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

[Baolin Wang <baolin.wang@linux.alibaba.com>]

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@huawei.com>
> ---
>   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.