[PATCH] splice: fix bugs with stealing regular pipe pages

- Check that page has suitable count for stealing in the regular pipes.
- pipe_to_file() assumes that the page is locked on succesful steal, so
  do that in the pipe steal hook
- Missing unlock_page() in add_to_page_cache() failure.

Signed-off-by: Jens Axboe <axboe@suse.de>

fs/pipe.c

@@ -127,8 +127,15 @@ static void anon_pipe_buf_unmap(struct pipe_inode_info *pipe,
 static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
 			       struct pipe_buffer *buf)
 {
-	buf->flags |= PIPE_BUF_FLAG_STOLEN;
-	return 0;
+	struct page *page = buf->page;
+
+	if (page_count(page) == 1) {
+		buf->flags |= PIPE_BUF_FLAG_STOLEN;
+		lock_page(page);
+		return 0;
+	}
+
+	return 1;
 }
 
 static void anon_pipe_buf_get(struct pipe_inode_info *info,