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Date: Thu, 11 Oct 2012 10:00:29 +0900 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, alan@...rguk.ukuu.org.uk, Andrea Arcangeli <aarcange@...hat.com>, Rik van Riel <riel@...hat.com>, Johannes Weiner <jweiner@...hat.com>, Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: [ 077/120] mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andrea Arcangeli <aarcange@...hat.com> commit 027ef6c87853b0a9df53175063028edb4950d476 upstream. In many places !pmd_present has been converted to pmd_none. For pmds that's equivalent and pmd_none is quicker so using pmd_none is better. However (unless we delete pmd_present) we should provide an accurate pmd_present too. This will avoid the risk of code thinking the pmd is non present because it's under __split_huge_page_map, see the pmd_mknotpresent there and the comment above it. If the page has been mprotected as PROT_NONE, it would also lead to a pmd_present false negative in the same way as the race with split_huge_page. Because the PSE bit stays on at all times (both during split_huge_page and when the _PAGE_PROTNONE bit get set), we could only check for the PSE bit, but checking the PROTNONE bit too is still good to remember pmd_present must always keep PROT_NONE into account. This explains a not reproducible BUG_ON that was seldom reported on the lists. The same issue is in pmd_large, it would go wrong with both PROT_NONE and if it races with split_huge_page. Signed-off-by: Andrea Arcangeli <aarcange@...hat.com> Acked-by: Rik van Riel <riel@...hat.com> Cc: Johannes Weiner <jweiner@...hat.com> Cc: Hugh Dickins <hughd@...gle.com> Cc: Mel Gorman <mgorman@...e.de> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- arch/x86/include/asm/pgtable.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -146,8 +146,7 @@ static inline unsigned long pmd_pfn(pmd_ static inline int pmd_large(pmd_t pte) { - return (pmd_flags(pte) & (_PAGE_PSE | _PAGE_PRESENT)) == - (_PAGE_PSE | _PAGE_PRESENT); + return pmd_flags(pte) & _PAGE_PSE; } #ifdef CONFIG_TRANSPARENT_HUGEPAGE @@ -415,7 +414,13 @@ static inline int pte_hidden(pte_t pte) static inline int pmd_present(pmd_t pmd) { - return pmd_flags(pmd) & _PAGE_PRESENT; + /* + * Checking for _PAGE_PSE is needed too because + * split_huge_page will temporarily clear the present bit (but + * the _PAGE_PSE flag will remain set at all times while the + * _PAGE_PRESENT bit is clear). + */ + return pmd_flags(pmd) & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PSE); } static inline int pmd_none(pmd_t pmd) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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