ext4 stable page writes question

[Dmitry Monakhov <dmonakhov@openvz.org>]

According to stable write assumptions (1d1d1a767206fb)
grab_cache_page_write_begin() now calls relaxed method wait_for_stable_page()
which will wait for writeback to finish only if bdi demand that.
Commit message states that ext4 may not wait
But there are a lot of write-paths where we expect that:
BUG_ON(!PageLocked(page));
BUG_ON(PageWriteback(page));
And the only reason we avoid this bugon is because of commit 47564bfb95b
which use following trick to avoid lock inversion over journal_start:
page = grab_cache_page_write_begin()
unlock_page(page);
ext4_journal_start()
lock_page(page);
wait_on_page_writeback(page); <<<< unconditional wait

So as far as I understand this was done just by occasion because
ext4_page_mkwrite() use wait_for_stable_page().

So here is my question:  Do we have to wait for page's writeback to
finish for all write paths in ext4 code or we may use
wait_for_stable_page() and should cleanup all places where 
we may trigger BUG_ON(PageWriteback(page));