From: Juri Lelli <juri.lelli@xxxxxxxxxx> [ Upstream commit a07db5c0865799ebed1f88be0df50c581fb65029 ] On !CONFIG_RT_GROUP_SCHED configurations it is currently not possible to move RT tasks between cgroups to which CPU controller has been attached; but it is oddly possible to first move tasks around and then make them RT (setschedule to FIFO/RR). E.g.: # mkdir /sys/fs/cgroup/cpu,cpuacct/group1 # chrt -fp 10 $$ # echo $$ > /sys/fs/cgroup/cpu,cpuacct/group1/tasks bash: echo: write error: Invalid argument # chrt -op 0 $$ # echo $$ > /sys/fs/cgroup/cpu,cpuacct/group1/tasks # chrt -fp 10 $$ # cat /sys/fs/cgroup/cpu,cpuacct/group1/tasks 2345 2598 # chrt -p 2345 pid 2345's current scheduling policy: SCHED_FIFO pid 2345's current scheduling priority: 10 Also, as Michal noted, it is currently not possible to enable 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 created CPU controller's root in cgroup_update_dfl_csses()). Existing code comes with a comment saying the "we don't support RT-tasks being in separate groups". Such comment is however stale and belongs to pre-RT_GROUP_SCHED times. Also, it doesn't make much sense for !RT_GROUP_ SCHED configurations, since checks related to RT bandwidth are not performed at all in these cases. Make moving RT tasks between CPU controller groups viable by removing special case check for RT (and DEADLINE) tasks. Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx> Reviewed-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: lizefan@xxxxxxxxxx Cc: longman@xxxxxxxxxx Cc: luca.abeni@xxxxxxxxxxxxxxx Cc: rostedt@xxxxxxxxxxx Link: https://lkml.kernel.org/r/20190719063455.27328-1-juri.lelli@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/sched/core.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ff128e281d1c6..3d24d401b9d42 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6342,10 +6342,6 @@ static int cpu_cgroup_can_attach(struct cgroup_taskset *tset) #ifdef CONFIG_RT_GROUP_SCHED if (!sched_rt_can_attach(css_tg(css), task)) return -EINVAL; -#else - /* We don't support RT-tasks being in separate groups */ - if (task->sched_class != &fair_sched_class) - return -EINVAL; #endif /* * Serialize against wake_up_new_task() such that if its -- 2.20.1
