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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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