linux-kernel - Re: [PATCH] mm: hugetlb: undo change to page mapcount in fault handler

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Message-Id: <20120110124558.a7303493.akpm@linux-foundation.org>
Date:	Tue, 10 Jan 2012 12:45:58 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] mm: hugetlb: undo change to page mapcount in fault
 handler

On Wed, 4 Jan 2012 15:16:32 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Fri, 23 Dec 2011 21:00:41 +0800
> Hillf Danton <dhillf@...il.com> wrote:
> 
> > Page mapcount should be updated only if we are sure that the page ends
> > up in the page table otherwise we would leak if we couldn't COW due to
> > reservations or if idx is out of bounds.
> 
> It would be much nicer if we could run vma_needs_reservation() before
> even looking up or allocating the page.
> 
> And afaict the interface is set up to do that: you run
> vma_needs_reservation() before allocating the page and then
> vma_commit_reservation() afterwards.
> 
> But hugetlb_no_page() and hugetlb_fault() appear to have forgotten to
> run vma_commit_reservation() altogether.  Why isn't this as busted as
> it appears to be?

ping?
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