Re: [PATCH] mm: fix invalid node in alloc_migrate_target()

[Xishi Qiu]

On 2016/3/26 3:22, Andrew Morton wrote:

> On Fri, 25 Mar 2016 14:56:04 +0800 Xishi Qiu <qiuxishi@xxxxxxxxxx> wrote:
> 
>> It is incorrect to use next_node to find a target node, it will
>> return MAX_NUMNODES or invalid node. This will lead to crash in
>> buddy system allocation.
>>
>> ...
>>
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -289,11 +289,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private,
>>  	 * now as a simple work-around, we use the next node for destination.
>>  	 */
>>  	if (PageHuge(page)) {
>> -		nodemask_t src = nodemask_of_node(page_to_nid(page));
>> -		nodemask_t dst;
>> -		nodes_complement(dst, src);
>> +		int node = next_online_node(page_to_nid(page));
>> +		if (node == MAX_NUMNODES)
>> +			node = first_online_node;
>>  		return alloc_huge_page_node(page_hstate(compound_head(page)),
>> -					    next_node(page_to_nid(page), dst));
>> +					    node);
>>  	}
>>  
>>  	if (PageHighMem(page))
> 
> Indeed.  Can you tell us more about this circumstances under which the
> kernel will crash?  I need to decide which kernel version(s) need the
> patch, but the changelog doesn't contain the info needed to make this
> decision (it should).
> 

Hi Andrew,

I read the code v4.4, and find the following path maybe trigger the bug.

alloc_migrate_target()
	alloc_huge_page_node()  // the node may be offline or MAX_NUMNODES
		__alloc_buddy_huge_page_no_mpol()
			__alloc_buddy_huge_page()
				__hugetlb_alloc_buddy_huge_page()
					alloc_pages_node()
						__alloc_pages_node()
							VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
							VM_WARN_ON(!node_online(nid));

Thanks,
Xishi Qiu