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    SubjectRe: [PATCH] -mm swsusp: copy_page is harmfull

    On Mon, 2004-10-04 at 09:50, Benjamin Herrenschmidt wrote:
    > On Sat, 2004-09-25 at 10:27, Linux Kernel Mailing List wrote:
    > > ChangeSet 1.1983.1.3, 2004/09/24 17:27:41-07:00,
    > >
    > > [PATCH] -mm swsusp: copy_page is harmfull
    > >
    > > From: Pavel Machek <>
    > >
    > > This is my fault from long time ago: copy_page can't be used for copying
    > > task struct, therefore we can't use it in swsusp.
    > Hi !
    > Just curious, but why ?
    > It would be useful to have this in platform code, I don't see why I couldn't
    > use copy_page() on ppc and I suspect it will be more efficient than memcpy
    > since it has specific optimisations due to the fact that we are known to be
    > fully aligned and the size of the copy is a constant aligned power of 2.

    I think I can answer that one, seeing as Pavel seems to be asleep at the
    mo :>.

    On x86 at least (perhaps your platform is different), copy_page can
    resolve to different implementations. If you have 3D_NOW, the preempt
    count will be incremented prior to copying the page via a fpu_begin
    call. Sooner or later in doing the atomic copy of memory, you'll be
    copying the page containing the preempt count (the task struct) for the
    process doing the suspending. At that stage, you'll copy the preempt
    count being one too high, and at resume time it will still be one too
    high (we definitely can't use copy_page then). The simple solution would
    be to use copy_page and have something like

    #ifdef 3D_NOW

    But I'm sure you'll agree that even if it's faster, it's less clear and



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