John Kacur pointed out that the get_cpu_var used in net/sched/sch_generic.c
would trigger warnings. This was happing on a statistic variable and
by a softirq which is bound to a single thread.

John sent a patch that used local_irq_save which is a little bit of
overkill. This version uses preempt disable, but we still need to create
a preempt_disable_rt API that is only activated when PREEMPT_RT is configured.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>