tux3: Support mmap write: Check overflow of round_up(newsize, PAGE_SIZE)

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
diff --git a/fs/tux3/filemap_blocklib.c b/fs/tux3/filemap_blocklib.c
index 52807b6..f7d7864 100644
--- a/fs/tux3/filemap_blocklib.c
+++ b/fs/tux3/filemap_blocklib.c
@@ -813,10 +813,12 @@
 	 * truncate_inode_pages finishes, hence the second
 	 * unmap_mapping_range call must be made for correctness.
 	 */
-	unmap_mapping_range(mapping, holebegin, 0, 1);
+	if (newsize <= holebegin)	/* Check overflow */
+		unmap_mapping_range(mapping, holebegin, 0, 1);
 	/* FIXME: The buffer fork before invalidate. We should merge to
 	 * truncate_inode_pages_range() */
 	tux3_truncate_inode_pages_range(mapping, newsize, MAX_LFS_FILESIZE);
 	truncate_inode_pages(mapping, newsize);
-	unmap_mapping_range(mapping, holebegin, 0, 1);
+	if (newsize <= holebegin)	/* Check overflow */
+		unmap_mapping_range(mapping, holebegin, 0, 1);
 }