linux-kernel - Re: [PATCH] workqueue: fix spurious CPU locality WARN from process_one

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Date:	Sun, 22 Jul 2012 14:23:58 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, tglx@...utronix.de, linux-pm@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] workqueue: fix spurious CPU locality WARN from
 process_one_work()

On Sun, Jul 22, 2012 at 09:43:27AM -0700, Tejun Heo wrote:
> 25511a4776 "workqueue: reimplement CPU online rebinding to handle idle
> workers" added CPU locality sanity check in process_one_work().  It
> triggers if a worker is executing on a different CPU without UNBOUND
> or REBIND set.
> 
> This works for all normal workers but rescuers can trigger this
> spuriously when they're serving the unbound or a disassociated
> global_cwq - rescuers don't have either flag set and thus its
> gcwq->cpu can be a different value including %WORK_CPU_UNBOUND.
> 
> Fix it by additionally testing %GCWQ_DISASSOCIATED.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> LKML-Refence: <20120721213656.GA7783@...ux.vnet.ibm.com>
> ---
> This should fix it.  Will queue it on wq/for-3.6.

I am running my tests on it, will let you know how it goes.

							Thanx, Paul

> Thanks!
> 
>  kernel/workqueue.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1949,7 +1949,13 @@ __acquires(&gcwq->lock)
> 
>  	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
>  #endif
> +	/*
> +	 * Ensure we're on the correct CPU.  DISASSOCIATED test is
> +	 * necessary to avoid spurious warnings from rescuers servicing the
> +	 * unbound or a disassociated gcwq.
> +	 */
>  	WARN_ON_ONCE(!(worker->flags & (WORKER_UNBOUND | WORKER_REBIND)) &&
> +		     !(gcwq->flags & GCWQ_DISASSOCIATED) &&
>  		     raw_smp_processor_id() != gcwq->cpu);
> 
>  	/*
> 

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