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Date: Wed, 2 Apr 2008 14:54:52 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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Subject: Re: [patch 1/9] EMM Notifier: The notifier calls
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On Wed, 2 Apr 2008, Andrea Arcangeli wrote:

> > Hmmm... Okay that is one solution that would just require a BUG_ON in the 
> > registration methods.
> 
> Perhaps you didn't notice that this solution can't work if you call
> range_begin/end not in the "current" context and try_to_unmap_cluster
> does exactly that for both my patchset and yours. Missing an _end is
> ok, missing a _begin is never ok.

If you look at the patch you will see a requirement of holding a 
writelock on mmap_sem which will keep out get_user_pages().