Re: [PATCH -v8 3/4] Enable the MS_ASYNC functionality in sys_msync()

[Matt Mackall <mpm@selenic.com>]

On Thu, 2008-01-24 at 12:36 +1100, Nick Piggin wrote:
> On Thursday 24 January 2008 04:05, Linus Torvalds wrote:
> > On Wed, 23 Jan 2008, Anton Salikhmetov wrote:
> > > +
> > > +		if (pte_dirty(*pte) && pte_write(*pte)) {
> >
> > Not correct.
> >
> > You still need to check "pte_present()" before you can test any other
> > bits. For a non-present pte, none of the other bits are defined, and for
> > all we know there might be architectures out there that require them to
> > be non-dirty.
> >
> > As it is, you just possibly randomly corrupted the pte.
> >
> > Yeah, on all architectures I know of, it the pte is clear, neither of
> > those tests will trigger, so it just happens to work, but it's still
> > wrong.
> 
> Probably it can fail for !present nonlinear mappings on many
> architectures.

Definitely.

-- 
Mathematics is the supreme nostalgia of our time.

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