linux-kernel - Re: [PATCH] mm: fix invalid use of pfn_valid_within in test_pages_in_a

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Date:	Wed, 10 Dec 2014 09:01:26 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	James Custer <jcuster@....com>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>
CC:	<rja@....com>, <dfults@....com>
Subject: Re: [PATCH] mm: fix invalid use of pfn_valid_within in test_pages_in_a_zone

(2014/12/10 4:34), James Custer wrote:
> Offlining memory by 'echo 0 > /sys/devices/system/memory/memory#/online'
> or reading valid_zones 'cat /sys/devices/system/memory/memory#/valid_zones'

> causes BUG: unable to handle kernel paging request due to invalid use of
> pfn_valid_within. This is due to a bug in test_pages_in_a_zone.

The information is not enough to understand what happened on your system.
Could you show full BUG messages?

> 
> In order to use pfn_valid_within within a MAX_ORDER_NR_PAGES block of pages,
> a valid pfn within the block must first be found. There only needs to be
> one valid pfn found in test_pages_in_a_zone in the first place. So the
> fix is to replace pfn_valid_within with pfn_valid such that the first
> valid pfn within the pageblock is found (if it exists). This works
> independently of CONFIG_HOLES_IN_ZONE.
> 
> Signed-off-by: James Custer <jcuster@....com>
> ---
>   mm/memory_hotplug.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1bf4807..304c187 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1331,7 +1331,7 @@ int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
>   }
>   
>   /*
> - * Confirm all pages in a range [start, end) is belongs to the same zone.
> + * Confirm all pages in a range [start, end) belong to the same zone.
>    */
>   int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
>   {
> @@ -1342,10 +1342,11 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
>   	for (pfn = start_pfn;
>   	     pfn < end_pfn;
>   	     pfn += MAX_ORDER_NR_PAGES) {

> -		i = 0;
> -		/* This is just a CONFIG_HOLES_IN_ZONE check.*/
> -		while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i))
> -			i++;
> +		/* Find the first valid pfn in this pageblock */
> +		for (i = 0; i < MAX_ORDER_NR_PAGES; i++) {
> +			if (pfn_valid(pfn + i))
> +				break;
> +		}

If CONFIG_HOLES_IN_NODE is set, there is no difference. Am I making a mistake?

Thanks,
Yasuaki Ishimatsu


>   		if (i == MAX_ORDER_NR_PAGES)
>   			continue;
>   		page = pfn_to_page(pfn + i);
> 


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