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    Subject[PATCH 2/4] powerpc: get_hugepte() don't put_page() the wrong page
    "page" may have changed to point to the next hugepage after the loop
    completed, The references have been taken on the head page, so the
    put_page must happen there too.

    This is a longstanding issue pre-thp inclusion.

    It's totally unclear how these page_cache_add_speculative and
    pte_val(pte) != pte_val(*ptep) checks are necessary across all the
    powerpc gup_fast code, when x86 doesn't need any of that: there's no way
    the page can be freed with irq disabled so we're guaranteed the
    atomic_inc will happen on a page with page_count > 0 (so not needing the
    speculative check). The pte check is also meaningless on x86: no need to
    rollback on x86 if the pte changed, because the pte can still change a
    CPU tick after the check succeeded and it won't be rolled back in that
    case. The important thing is we got a reference on a valid page that was
    mapped there a CPU tick ago. So not knowing the soft tlb refill code of
    ppc64 in great detail I'm not removing the "speculative" page_count
    increase and the pte checks across all the code, but unless there's a
    strong reason for it they should be later cleaned up too.

    If a pte can change from huge to non-huge (like it could happen with
    THP) passing a pte_t *ptep to gup_hugepte() would also require to repeat
    the is_hugepd in gup_hugepte(), but that shouldn't happen with hugetlbfs
    only so I'm not altering that.

    Signed-off-by: Andrea Arcangeli <>

    diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
    index 0b9a5c1..b649c28 100644
    --- a/arch/powerpc/mm/hugetlbpage.c
    +++ b/arch/powerpc/mm/hugetlbpage.c
    @@ -429,7 +429,7 @@ static noinline int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long add
    if (unlikely(pte_val(pte) != pte_val(*ptep))) {
    /* Could be optimized better */
    while (*nr) {
    - put_page(page);
    + put_page(head);

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      Last update: 2011-10-16 22:43    [W:0.043 / U:4.476 seconds]
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