The patch below does not apply to the 3.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From cbef8478bee55775ac312a574aad48af7bb9cf9f Mon Sep 17 00:00:00 2001 From: Naoya Horiguchi <[email protected]> Date: Wed, 11 Feb 2015 15:25:19 -0800 Subject: [PATCH] mm/hugetlb: pmd_huge() returns true for non-present hugepage Migrating hugepages and hwpoisoned hugepages are considered as non-present hugepages, and they are referenced via migration entries and hwpoison entries in their page table slots. This behavior causes race condition because pmd_huge() doesn't tell non-huge pages from migrating/hwpoisoned hugepages. follow_page_mask() is one example where the kernel would call follow_page_pte() for such hugepage while this function is supposed to handle only normal pages. To avoid this, this patch makes pmd_huge() return true when pmd_none() is true *and* pmd_present() is false. We don't have to worry about mixing up non-present pmd entry with normal pmd (pointing to leaf level pte entry) because pmd_present() is true in normal pmd. The same race condition could happen in (x86-specific) gup_pmd_range(), where this patch simply adds pmd_present() check instead of pmd_huge(). This is because gup_pmd_range() is fast path. If we have non-present hugepage in this function, we will go into gup_huge_pmd(), then return 0 at flag mask check, and finally fall back to the slow path. Fixes: 290408d4a2 ("hugetlb: hugepage migration core") Signed-off-by: Naoya Horiguchi <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: James Hogan <[email protected]> Cc: David Rientjes <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Luiz Capitulino <[email protected]> Cc: Nishanth Aravamudan <[email protected]> Cc: Lee Schermerhorn <[email protected]> Cc: Steve Capper <[email protected]> Cc: <[email protected]> [2.6.36+] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index d7547824e763..224b14235e96 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -172,7 +172,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, */ if (pmd_none(pmd) || pmd_trans_splitting(pmd)) return 0; - if (unlikely(pmd_large(pmd))) { + if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) { /* * NUMA hinting faults need to be handled in the GUP * slowpath for accounting purposes and so that they diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c index f48423f10141..42982b26e32b 100644 --- a/arch/x86/mm/hugetlbpage.c +++ b/arch/x86/mm/hugetlbpage.c @@ -54,9 +54,15 @@ int pud_huge(pud_t pud) #else +/* + * pmd_huge() returns 1 if @pmd is hugetlb related entry, that is normal + * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry. + * Otherwise, returns 0. + */ int pmd_huge(pmd_t pmd) { - return !!(pmd_val(pmd) & _PAGE_PSE); + return !pmd_none(pmd) && + (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT; } int pud_huge(pud_t pud) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f533d336e569..d96b8bfa748f 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3679,6 +3679,8 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, { struct page *page; + if (!pmd_present(*pmd)) + return NULL; page = pte_page(*(pte_t *)pmd); if (page) page += ((address & ~PMD_MASK) >> PAGE_SHIFT); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
