Re: Change in functionality of futex() system call.

[Peter Zijlstra]

On Mon, 2011-06-06 at 18:22 +0200, Eric Dumazet wrote:
> Le lundi 06 juin 2011 Ã 18:16 +0200, Peter Zijlstra a Ãcrit :
> 
> > Hmm, wouldn't that still be susceptible to the zero-page thing if: we
> > create a writable private file map of a sparse file, touch a page and
> > then remap the thing RO?
> > 
> > 
> > 
> 
> Also I am not sure how MAP_PRIVATE could be affected. If we still try a
> RW gup()... It will allocate a page for us, instead of still pointing to
> shared one.
> 
> On previous kernel, the application using read-only mapping could use
> MAP_PRIVATE or MAP_SHARED with same 'behavior'

But by not forcing the COW you get different behaviour depending on when
you call FUTEX_WAIT, surely that's not correct either?
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