On 6/21/21 5:25 PM, Steven Rostedt wrote:

On Mon, 21 Jun 2021 13:34:44 +0200
Daniel Bristot de Oliveira [off-list ref] wrote:

quoted

quoted

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.

quoted

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