From: Fengguang Wu <wfg@mail.ustc.edu.cn>

We should first check (page!=NULL) before PageWriteback(page).

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/readahead.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff -puN mm/readahead.c~mm-share-pg_readahead-and-pg_reclaim-fix mm/readahead.c
--- a/mm/readahead.c~mm-share-pg_readahead-and-pg_reclaim-fix
+++ a/mm/readahead.c
@@ -439,11 +439,13 @@ page_cache_readahead_ondemand(struct add
 	if (!ra->ra_pages)
 		return 0;
 
-	/* It's PG_reclaim! */
-	if (PageWriteback(page))
-		return 0;
-
 	if (page) {
+		/*
+		 * It can be PG_reclaim.
+		 */
+		if (PageWriteback(page))
+			return 0;
+
 		ClearPageReadahead(page);
 
 		/*
_