Re: [PATCH v2 09/11] mm/migration: fix potential page refcounts leak in migrate_pages

[Feng Tang]

> 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.
 
We just met a real world case for this when checking a malloc-oom
issue and our fix is similar with yours :).

So I think you can remove the 'potential' from the patch subject.
Feel free to add

Tested-by: Feng Tang <feng.tang@xxxxxxxxx>
Reviewed-by: Feng Tang <feng.tang@xxxxxxxxx>

Thanks,
Feng

> Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
>  mm/migrate.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 63a87ef0996f..97dfd1f4870d 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1438,6 +1438,14 @@ 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_thp_failed += thp_retry;
>  				goto out;
>  			case -EAGAIN:
>  				if (is_thp)
> -- 
> 2.23.0