[RFC v8 PATCH 13/20] memory-hotplug: check page type in get_page_bootmem

[Andrew Morton]

On Tue, 28 Aug 2012 18:00:20 +0800
wency at cn.fujitsu.com wrote:

> From: Yasuaki Ishimatsu <isimatu.yasuaki at jp.fujitsu.com>
> 
> There is a possibility that get_page_bootmem() is called to the same page many
> times. So when get_page_bootmem is called to the same page, the function only
> increments page->_count.

I really don't understand this explanation, even after having looked at
the code.  Can you please have another attempt at the changelog?

> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -95,10 +95,17 @@ static void release_memory_resource(struct resource *res)
>  static void get_page_bootmem(unsigned long info,  struct page *page,
>  			     unsigned long type)
>  {
> -	page->lru.next = (struct list_head *) type;
> -	SetPagePrivate(page);
> -	set_page_private(page, info);
> -	atomic_inc(&page->_count);
> +	unsigned long page_type;
> +
> +	page_type = (unsigned long) page->lru.next;
> +	if (page_type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
> +	    page_type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE){
> +		page->lru.next = (struct list_head *) type;
> +		SetPagePrivate(page);
> +		set_page_private(page, info);
> +		atomic_inc(&page->_count);
> +	} else
> +		atomic_inc(&page->_count);
>  }

And a code comment which explains what is going on would be good.  As
is always the case ;)