3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrea Arcangeli <redacted>

commit e0d85a366c2300efd230ef82a9b22110b0658331 upstream.

Up to this point the code assumed old refcounting for hugepages (pre-thp).
 This updates the code directly to the thp mapcount tail page refcounting.

Signed-off-by: Andrea Arcangeli <redacted>
Cc: Peter Zijlstra <redacted>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <redacted>
Cc: Rik van Riel <redacted>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Gibson <redacted>
Cc: Martin Schwidefsky <redacted>
Cc: Heiko Carstens <redacted>
Acked-by: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 arch/sparc/mm/gup.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c

@@ -12,6 +12,17 @@
 #include <linux/rwsem.h>
 #include <asm/pgtable.h>
 
+static inline void get_huge_page_tail(struct page *page)
+{
+	/*
+	 * __split_huge_page_refcount() cannot run
+	 * from under us.
+	 */
+	VM_BUG_ON(page_mapcount(page) < 0);
+	VM_BUG_ON(atomic_read(&page->_count) != 0);
+	atomic_inc(&page->_mapcount);
+}
+
 /*
  * The performance critical leaf functions are made noinline otherwise gcc
  * inlines everything into a single function which results in too much

@@ -56,6 +67,8 @@ static noinline int gup_pte_range(pmd_t
 			put_page(head);
 			return 0;
 		}
+		if (head != page)
+			get_huge_page_tail(page);
 
 		pages[*nr] = page;
 		(*nr)++;