3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Colin Cross <ccross@xxxxxxxxxxx> commit 454c79999f7eaedcdf4c15c449e43902980cbdf5 upstream. task_tick_rt() has an optimization to only reschedule SCHED_RR tasks if they were the only element on their rq. However, with cgroups a SCHED_RR task could be the only element on its per-cgroup rq but still be competing with other SCHED_RR tasks in its parent's cgroup. In this case, the SCHED_RR task in the child cgroup would never yield at the end of its timeslice. If the child cgroup rt_runtime_us was the same as the parent cgroup rt_runtime_us, the task in the parent cgroup would starve completely. Modify task_tick_rt() to check that the task is the only task on its rq, and that the each of the scheduling entities of its ancestors is also the only entity on its rq. Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Link: http://lkml.kernel.org/r/1337229266-15798-1-git-send-email-ccross@xxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Li Zefan <lizefan@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/rt.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1997,6 +1997,8 @@ static void watchdog(struct rq *rq, stru static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued) { + struct sched_rt_entity *rt_se = &p->rt; + update_curr_rt(rq); watchdog(rq, p); @@ -2014,12 +2016,15 @@ static void task_tick_rt(struct rq *rq, p->rt.time_slice = RR_TIMESLICE; /* - * Requeue to the end of queue if we are not the only element - * on the queue: + * Requeue to the end of queue if we (and all of our ancestors) are the + * only element on the queue */ - if (p->rt.run_list.prev != p->rt.run_list.next) { - requeue_task_rt(rq, p, 0); - set_tsk_need_resched(p); + for_each_sched_rt_entity(rt_se) { + if (rt_se->run_list.prev != rt_se->run_list.next) { + requeue_task_rt(rq, p, 0); + set_tsk_need_resched(p); + return; + } } } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html