xfs i_lock vs mmap_sem lockdep trace.

[Al Viro]

On Mon, Mar 31, 2014 at 10:43:35AM +1100, Dave Chinner wrote:
> filldir on a directory inode vs page fault on regular file. Known
> issue, definitely a false positive. We have to change locking
> algorithms to avoid such deficiencies of lockdep (a case of "lockdep
> considered harmful", perhaps?) so it's not something I'm about to
> rush...

Give i_lock on directories a separate class, as it's been done for i_mutex...