Re: [PATCH V4 05/12] trace/hwlat: Support hotplug operations

[Daniel Bristot de Oliveira]

On 6/21/21 5:25 PM, Steven Rostedt wrote:
> On Mon, 21 Jun 2021 13:34:44 +0200
> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
> 
>>> And of course, because get_online_cpus() is called within
>>> trace_types_lock, doing this check is going to cause a lock inversion.
>>>  
>> Yep! I tried to take the trace_type_lock here, and got the lockdep info about
>> this problem.
>>
>>> The only thing I could think of is to wake up a worker thread to do the
>>> work. That is, this just wakes the worker thread, then the worker grabs
>>> the trace_types_lock, iterates through the cpu mask of expect running
>>> threads, and then starts or kills them depending on the hwlat_busy
>>> value.  
>> So, it will not wait for the kworker to run?
> What wont wait?

For example, at the shutdown, should the hotplug callback wait for the workqueue
to run & kill the thread, or not?

-- Daniel

> -- Steve
>