Re: [PATCH] mm: do not use page_count without a page pin

[Minchan Kim]

Hi Wanpeng,

On 06/11/2012 09:23 AM, Wanpeng Li wrote:

> On Mon, Jun 11, 2012 at 09:17:51AM +0900, Minchan Kim wrote:
>> d179e84ba fixed the problem[1] in vmscan.c but same problem is here.
>> Let's fix it.
>>
>> [1] http://comments.gmane.org/gmane.linux.kernel.mm/65844
>>
>> I copy and paste d179e84ba's contents for description.
>>
>> "It is unsafe to run page_count during the physical pfn scan because
>> compound_head could trip on a dangling pointer when reading
>> page->first_page if the compound page is being freed by another CPU."
>>
>> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>> Cc: Mel Gorman <mgorman@xxxxxxx>
>> Cc: Michal Hocko <mhocko@xxxxxxx>
>> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
>> ---
>> mm/page_alloc.c |    6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 266f267..019c4fe 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5496,7 +5496,11 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
>> 			continue;
>>
>> 		page = pfn_to_page(check);
>> -		if (!page_count(page)) {
>> +		/*
>> +		 * We can't use page_count withou pin a page
>                                         ^
> 										without


I will resend fixed version after reviewer comment out.
Thanks!

-- 
Kind regards,
Minchan Kim
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