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    SubjectRe: [PATCH v4 13/13] mincore: apply page table walker on do_mincore()
    On Wed, Jul 09, 2014 at 04:34:36PM +0300, Kirill A. Shutemov wrote:
    > On Tue, Jul 01, 2014 at 01:07:31PM -0400, Naoya Horiguchi wrote:
    > > This patch makes do_mincore() use walk_page_vma(), which reduces many lines
    > > of code by using common page table walk code.
    > >
    > > ChangeLog v4:
    > > - remove redundant vma
    > >
    > > ChangeLog v3:
    > > - add NULL vma check in mincore_unmapped_range()
    > > - don't use pte_entry()
    > >
    > > ChangeLog v2:
    > > - change type of args of callbacks to void *
    > > - move definition of mincore_walk to the start of the function to fix compiler
    > > warning
    > >
    > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    >
    > Trinity crases this implementation of mincore pretty easily:
    >
    > [ 42.775369] BUG: unable to handle kernel paging request at ffff88007bb61000
    > [ 42.776656] IP: [<ffffffff81126f8f>] mincore_unmapped_range+0xdf/0x100

    Thanks for your testing/reporting.

    ...
    >
    > Looks like 'vec' overflow. I don't see what could prevent do_mincore() to
    > write more than PAGE_SIZE to 'vec'.

    I found the miscalculation of walk->private (vec) on thp and hugetlbfs.
    I confirmed that the reported problem is fixed (I checked that trinity
    never triggers the reported BUG) with the following changes on this patch.

    diff --git a/mm/mincore.c b/mm/mincore.c
    index 3c64dcbcb3e2..9eb10d867a6f 100644
    --- a/mm/mincore.c
    +++ b/mm/mincore.c
    @@ -34,7 +34,7 @@ static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
    present = pte && !huge_pte_none(huge_ptep_get(pte));
    for (; addr != end; vec++, addr += PAGE_SIZE)
    *vec = present;
    - walk->private += (end - addr) >> PAGE_SHIFT;
    + walk->private = vec;
    #else
    BUG();
    #endif
    @@ -118,8 +118,10 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
    return 0;
    }

    - if (pmd_trans_unstable(pmd))
    + if (pmd_trans_unstable(pmd)) {
    + walk->private += (end - addr) >> PAGE_SHIFT;
    return 0;
    + }

    ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
    for (; addr != end; ptep++, addr += PAGE_SIZE) {
    Thanks,
    Naoya Horiguchi


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