
Otherwise when working on a 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 unlucky, the application segfaults and finally you could see below message on exit:
BUG: Bad rss-counter state mm:ffff88007f099300 idx:2 val:3
Fixes: ca0984caa823 ("mm: incorporate zero pages into transparent huge pages") Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/huge_memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2132,7 +2132,8 @@ static int __collapse_huge_page_isolate( for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++, address += PAGE_SIZE) { pte_t pteval = *_pte; - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { + if (pte_none(pteval) || (pte_present(pteval) && + is_zero_pfn(pte_pfn(pteval)))) { if (++none_or_zero <= khugepaged_max_ptes_none) continue; else
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