ufs_get_locked_page(): make sure we have buffer_heads

callers rely upon that, but find_lock_page() racing with attempt of
page eviction by memory pressure might have left us with
* try_to_free_buffers() successfully done
* __remove_mapping() failed, leaving the page in our mapping
* find_lock_page() returning an uptodate page with no
buffer_heads attached.

Signed-off-by: Al Viro <[e-mail]>

fs/ufs/util.c

···
 struct page *ufs_get_locked_page(struct address_space *mapping,
 				 pgoff_t index)
 {
-	struct page *page;
-
-	page = find_lock_page(mapping, index);
+	struct inode *inode = mapping->host;
+	struct page *page = find_lock_page(mapping, index);
 	if (!page) {
 		page = read_mapping_page(mapping, index, NULL);
 
···
 			printk(KERN_ERR "ufs_change_blocknr: "
 			       "read_mapping_page error: ino %lu, index: %lu\n",
 			       mapping->host->i_ino, index);
-			goto out;
+			return page;
 		}
 
 		lock_page(page);
···
 			/* Truncate got there first */
 			unlock_page(page);
 			put_page(page);
-			page = NULL;
-			goto out;
+			return NULL;
 		}
 
 		if (!PageUptodate(page) || PageError(page)) {
···
 
 			printk(KERN_ERR "ufs_change_blocknr: "
 			       "can not read page: ino %lu, index: %lu\n",
-			       mapping->host->i_ino, index);
+			       inode->i_ino, index);
 
-			page = ERR_PTR(-EIO);
+			return ERR_PTR(-EIO);
 		}
 	}
-out:
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 	return page;
 }