3.14-rc2 XFS backtrace because irqs_disabled.

[Dave Jones]

On Fri, Feb 14, 2014 at 11:24:27AM +1100, Dave Chinner wrote:
 
 > > I can fix this one easily - we already have a workqueue for doing
 > > async log pushes (will split the stack between xlog_cil_force_lsn
 > > and xlog_cil_push), but the reason we haven't used it for synchronous
 > > log forces is that screws up fsync performance on CFQ. We don't
 > > recommend CFQ with XFS anyway, so I think I'll make this change
 > > anyway.
 > 
 > Dave, the patch below should chop off the stack usage from
 > xfs_log_force_lsn() issuing IO by deferring it to the CIL workqueue.
 > Can you given this a run?

Looks like it's survived an overnight run..

	Dave