[PATCH] splice: fix double page unlock

If add_to_page_cache_lru() fails, the page will not be locked. But
splice jumps to an error path that does a page release and unlock,
causing a BUG() in unlock_page().

Fix this by adding one more label that just releases the page. This bug
was actually triggered on EL5 by gurudas pai <gurudas.pai@oracle.com>
using fio.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

fs/splice.c

@@ -614,7 +614,7 @@ static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 			ret = add_to_page_cache_lru(page, mapping, index,
 						    GFP_KERNEL);
 			if (unlikely(ret))
-				goto out;
+				goto out_release;
 		}
 
 		/*
@@ -695,8 +695,9 @@ static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 		goto find_page;
 	}
 out:
-	page_cache_release(page);
 	unlock_page(page);
+out_release:
+	page_cache_release(page);
 out_ret:
 	return ret;
 }