Re: 5.6-rc3: WARNING: CPU: 48 PID: 17435 at kernel/sched/fair.c:380 enqueue_task_fair+0x328/0x440

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 05/03/2020 10:30, Vincent Guittot wrote:
> Le mercredi 04 mars 2020 à 20:59:33 (+0100), Christian Borntraeger a écrit :
>>
>> On 04.03.20 20:38, Christian Borntraeger wrote:
>>>
>>> On 04.03.20 20:19, Dietmar Eggemann wrote:

[...]

> Could you try to add the patch below on top of dietmar's one so we will have the status of
> each level of the hierarchy ?
> The 1st level seems ok but something wrong happens while walking the hierarchy
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 69fc30db7440..9ccde775e02e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5331,14 +5331,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  
>         if (rq->tmp_alone_branch != &rq->leaf_cfs_rq_list) {
>                 char path[64];
> +               se = &p->se;
>  
> -               cfs_rq = cfs_rq_of(&p->se);
> +               for_each_sched_entity(se) {
> +                       cfs_rq = cfs_rq_of(se);
>  
> -               sched_trace_cfs_rq_path(cfs_rq, path, 64);
> +                       sched_trace_cfs_rq_path(cfs_rq, path, 64);
>  
> -               printk("CPU%d path=%s on_list=%d nr_running=%d p=[%s %d]\n",
> -                      cpu_of(rq), path, cfs_rq->on_list, cfs_rq->nr_running,
> +                       printk("CPU%d path=%s on_list=%d nr_running=%d throttled=%d p=[%s %d]\n",
> +                      cpu_of(rq), path, cfs_rq->on_list, cfs_rq->nr_running, cfs_rq_throttled(cfs_rq),
>                        p->comm, p->pid);
> +               }
>         }
>  
>         assert_list_leaf_cfs_rq(rq);

Yeah, that's better.

The fact that the task 'CPU 1/KVM' in
'machine-qemu\x2d16\x2dtest14.scope' hit the assert only tells us that
some list_[add|\del]_leaf_cfs_rq on CPU62 before left
rq->tmp_alone_branch != rq->leaf_cfs_rq_list.

I see that cgroup-v2 is used here.

>> [   25.680326] CPU62 path=/machine.slice/machine-test.slice/machine-qemu\x2d16\x2dtest14. on_list=1 nr_running=1 p=[CPU 1/KVM 2543]
>> [   25.680334] ------------[ cut here ]------------
>> [   25.680335] rq->tmp_alone_branch != &rq->leaf_cfs_rq_list
>> [   25.680351] WARNING: CPU: 61 PID: 2535 at kernel/sched/fair.c:380 enqueue_task_fair+0x3f6/0x4a8

[...]