Re: [PATCH 14/16] mm/migration: fix potential invalid node access for reclaim-based migration

[Huang, Ying]

Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:

> On 3/4/2022 5:34 PM, Miaohe Lin wrote:
>> If we failed to setup hotplug state callbacks for mm/demotion:online in
>> some corner cases, node_demotion will be left uninitialized. Invalid node
>> might be returned from the next_demotion_node() when doing reclaim-based
>> migration. Use kcalloc to allocate node_demotion to fix the issue.
>> Fixes: ac16ec835314 ("mm: migrate: support multiple target nodes
>> demotion")
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>>   mm/migrate.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 279940c0c064..7b1c0b988234 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -2516,9 +2516,9 @@ static int __init migrate_on_reclaim_init(void)
>>   {
>>   	int ret;
>>   -	node_demotion = kmalloc_array(nr_node_ids,
>> -				      sizeof(struct demotion_nodes),
>> -				      GFP_KERNEL);
>> +	node_demotion = kcalloc(nr_node_ids,
>> +				sizeof(struct demotion_nodes),
>> +				GFP_KERNEL);
>
> Nit: not sure if this is worthy of this rare corner case, but I think
> the target demotion nodes' default value should be NUMA_NO_NODE
> instead of 0.

The "nr" field of "struct demotion_nodes" should be initialized as 0.  I
think that is checked before "nodes[]" field.

Best Regards,
Huang, Ying