3.10-stable review patch. If anyone has any objections, please let me know.
------------------ From: "Kirill A. Shutemov" <[email protected]> commit ee53664bda169f519ce3c6a22d378f0b946c8178 upstream. Sasha Levin found a NULL pointer dereference that is due to a missing page table lock, which in turn is due to the pmd entry in question being a transparent huge-table entry. The code - introduced in commit 1998cc048901 ("mm: make madvise(MADV_WILLNEED) support swap file prefetch") - correctly checks for this situation using pmd_none_or_trans_huge_or_clear_bad(), but it turns out that that function doesn't work correctly. pmd_none_or_trans_huge_or_clear_bad() expected that pmd_bad() would trigger if the transparent hugepage bit was set, but it doesn't do that if pmd_numa() is also set. Note that the NUMA bit only gets set on real NUMA machines, so people trying to reproduce this on most normal development systems would never actually trigger this. Fix it by removing the very subtle (and subtly incorrect) expectation, and instead just checking pmd_trans_huge() explicitly. Reported-by: Sasha Levin <[email protected]> Acked-by: Andrea Arcangeli <[email protected]> [ Additionally remove the now stale test for pmd_trans_huge() inside the pmd_bad() case - Linus ] Signed-off-by: Linus Torvalds <[email protected]> Cc: Wang Long <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- include/asm-generic/pgtable.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -550,11 +550,10 @@ static inline int pmd_none_or_trans_huge #ifdef CONFIG_TRANSPARENT_HUGEPAGE barrier(); #endif - if (pmd_none(pmdval)) + if (pmd_none(pmdval) || pmd_trans_huge(pmdval)) return 1; if (unlikely(pmd_bad(pmdval))) { - if (!pmd_trans_huge(pmdval)) - pmd_clear_bad(pmd); + pmd_clear_bad(pmd); return 1; } return 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
