mm/page-writeback.c: fix __set_page_dirty_no_writeback() return value

__set_page_dirty_no_writeback() should return true if it actually
transitioned the page from a clean to dirty state although it seems nobody
uses its return value at present.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Acked-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b5d8a1f..28763b8 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1103,7 +1103,7 @@
 int __set_page_dirty_no_writeback(struct page *page)
 {
 	if (!PageDirty(page))
-		SetPageDirty(page);
+		return !TestSetPageDirty(page);
 	return 0;
 }