Page migration issue with UBIFS

[Christoph Hellwig]

On Tue, Mar 15, 2016 at 04:32:40PM +0100, Richard Weinberger wrote:
> > Or if ->page_mkwrite() was called, why the page is not dirty?
> 
> BTW: UBIFS does not implement ->migratepage(), could this be a problem?

This might be the reason.  I can't reall make sense of
buffer_migrate_page, but it seems to migrate buffer_head state to
the new page.

I'd love to know why CMA even tries to migrate pages that don't have a
->migratepage method, this seems incredibly dangerous to me.