1 files changed, 33 insertions, 34 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3b3e3b8bb706..3dc3a8c2c485 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -356,36 +356,50 @@ static inline struct page *compound_head(struct page *page)
         return page;
 }
 
+/*
+ * The atomic page->_mapcount, starts from -1: so that transitions
+ * both from it and to it can be tracked, using atomic_inc_and_test
+ * and atomic_add_negative(-1).
+ */
+static inline void reset_page_mapcount(struct page *page)
+{
+        atomic_set(&(page)->_mapcount, -1);
+}
+
+static inline int page_mapcount(struct page *page)
+{
+        return atomic_read(&(page)->_mapcount) + 1;
+}
+
 static inline int page_count(struct page *page)
 {
         return atomic_read(&compound_head(page)->_count);
 }
 
+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);
+}
+
+extern bool __get_page_tail(struct page *page);
+
 static inline void get_page(struct page *page)
 {
+        if (unlikely(PageTail(page)))
+                if (likely(__get_page_tail(page)))
+                        return;
         /*
          * Getting a normal page or the head of a compound page
-         * requires to already have an elevated page->_count. Only if
-         * we're getting a tail page, the elevated page->_count is
-         * required only in the head page, so for tail pages the
-         * bugcheck only verifies that the page->_count isn't
-         * negative.
+         * requires to already have an elevated page->_count.
          */
-        VM_BUG_ON(atomic_read(&page->_count) < !PageTail(page));
+        VM_BUG_ON(atomic_read(&page->_count) <= 0);
         atomic_inc(&page->_count);
-        /*
-         * Getting a tail page will elevate both the head and tail
-         * page->_count(s).
-         */
-        if (unlikely(PageTail(page))) {
-                /*
-                 * This is safe only because
-                 * __split_huge_page_refcount can't run under
-                 * get_page().
-                 */
-                VM_BUG_ON(atomic_read(&page->first_page->_count) <= 0);
-                atomic_inc(&page->first_page->_count);
-        }
 }
 
 static inline struct page *virt_to_head_page(const void *x)
@@ -804,21 +818,6 @@ static inline pgoff_t page_index(struct page *page)
 }
 
 /*
- * The atomic page->_mapcount, like _count, starts from -1:
- * so that transitions both from it and to it can be tracked,
- * using atomic_inc_and_test and atomic_add_negative(-1).
- */
-static inline void reset_page_mapcount(struct page *page)
-{
-        atomic_set(&(page)->_mapcount, -1);
-}
-
-static inline int page_mapcount(struct page *page)
-{
-        return atomic_read(&(page)->_mapcount) + 1;
-}
-
-/*
  * Return true if this page is mapped into pagetables.
  */
 static inline int page_mapped(struct page *page)