The set_page_dirty() in the ext3_writepage() failure path isn't right.
set_page_dirty() will alter buffer states - it's a "whole page"
dirtying.

__set_page_dirty_buffers() is emitting warnings when it refuses to set
dirty a non-uptodate buffer against a partially-mapped page.

All we want to do in there is to move the page back onto
mapping->dirty_pages, without altering the state of its buffers.