Re: [bisected] "sched: Allow per-cpu kernel threads to run on online && !active" causes warning

[Ming Lei <tom.leiming@gmail.com>]

On Sat, Jul 30, 2016 at 7:25 PM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> On Wed, Jul 27, 2016 at 05:23:05PM +0200, Thomas Gleixner wrote:
>> On Wed, 27 Jul 2016, Heiko Carstens wrote:
>> > [    3.162961] ([<0000000000176c30>] select_task_rq+0xc0/0x1a8)
>> > [    3.162963] ([<0000000000177d64>] try_to_wake_up+0x2e4/0x478)
>> > [    3.162968] ([<000000000015d46c>] create_worker+0x174/0x1c0)
>> > [    3.162971] ([<0000000000161a98>] alloc_unbound_pwq+0x360/0x438)
>>
>> > For some unknown reason select_task_rq() gets called with a task that has
>> > nr_cpus_allowed == 0. Hence "cpu = cpumask_any(tsk_cpus_allowed(p));"
>> > within select_task_rq() will set cpu to nr_cpu_ids which in turn causes the
>> > warning later on.
>> >
>> > It only happens with more than one node, otherwise it seems to work fine.
>> >
>> > Any idea what could be wrong here?
>>
>> create_worker()
>>     tsk = kthread_create_on_node();
>>     kthread_bind_mask(tsk, pool->attrs->cpumask);
>>         do_set_cpus_allowed(tsk, mask);
>>             set_cpus_allowed_common(tsk, mask);
>>                 cpumask_copy(&tsk->cpus_allowed, mask);
>>                 tsk->nr_cpus_allowed = cpumask_weight(mask);
>>     wake_up_process(task);
>>
>> So this looks like pool->attrs->cpumask is simply empty.....
>
> Just had some time to look into this a bit more. Looks like we initialize
> the cpu_to_node_masks (way) too late on s390 for fake numa. So Peter's
> patch just revealed that problem.
>
> I'll see if initializing the masks earlier will fix this, but I think it
> will.

Hello,

Is there any fix for this issue?  I can see the issue on arm64 running
v4.7 kernel too.  And the oops can be avoided by reverting commit
e9d867a(sched: Allow per-cpu kernel threads to run on online && !active).


Thanks,
Ming Lei