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    SubjectRe: [PATCH] Fix incorrect kunmap_atomic in pktcdvd
    Peter Osterlund <petero2@telia.com> wrote:
    >
    > Andrew Morton <akpm@osdl.org> writes:
    >
    > > Peter Osterlund <petero2@telia.com> wrote:
    > > >
    > > > The pktcdvd driver uses kunmap_atomic() incorrectly. The function is
    > > > supposed to take an address as the first parameter, but the pktcdvd
    > > > driver passed a page pointer. Thanks to Douglas Gilbert and Jens Axboe
    > > > for discovering this.
    > >
    > > You're about the 7,000th person to make that mistake. We really should
    > > catch it via typechecking but the code's really lame and nobody ever got
    > > around to rotorooting it.
    >
    > Why was the interface made different from kmap()/kunmap() in the first
    > place? Wouldn't it have made more sense to let kunmap_atomic() take a
    > page pointer as the first parameter?

    No, kmap-atomic() maps a single page into the CPU's address space by making
    a pte point at the page. To unmap that page we need to get at the pte, not
    at the page. If kmap_atomic() were to take a pageframe address we'd need
    to search the whole fixmap space for the corresponding page - a reverse
    lookup.


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