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Date: Wed, 2 Apr 2008 15:06:19 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Andrea Arcangeli <andrea@qumranet.com>
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Subject: Re: EMM: Require single threadedness for registration.
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On Thu, 3 Apr 2008, Andrea Arcangeli wrote:

> That would work for #v10 if I remove the invalidate_range_start from
> try_to_unmap_cluster, it can't work for EMM because you've
> emm_invalidate_start firing anywhere outside the context of the
> current task (even regular rmap code, not just nonlinear corner case
> will trigger the race). In short the single threaded approach would be

But in that case it will be firing for a callback to another mm_struct. 
The notifiers are bound to mm_structs and keep separate contexts.

> The requirement for invalidate_page is that the pte and linux tlb are
> flushed _before_ and the page is freed _after_ the invalidate_page
> method. that's not the case for _begin/_end. The page is freed well
> before _end runs, hence the need of _begin and to block the secondary
> mmu page fault during the vma-mangling operations.

You could flush in _begin and free on _end? I thought you are taking a 
refcount on the page? You can drop the refcount only on _end to ensure 
that the page does not go away before.