Re: WARN_ON_ONCE() in process_one_work()?

From	Tejun Heo <tj@kernel.org>
Newsgroups	linux.kernel
Subject	Re: WARN_ON_ONCE() in process_one_work()?
Date	2017-05-01 20:50 +0200
Message-ID	<tCoyu-4dM-17@gated-at.bofh.it> (permalink)
References	<tCmQ2-39r-27@gated-at.bofh.it> <tCooO-4aC-27@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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

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Re: WARN_ON_ONCE() in process_one_work()? Tejun Heo <tj@kernel.org> - 2017-05-01 20:50 +0200
  Re: WARN_ON_ONCE() in process_one_work()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-01 21:00 +0200
    Re: WARN_ON_ONCE() in process_one_work()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-05 19:20 +0200

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