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);
+
+ /*
+ * Similar to try_grab_page(): be sure to *also*
+ * increment the normal page refcount field at least once,
+ * so that the page really is pinned.
+ */
+ if (folio_test_large(folio)) {
+ folio_ref_add(folio, 1);
+ atomic_add(1, folio_pincount_ptr(folio));
+ } else {
+ folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
+ }
+
+ node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
+}
+EXPORT_SYMBOL(pin_user_page);
+
/*
* pin_user_pages_unlocked() is the FOLL_PIN variant of
* get_user_pages_unlocked(). Behavior is the same, except that this one sets
--
2.37.2
