current->sched_class->yield_task is NULL, any hint?

[Peter Zijlstra]

On Wed, Apr 09, 2014 at 10:43:32AM -0700, Lin Ming wrote:
> Hi Peter,
> 
> I hit a panic in sys_sched_yield() because(for some unknown reason)
> current->sched_class->yield_task is NULL.
> It's an ARM embedded board with 3.4-rt kernel.
> 
> Could you share any hint for the possible causes?

What class does current->sched_class point to?