From c8c663e9cd6ba477d8fe5bb5708ed33d21985b03 Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Wed, 2 Nov 2011 13:37:15 -0700
Subject: [PATCH] --- yaml --- r: 273223 b: refs/heads/master c:
 3526741f0964c88bc2ce511e1078359052bf225b h: refs/heads/master i:   273221:
 ccf196e710585ff12fc5b1f1fb0d104b37d6713d   273219:
 7487a1d2447d904c2712d84f39f55f9babb47ff2   273215:
 208ef3be26f9eb5c91eb1266733a5c2cb7f729b7 v: v3

---
 [refs]                              |  2 +-
 trunk/arch/powerpc/mm/hugetlbpage.c | 24 +++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index 857e1e3e1813..286b1b98b387 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 8596468487e2062cae2aad56e973784e03959245
+refs/heads/master: 3526741f0964c88bc2ce511e1078359052bf225b
diff --git a/trunk/arch/powerpc/mm/hugetlbpage.c b/trunk/arch/powerpc/mm/hugetlbpage.c
index 78b14abded65..a618ef01bfad 100644
--- a/trunk/arch/powerpc/mm/hugetlbpage.c
+++ b/trunk/arch/powerpc/mm/hugetlbpage.c
@@ -385,12 +385,23 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	return NULL;
 }
 
+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);
+}
+
 static noinline int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 		       unsigned long end, int write, struct page **pages, int *nr)
 {
 	unsigned long mask;
 	unsigned long pte_end;
-	struct page *head, *page;
+	struct page *head, *page, *tail;
 	pte_t pte;
 	int refs;
 
@@ -413,6 +424,7 @@ static noinline int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long add
 	head = pte_page(pte);
 
 	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
+	tail = page;
 	do {
 		VM_BUG_ON(compound_head(page) != head);
 		pages[*nr] = page;
@@ -431,6 +443,16 @@ static noinline int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long add
 		*nr -= refs;
 		while (refs--)
 			put_page(head);
+	} else {
+		/*
+		 * Any tail page need their mapcount reference taken
+		 * before we return.
+		 */
+		while (refs--) {
+			if (PageTail(tail))
+				get_huge_page_tail(tail);
+			tail++;
+		}
 	}
 
 	return 1;