Commit 52d15521 authored by Yicong Yang's avatar Yicong Yang Committed by Peter Zijlstra
Browse files

sched/deadline: Don't count nr_running for dl_server proxy tasks 



On CPU offline the kernel stalled with below call trace:

  INFO: task kworker/0:1:11 blocked for more than 120 seconds.

cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd.
This is because we count nr_running twice on cpuhp enqueuing and failed
the wait condition of cpuhp:

  enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0
    dl_server_start()
      [...]
      add_nr_running() // rq->nr_running = 1
    add_nr_running() // rq->nr_running = 2
  [switch to cpuhp, waiting on balance_hotplug_wait()]
  rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2
    schedule() // wait again

It doesn't make sense to count the dl_server towards runnable tasks,
since it runs other tasks.

Fixes: 63ba8422 ("sched/deadline: Introduce deadline servers")
Signed-off-by: default avatarYicong Yang <yangyicong@hisilicon.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250627035420.37712-1-yangyicong@huawei.com
parent 421fc59c

kernel/sched/deadline.c

+6 −2
Original line number Diff line number Diff line
@@ -1851,6 +1851,8 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq) 
	u64 deadline = dl_se->deadline;



	dl_rq->dl_nr_running++;



	if (!dl_server(dl_se))

		add_nr_running(rq_of_dl_rq(dl_rq), 1);



	inc_dl_deadline(dl_rq, deadline);
@@ -1861,6 +1863,8 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq) 
{

	WARN_ON(!dl_rq->dl_nr_running);

	dl_rq->dl_nr_running--;



	if (!dl_server(dl_se))

		sub_nr_running(rq_of_dl_rq(dl_rq), 1);



	dec_dl_deadline(dl_rq, dl_se->deadline);