Provide a helper in the get_user_pages code to drop a pin or a ref on a
page based on being given FOLL_GET or FOLL_PIN in its flags argument or do
nothing if neither is set.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@lst.de>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
---
  include/linux/mm.h |  3 +++
  mm/gup.c           | 22 ++++++++++++++++++++++
  2 files changed, 25 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8f857163ac89..3de9d88f8524 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -1367,6 +1367,9 @@ static inline bool is_cow_mapping(vm_flags_t flags)
  #define SECTION_IN_PAGE_FLAGS
  #endif
  
+void folio_put_unpin(struct folio *folio, unsigned int flags);
+void page_put_unpin(struct page *page, unsigned int flags);

+
  /*
   * The identification function is mainly used by the buddy allocator for
   * determining if two pages could be buddies. We are not really identifying

diff --git a/mm/gup.c b/mm/gup.c
index f45a3a5be53a..3ee4b4c7e0cb 100644
--- a/mm/gup.c
+++ b/mm/gup.c

@@ -191,6 +191,28 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
  		folio_put_refs(folio, refs);
  }
  
+/**
+ * folio_put_unpin - Unpin/put a folio as appropriate
+ * @folio: The folio to release
+ * @flags: gup flags indicating the mode of release (FOLL_*)
+ *
+ * Release a folio according to the flags.  If FOLL_GET is set, the folio has a
+ * ref dropped; if FOLL_PIN is set, it is unpinned; otherwise it is left
+ * unaltered.
+ */
+void folio_put_unpin(struct folio *folio, unsigned int flags)
+{
+	if (flags & (FOLL_GET | FOLL_PIN))