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    SubjectRe: BUG: about flush TLB during unmapping a page in memory subsystem
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    From: "yunfeng zhang" <zyf.zeroos@gmail.com>
    Date: Fri, 20 Oct 2006 10:47:49 +0800

    > In rmap.c::try_to_unmap_one of 2.6.16.29, there are some code snippets
    >
    > .....
    > /* Nuke the page table entry. */
    > flush_cache_page(vma, address, page_to_pfn(page));
    > pteval = ptep_clear_flush(vma, address, pte);
    > // >>> The above line is expanded as below
    > // >>> pte_t __pte;
    > // >>> __pte = ptep_get_and_clear((__vma)->vm_mm, __address, __ptep);
    > // >>> flush_tlb_page(__vma, __address);
    > // >>> __pte;
    >
    > /* Move the dirty bit to the physical page now the pte is gone. */
    > if (pte_dirty(pteval))
    > set_page_dirty(page);
    > .....
    >
    >
    > It seems that they only can work on UP system.
    >
    > On SMP, let's suppose the pte was clean, after A CPU executed
    > ptep_get_and_clear,
    > B CPU makes the pte dirty, which will make a fatal error to A CPU since it gets
    > a stale pte, isn't right?

    B can't make it dirty because it's been cleared to zero
    and flush_tlb_page() has removed the TLB cached copy of
    the PTE. B can therefore only see the new cleared PTE.
    -
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