Bug was noticed via this warning:

  WARNING: CPU: 6 PID: 1 at kernel/sched/sched.h:804 detach_task_cfs_rq+0x8e8/0xb80
  rq->clock_update_flags < RQCF_ACT_SKIP
  Modules linked in:
  CPU: 6 PID: 1 Comm: systemd Not tainted 4.10.0-rc5-00140-g0874170baf55-dirty #1
  Hardware name: Supermicro SYS-4048B-TRFT/X10QBi, BIOS 1.0 04/11/2014
  Call Trace:
   dump_stack+0x4d/0x65
   __warn+0xcb/0xf0
   warn_slowpath_fmt+0x5f/0x80
   detach_task_cfs_rq+0x8e8/0xb80
   ? allocate_cgrp_cset_links+0x59/0x80
   task_change_group_fair+0x27/0x150
   sched_change_group+0x48/0xf0
   sched_move_task+0x53/0x150
   cpu_cgroup_attach+0x36/0x70
   cgroup_taskset_migrate+0x175/0x300
   cgroup_migrate+0xab/0xd0
   cgroup_attach_task+0xf0/0x190
   __cgroup_procs_write+0x1ed/0x2f0
   cgroup_procs_write+0x14/0x20
   cgroup_file_write+0x3f/0x100
   kernfs_fop_write+0x104/0x180
   __vfs_write+0x37/0x140
   vfs_write+0xb8/0x1b0
   SyS_write+0x55/0xc0
   do_syscall_64+0x61/0x170
   entry_SYSCALL64_slow_path+0x25/0x25

Reported-by: Ingo Molnar <mingo@kernel.org>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>