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SubjectRe: [PATCH 14/16] mm/migration: fix potential invalid node access for reclaim-based migration
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On 3/7/2022 1:14 PM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@linux.alibaba.com> 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@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.
>
> The "nr" field of "struct demotion_nodes" should be initialized as 0. I
> think that is checked before "nodes[]" field.

Right, but it will be confusing that if nr = 0, while the nodes[] still
contains valid node id 0. While we are at this, why not initialize the
node_demotion structure with a clear default value? Anyway, no strong
opinion on this :)

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