linux-kernel - Re: [PATCH 2/2] mm/sparsemem: Fix a bug in free_map_bootmem when CONFIG_SPARSEMEM

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Date:	Sun, 06 Oct 2013 00:45:45 +0800
From:	Zhang Yanfei <zhangyanfei.yes@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Wen Congyang <wency@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Toshi Kani <toshi.kani@...com>, isimatu.yasuaki@...fujitsu.com,
	Linux MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] mm/sparsemem: Fix a bug in free_map_bootmem when
 CONFIG_SPARSEMEM_VMEMMAP

Hello andrew,

On 10/04/2013 04:42 AM, Andrew Morton wrote:
> On Thu, 03 Oct 2013 11:32:02 +0800 Zhang Yanfei <zhangyanfei.yes@...il.com> wrote:
> 
>> We pass the number of pages which hold page structs of a memory
>> section to function free_map_bootmem. This is right when
>> !CONFIG_SPARSEMEM_VMEMMAP but wrong when CONFIG_SPARSEMEM_VMEMMAP.
>> When CONFIG_SPARSEMEM_VMEMMAP, we should pass the number of pages
>> of a memory section to free_map_bootmem.
>>
>> So the fix is removing the nr_pages parameter. When
>> CONFIG_SPARSEMEM_VMEMMAP, we directly use the prefined marco
>> PAGES_PER_SECTION in free_map_bootmem. When !CONFIG_SPARSEMEM_VMEMMAP,
>> we calculate page numbers needed to hold the page structs for a
>> memory section and use the value in free_map_bootmem.
> 
> What were the runtime user-visible effects of that bug?
> 
> Please always include this information when fixing a bug.


Sorry....This was found by reading the code. And I have no machine that
support memory hot-remove to test the bug now. But I believe it is a bug.

BTW, I've made a mistake in this patch which was found by wanpeng. I'll
send v2.

-- 
Thanks.
Zhang Yanfei
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