Re: vDSO vs. mm : problems with ppc vdso

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2006-02-28 at 12:32 +0000, Hugh Dickins wrote:
> On Tue, 28 Feb 2006, Nick Piggin wrote:
> > 
> > You should be OK. VM_RESERVED itself is something of an anachronism
> > these days. If you're not getting your page from the page allocator
> > then you'll want to make sure each of their count, and mapcount is
> > reset before allowing them to be mapped.
> 
> Yes, it's fine that VM_RESERVED isn't set on it.
> But I don't understand your remarks about count and mapcount at all:
> perhaps you meant to say something else?

Ah thanks , I was worried there too ;)

> If I ignore what you actually said, and think of what problems there
> might be in that area, then yes, if the pages come from kernel memory
> (they do) rather than page allocator, we'd better make sure page_count
> starts above 0, so it doesn't go down to zero on last free from userspace:
> and indeed, Ben's vdso_init does a get_page on each to ensure that.

Yup, I took care of that and that part seems to work. I don't touch
mapcount at all.

Ben.


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