Make sure not to access sched_fair fields before verifying it is
indeed a sched_fair task.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
CC: stable@kernel.org
LKML-Reference: <20091216170517.577998058@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>