Re: [PATCH 12/16] mm/migration: fix potential page refcounts leak in migrate_pages

[Miaohe Lin <linmiaohe@huawei.com>]

On 2022/3/7 14:00, Baolin Wang wrote:
> 
> 
> On 3/7/2022 1:02 PM, Huang, Ying wrote:
>> Baolin Wang <baolin.wang@linux.alibaba.com> writes:
>>
>>> Hi Miaohe,
>>>
>>> On 3/4/2022 5:34 PM, Miaohe Lin wrote:
>>>> In -ENOMEM case, there might be some subpages of fail-to-migrate THPs
>>>> left in thp_split_pages list. We should move them back to migration
>>>> list so that they could be put back to the right list by the caller
>>>> otherwise the page refcnt will be leaked here. Also adjust nr_failed
>>>> and nr_thp_failed accordingly to make vm events account more accurate.
>>>> Fixes: b5bade978e9b ("mm: migrate: fix the return value of
>>>> migrate_pages()")
>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>>> ---
>>>>    mm/migrate.c | 9 +++++++++
>>>>    1 file changed, 9 insertions(+)
>>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>>> index e0db06927f02..6c2dfed2ddb8 100644
>>>> --- a/mm/migrate.c
>>>> +++ b/mm/migrate.c
>>>> @@ -1422,6 +1422,15 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>>                    }
>>>>                      nr_failed_pages += nr_subpages;
>>>> +                /*
>>>> +                 * There might be some subpages of fail-to-migrate THPs
>>>> +                 * left in thp_split_pages list. Move them back to migration
>>>> +                 * list so that they could be put back to the right list by
>>>> +                 * the caller otherwise the page refcnt will be leaked.
>>>> +                 */
>>>> +                list_splice_init(&thp_split_pages, from);
>>>> +                nr_failed += retry;
>>>> +                nr_thp_failed += thp_retry;
>>>
>>> Yes, I think we missed this case before, and your patch looks
>>> right. But we should also update the 'rc' to return the correct number
>>> of pages that were not migrated, right?
>>
>> Per my understanding, -ENOMEM should be returned to indicate an fatal
>> error.
>>
> 
> Ah, right. Sorry for noise.
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Oh, I missed this email. So we should return -ENOMEM in this case. Many thanks for both of you.

> .