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

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Message-ID: <a5b32587-877b-4b04-bb85-cb4738f3b748@redhat.com>
Date: Thu, 17 Oct 2024 19:10:20 +0200
From: David Hildenbrand <david@...hat.com>
To: John Hubbard <jhubbard@...dia.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 17.10.24 19:06, John Hubbard wrote:
> 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"? :)

Suggested-by: please :)

-- 
Cheers,

David / dhildenb