3.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> commit cbef8478bee55775ac312a574aad48af7bb9cf9f upstream. 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 <n-horiguchi@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: James Hogan <james.hogan@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Mel Gorman <mel@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx> Cc: Nishanth Aravamudan <nacc@xxxxxxxxxxxxxxxxxx> Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx> Cc: Steve Capper <steve.capper@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/gup.c | 2 +- arch/x86/mm/hugetlbpage.c | 8 +++++++- mm/hugetlb.c | 2 ++ 3 files changed, 10 insertions(+), 2 deletions(-) --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -172,7 +172,7 @@ static int gup_pmd_range(pud_t pud, unsi */ 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 --- a/arch/x86/mm/hugetlbpage.c +++ b/arch/x86/mm/hugetlbpage.c @@ -66,9 +66,15 @@ follow_huge_addr(struct mm_struct *mm, u return ERR_PTR(-EINVAL); } +/* + * 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) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3666,6 +3666,8 @@ follow_huge_pmd(struct mm_struct *mm, un { 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html