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SubjectRe: [PATCH v2] futex: Fix regression with read only mappings
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On Mon, 2011-06-27 at 11:40 -0500, Shawn Bohrer wrote:
> > > if (PageAnon(page_head)) {
> >
> > This bit needs a comment too (unless I am the only one to whom this
> was
> > non-obvious), maybe:
> >
> >
> > /*
> > * A read-only anonymous page implies a COW on a
> > * MAP_PRIVATE mapping. There is no sane use-case
> > * for this scenario, return -EFAULT to userspace.
> > */
>
> Your comment is wrong. Unfortunately the code is completly
> non-obvious to me as well, and I have no idea why it is there. This
> little snippet came from Peter's suggested fix in:
>
> https://lkml.org/lkml/2011/6/6/368
>
> Sadly Peter's gone silent and I'm left wondering if he knew some
> corner case that should return -EFAULT with a RO anonymous page or if
> he _thought_ this was preventing RO MAP_PRIVATE mappings. If it is
> the latter then this block can be removed because it does NOT do that.
> > > + if (ro) {
> > > + err = -EFAULT;
> > > + goto out;
> > > + }
> > > +

Peter simply gets too much email.. anyway, the reason I put that there
is that a RO Anon page will never change and is thus a little pointless
to use for futex ops.




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