Re: [PATCH] mm/gup: stop leaking pinned pages in low memory conditions

John Hubbard
2024-10-17T17:06:56Z

On 10/17/24 1:53 AM, David Hildenbrand wrote:
> On 17.10.24 10:51, David Hildenbrand wrote:
>> On 16.10.24 22:22, John Hubbard wrote:
...
> And staring at memfd_pin_folios(), don't we have the same issue there if
> check_and_migrate_movable_folios() fails?

Yes, it looks very clearly like the exact same bug, in a different location.
This complicated return code is the gift that keeps on giving. Although
likely people are just copying the pattern, which had the problem.

>
> diff --git a/mm/gup.c b/mm/gup.c
> index a82890b46a36..f79974d38608 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -3708,12 +3708,10 @@ long memfd_pin_folios(struct file *memfd, loff_t
> start, loff_t end,
>                 ret = check_and_migrate_movable_folios(nr_folios, folios);
>         } while (ret == -EAGAIN);
>
> -       memalloc_pin_restore(flags);
> -       return ret ? ret : nr_folios;
>  err:
>         memalloc_pin_restore(flags);
> -       unpin_folios(folios, nr_folios);
> -
> -       return ret;
> +       if (ret)
> +               unpin_folios(folios, nr_folios);
> +       return ret ? ret : nr_folios;

That looks correct. I can send this out with the other patch as a tiny
2-patch series since they are related. Would you prefer to appear
as a Signed-off-by, or a Suggested-by, or "other"? :)

>  }
>  EXPORT_SYMBOL_GPL(memfd_pin_folios);
>
>

thanks,
--
John Hubbard