Re: oops in copy_page_rep()

[Hugh Dickins]

On Tue, 8 Jan 2013, Andrea Arcangeli wrote:
> 
> Looking at this, one thing that isn't clear is where the page_count is
> checked in migrate_misplaced_transhuge_page. Ok that it's unable to
> migrate anon transhuge COW shared pages so it doesn't need to mess
> with rmap (the mapcount check makes it safe), but it shouldn't be
> allowed to migrate memory that has gup direct-IO in flight (and that
> can only be detected with a page_count vs mapcount check). Real
> migrate does page_freeze_refs to be safe. Mel comments?

Yes, I protested to Mel about that before the holidays, and he
quickly provided a patch, now in akpm's tree; but checking it again
today, I believe it's still not quite right yet - see other mail.

Hugh
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