Messages in this thread Patch in this message | | | From | Minchan Kim <> | Subject | [PATCH v2] thp: use is_zero_pfn only after pte_present check | Date | Tue, 13 Oct 2015 11:38:38 +0900 |
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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@vger.kernel.org> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Minchan Kim <minchan@kernel.org> --- Hello Greg,
This patch should go to -stable but when you will apply it after merging of linus tree, it will be surely conflicted due to userfaultfd part.
I want to know how to handle it.
Thanks.
mm/huge_memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 4b06b8db9df2..bbac913f96bc 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2206,7 +2206,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, 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 (!userfaultfd_armed(vma) && ++none_or_zero <= khugepaged_max_ptes_none) continue; -- 1.9.1
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