linux-kernel - Re: [PATCH RESEND] memory hotplug: fix a double register section info bug

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Date:	Fri, 14 Sep 2012 20:00:09 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	qiuxishi <qiuxishi@...il.com>
CC:	<akpm@...ux-foundation.org>, <mgorman@...e.de>,
	<tony.luck@...el.com>, Jiang Liu <jiang.liu@...wei.com>,
	<qiuxishi@...wei.com>, <bessel.wang@...wei.com>,
	<wujianguo@...wei.com>, <paul.gortmaker@...driver.com>,
	<kamezawa.hiroyu@...fujitsu.com>, <kosaki.motohiro@...fujitsu.com>,
	<rientjes@...gle.com>, Minchan Kim <minchan@...nel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	Wen Congyang <wency@...fujitsu.com>
Subject: Re: [PATCH RESEND] memory hotplug: fix a double register section
 info bug

HiXishi,

2012/09/14 12:43, qiuxishi wrote:
> There may be a bug when registering section info. For example, on
> my Itanium platform, the pfn range of node0 includes the other nodes,
> so other nodes' section info will be double registered, and memmap's
> page count will equal to 3.
>
> node0: start_pfn=0x100,    spanned_pfn=0x20fb00, present_pfn=0x7f8a3, => 0x000100-0x20fc00
> node1: start_pfn=0x80000,  spanned_pfn=0x80000,  present_pfn=0x80000, => 0x080000-0x100000
> node2: start_pfn=0x100000, spanned_pfn=0x80000,  present_pfn=0x80000, => 0x100000-0x180000
> node3: start_pfn=0x180000, spanned_pfn=0x80000,  present_pfn=0x80000, => 0x180000-0x200000
>
> free_all_bootmem_node()
> 	register_page_bootmem_info_node()
> 		register_page_bootmem_info_section()
>
> When hot remove memory, we can't free the memmap's page because
> page_count() is 2 after put_page_bootmem().
>
> sparse_remove_one_section()
> 	free_section_usemap()
> 		free_map_bootmem()
> 			put_page_bootmem()
>
> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> ---
>   mm/memory_hotplug.c |   10 ++++------
>   1 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 2adbcac..cf493c7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -126,9 +126,6 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)
>   	struct mem_section *ms;
>   	struct page *page, *memmap;
>
> -	if (!pfn_valid(start_pfn))
> -		return;
> -
>   	section_nr = pfn_to_section_nr(start_pfn);
>   	ms = __nr_to_section(section_nr);
>
> @@ -187,9 +184,10 @@ void register_page_bootmem_info_node(struct pglist_data *pgdat)
>   	end_pfn = pfn + pgdat->node_spanned_pages;
>
>   	/* register_section info */
> -	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION)
> -		register_page_bootmem_info_section(pfn);
> -
> +	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> +		if (pfn_valid(pfn) && (pfn_to_nid(pfn) == node))

I cannot judge whether your configuration is correct or not.
Thus if it is correct, I want a comment of why the node check is
needed. In usual configuration, a node does not span the other one.
So it is natural that "pfn_to_nid(pfn) is same as "pgdat->node_id".
Thus we may remove the node check in the future.

Thanks,
Yasuaki Ishimatsu

> +			register_page_bootmem_info_section(pfn);
> +	}
>   }
>   #endif /* !CONFIG_SPARSEMEM_VMEMMAP */
>


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