linux-kernel - Re: [patch 01/10] mm: bootmem: fix checking the bitmap when finally freeing bootmem

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Message-ID: <20120507180706.GD19417@google.com>
Date:	Mon, 7 May 2012 11:07:06 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	David Miller <davem@...emloft.net>,
	Yinghai Lu <yinghai@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 01/10] mm: bootmem: fix checking the bitmap when
 finally freeing bootmem

On Mon, May 07, 2012 at 01:37:43PM +0200, Johannes Weiner wrote:
> From: Gavin Shan <shangw@...ux.vnet.ibm.com>
> 
> When bootmem releases an unaligned chunk of memory at the beginning of
> a node to the page allocator, it iterates from that unaligned PFN but
> checks an aligned word of the page bitmap.  The checked bits do not
> correspond to the PFNs and, as a result, reserved pages can be freed.
> 
> Properly shift the bitmap word so that the lowest bit corresponds to
> the starting PFN before entering the freeing loop.
> 
> This bug has been around since 41546c1 "bootmem: clean up
> free_all_bootmem_core" (2.6.27) without known reports.
> 
> Signed-off-by: Gavin Shan <shangw@...ux.vnet.ibm.com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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