On Wed, Jun 05, 2019 at 01:49:35PM +0200, Juri Lelli <juri.lelli@xxxxxxxxxx> wrote: > Existing code comes with a comment saying the "we don't support RT-tasks > being in separate groups". I'm also inclined to this check not being completely correct. This guard also prevents enabling cpu controller on unified hierarchy with !CONFIG_RT_GROUP_SCHED. (If there are any kernel RT threads in root cgroup, they can't be migrated to the newly create cpu controller's root in cgroup_update_dfl_csses().) I considered relaxing the check to non-root cgroups only, however, as your example shows, it doesn't prevent reaching the avoided state by other paths. I'm not that familiar with RT sched to tell whether RT-priority tasks in different task_groups break any assumptions. Michal
