Re: WARN_ON_ONCE() in process_one_work()?

[Tejun Heo]

Hello, Paul.

On Mon, May 01, 2017 at 11:38:07AM -0700, Paul E. McKenney wrote:
> On Mon, May 01, 2017 at 09:57:47AM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > I am hitting this WARN_ON_ONCE() in process_one_work() and am wondering
> > what I did wrong to make this happen:
> 
> Oh, wait...  Rescuer, it says.  Might this be due to the fact that RCU's
> expedited grace periods block within a workqueue handler?  Might this
> in turn run the system out of workqueue kthreads?  If this is the likely
> cause, my approach would be to rework the expected-grace-period workqueue
> handler to return when waiting for the grace period to complete, and to
> replace the current wakeup with a schedule_work() or something similar.

That should be completely fine.  It could just be that the rescuer
path has a bug around CPU hotplug handling.  Can you please confirm
either way on the cpuset usage?

Thanks.

-- 
tejun