New code for 5.10: - Don't WARN_ON weird states that unprivileged users can create. - Don't invalidate page cache when direct writes want to fall back to buffered. - Fix some problems when readahead ios fail. - Fix a problem where inline data pages weren't getting flushed during an unshare operation. - Rework iomap to support arbitrarily many blocks per page in preparation to support THP for the page cache. - Fix a bug in the blocksize < pagesize buffered io path where we could fail to initialize the many-blocks-per-page uptodate bitmap correctly when the backing page is actually up to date. This could cause us to forget to write out dirty pages.