Re: [PATCH] workqueue: fix rebind bound workers warning

[Wanpeng Li]

Hi Tejun,
2016-05-10 5:50 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>:
> Cc Thomas, the new state machine author,
> 2016-05-10 1:00 GMT+08:00 Tejun Heo <tj@xxxxxxxxxx>:
>> Hello,
>>
>> On Thu, May 05, 2016 at 09:41:31AM +0800, Wanpeng Li wrote:
>>> The boot CPU handles housekeeping duty(unbound timers, workqueues,
>>> timekeeping, ...) on behalf of full dynticks CPUs. It must remain
>>> online when nohz full is enabled. There is a priority set to every
>>> notifier_blocks:
>>>
>>> workqueue_cpu_up > tick_nohz_cpu_down > workqueue_cpu_down
>>>
>>> So tick_nohz_cpu_down callback failed when down prepare cpu 0, and
>>> notifier_blocks behind tick_nohz_cpu_down will not be called any
>>> more, which leads to workers are actually not unbound. Then hotplug
>>> state machine will fallback to undo and online cpu 0 again. Workers
>>> will be rebound unconditionally even if they are not unbound and
>>> trigger the warning in this progress.
>>
>> I'm a bit confused.  Are you saying that the hotplug statemachine may
>> invoke CPU_DOWN_FAILED w/o preceding CPU_DOWN on the same callback?
>
> I think so. CPU_DOWN_FAILED is detected in the process of CPU_DOWN_PREPARE

So any plan to apply? :-)

Regards,
Wanpeng Li