linux-kernel - Re: WARN_ON_ONCE() in process_one

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Date:   Mon, 1 May 2017 14:44:02 -0400
From:   Tejun Heo <tj@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: WARN_ON_ONCE() in process_one_work()?

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