sched/rt: Fix rq->clock_update_flags < RQCF_ACT_SKIP warning

While running rt-tests' pi_stress program I got the following splat:

  rq->clock_update_flags < RQCF_ACT_SKIP
  WARNING: CPU: 27 PID: 0 at kernel/sched/sched.h:960 assert_clock_updated.isra.38.part.39+0x13/0x20

  [...]

  <IRQ>
  enqueue_top_rt_rq+0xf4/0x150
  ? cpufreq_dbs_governor_start+0x170/0x170
  sched_rt_rq_enqueue+0x65/0x80
  sched_rt_period_timer+0x156/0x360
  ? sched_rt_rq_enqueue+0x80/0x80
  __hrtimer_run_queues+0xfa/0x260
  hrtimer_interrupt+0xcb/0x220
  smp_apic_timer_interrupt+0x62/0x120
  apic_timer_interrupt+0xf/0x20
  </IRQ>

  [...]

  do_idle+0x183/0x1e0
  cpu_startup_entry+0x5f/0x70
  start_secondary+0x192/0x1d0
  secondary_startup_64+0xa5/0xb0

We can get rid of it be the "traditional" means of adding an
update_rq_clock() call after acquiring the rq->lock in
do_sched_rt_period_timer().

The case for the RT task throttling (which this workload also hits)
can be ignored in that the skip_update call is actually bogus and
quite the contrary (the request bits are removed/reverted).

By setting RQCF_UPDATED we really don't care if the skip is happening
or not and will therefore make the assert_clock_updated() check happy.

Signed-off-by: Davidlohr Bueso <[email protected]>
Reviewed-by: Matt Fleming <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: Davidlohr Bueso

kernel/sched/rt.c

@@ -839,6 +839,8 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
 			continue;
 
 		raw_spin_lock(&rq->lock);
+		update_rq_clock(rq);
+
 		if (rt_rq->rt_time) {
 			u64 runtime;