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    Subject[PATCH 3.2 33/46] mm/huge_memory: replace VM_NO_THP VM_BUG_ON with actual VMA check
    3.2.81-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Konstantin Khlebnikov <koct9i@gmail.com>

    commit 3486b85a29c1741db99d0c522211c82d2b7a56d0 upstream.

    Khugepaged detects own VMAs by checking vm_file and vm_ops but this way
    it cannot distinguish private /dev/zero mappings from other special
    mappings like /dev/hpet which has no vm_ops and popultes PTEs in mmap.

    This fixes false-positive VM_BUG_ON and prevents installing THP where
    they are not expected.

    Link: http://lkml.kernel.org/r/CACT4Y+ZmuZMV5CjSFOeXviwQdABAgT7T+StKfTqan9YDtgEi5g@mail.gmail.com
    Fixes: 78f11a255749 ("mm: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups")
    Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Acked-by: Vlastimil Babka <vbabka@suse.cz>
    Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    [bwh: Backported to 3.2:
    - The assertions use VM_BUG_ON() and also check is_linear_pfn_mapping();
    keep that check
    - Adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    mm/huge_memory.c | 6 ++----
    1 file changed, 2 insertions(+), 4 deletions(-)

    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1635,14 +1635,14 @@ int khugepaged_enter_vma_merge(struct vm
    * page fault if needed.
    */
    return 0;
    - if (vma->vm_ops)
    + if (vma->vm_ops || (vm_flags & VM_NO_THP))
    /* khugepaged not yet working on file or special mappings */
    return 0;
    /*
    * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
    * true too, verify it here.
    */
    - VM_BUG_ON(is_linear_pfn_mapping(vma) || vm_flags & VM_NO_THP);
    + VM_BUG_ON(is_linear_pfn_mapping(vma));
    hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
    hend = vma->vm_end & HPAGE_PMD_MASK;
    if (hstart < hend)
    @@ -1831,8 +1831,8 @@ static bool hugepage_vma_check(struct vm
    * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
    * true too, verify it here.
    */
    - VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);
    - return true;
    + VM_BUG_ON(is_linear_pfn_mapping(vma));
    + return !(vma->vm_flags & VM_NO_THP);
    }

    static void collapse_huge_page(struct mm_struct *mm,
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