sched/fair: Use rq_lock/unlock in online_fair_sched_group

sched/fair: Use rq_lock/unlock in online_fair_sched_group

Enabling WARN_DOUBLE_CLOCK in /sys/kernel/debug/sched_features causes
warning to fire in update_rq_clock. This seems to be caused by onlining
a new fair sched group not using the rq lock wrappers.

  [] rq->clock_update_flags & RQCF_UPDATED
  [] WARNING: CPU: 5 PID: 54385 at kernel/sched/core.c:210 update_rq_clock+0xec/0x150

  [] Call Trace:
  []  online_fair_sched_group+0x53/0x100
  []  cpu_cgroup_css_online+0x16/0x20
  []  online_css+0x1c/0x60
  []  cgroup_apply_control_enable+0x231/0x3b0
  []  cgroup_mkdir+0x41b/0x530
  []  kernfs_iop_mkdir+0x61/0xa0
  []  vfs_mkdir+0x108/0x1a0
  []  do_mkdirat+0x77/0xe0
  []  do_syscall_64+0x55/0x1d0
  []  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Using the wrappers in online_fair_sched_group instead of the raw locking
removes this warning.

[ tglx: Use rq_*lock_irq() ]

Signed-off-by: Phil Auld <pauld@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20190801133749.11033-1-pauld@redhat.com