On 27.08.22 10:36, John Hubbard wrote:
> pin_user_page() is an externally-usable version of try_grab_page(), but
> with semantics that match get_page(), so that it can act as a drop-in
> replacement for get_page(). Specifically, pin_user_page() has a void
> return type.
>
> pin_user_page() elevates a page's refcount using FOLL_PIN rules. This
> means that the caller must release the page via unpin_user_page().
>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
> include/linux/mm.h | 1 +
> mm/gup.c | 33 +++++++++++++++++++++++++++++++++
> 2 files changed, 34 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 982f2607180b..85a105157334 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1869,6 +1869,7 @@ long pin_user_pages_remote(struct mm_struct *mm,
> long get_user_pages(unsigned long start, unsigned long nr_pages,
> unsigned int gup_flags, struct page **pages,
> struct vm_area_struct **vmas);
> +void pin_user_page(struct page *page);
> long pin_user_pages(unsigned long start, unsigned long nr_pages,
> unsigned int gup_flags, struct page **pages,
> struct vm_area_struct **vmas);
> diff --git a/mm/gup.c b/mm/gup.c
> index 5abdaf487460..245ccb41ed8c 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -3213,6 +3213,39 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
> }
> EXPORT_SYMBOL(pin_user_pages);
>
> +/**
> + * pin_user_page() - apply a FOLL_PIN reference to a page
> + *
> + * @page: the page to be pinned.
> + *
> + * This is similar to get_user_pages(), except that the page's refcount is
> + * elevated using FOLL_PIN, instead of FOLL_GET.
> + *
> + * IMPORTANT: The caller must release the page via unpin_user_page().
> + *
> + */
> +void pin_user_page(struct page *page)
> +{
> + struct folio *folio = page_folio(page);
> +
> + WARN_ON_ONCE(folio_ref_count(folio) <= 0);
> +
We should warn if the page is anon and !exclusive.
I assume the intend is to use pin_user_page() only to duplicate pins, right?
--
Thanks,
David / dhildenb
