Re: Does GUP page unpinning have to be done in the pinning context?

[John Hubbard <jhubbard@nvidia.com>]

On 4/4/25 3:29 AM, David Hildenbrand wrote:
> On 04.04.25 12:20, David Howells wrote:
>> Hi Kirill, John, David,
> 
> Hi,
> 
>>
>> I don't know if you're the experts on GUP, but can you tell me if 
>> unpinning,
>> e.g. unpin_user_page(), needs to be done in the same MM context and/or 
>> the
>> same user context as the initial pinning?  And, if so, is there some 
>> way to
>> break that link?
> 
> gup_put_folio() seems to only rely on per-folio information (esp. 
> node_stat_mod_folio).
> 
> So there should not be such a context requirement.

That is correct. The essence of gup/pup is that it operates on
struct pages, and doesn't have any "moral" connection to higher
layers or additional process context.


thanks,
-- 
John Hubbard