linux-kernel - Re: oops in copy_page

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Date:	Tue, 8 Jan 2013 20:23:46 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: oops in copy_page_rep()

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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