linux-kernel - Re: page allocator regression on nommu

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Date:	Tue, 01 Sep 2009 16:48:43 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	David Howells <dhowells@...hat.com>
Cc:	Paul Mundt <lethal@...ux-sh.org>, Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: page allocator regression on nommu

On Tue, 2009-09-01 at 14:46 +0100, David Howells wrote:
> From: David Howells <dhowells@...hat.com>
> Subject: [PATCH] NOMMU: Fix error handling in do_mmap_pgoff()
> 
> Fix the error handling in do_mmap_pgoff().  If do_mmap_shared_file() or
> do_mmap_private() fail, we jump to the error_put_region label at which point we
> cann __put_nommu_region() on the region - but we haven't yet added the region
> to the tree, and so __put_nommu_region() may BUG because the region tree is
> empty or it may corrupt the region tree.
> 
> To get around this, we can afford to add the region to the region tree before
> calling do_mmap_shared_file() or do_mmap_private() as we keep nommu_region_sem
> write-locked, so no-one can race with us by seeing a transient region.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>

Looks sane to me. FWIW:

Acked-by: Pekka Enberg <penberg@...helsinki.fi>

			Pekka

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