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

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Message-ID: <de9ff75c-0416-46ed-90fd-c8801bbdc8ef@nvidia.com>
Date: Thu, 17 Oct 2024 10:06:50 -0700
From: John Hubbard <jhubbard@...dia.com>
To: David Hildenbrand <david@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
 Alistair Popple <apopple@...dia.com>, Shigeru Yoshida <syoshida@...hat.com>,
 Jason Gunthorpe <jgg@...dia.com>, Minchan Kim <minchan@...nel.org>,
 Pasha Tatashin <pasha.tatashin@...een.com>
Subject: Re: [PATCH] mm/gup: stop leaking pinned pages in low memory
 conditions

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