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Subject: Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a
 node with 1 online CPU
From: Michael Ellerman <mpe@ellerman.id.au>
To: Tejun Heo <htejun@gmail.com>, Peter Zijlstra <peterz@infradead.org>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>,
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        Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>,
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Date: Fri, 17 Jun 2016 11:49:36 +1000
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On Thu, 2016-06-16 at 15:39 -0400, Tejun Heo wrote:
> On Thu, Jun 16, 2016 at 02:45:48PM +0200, Peter Zijlstra wrote:
> > Subject: workqueue: Fix setting affinity of unbound worker threads
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Thu Jun 16 14:38:42 CEST 2016
> > 
> > With commit e9d867a67fd03ccc ("sched: Allow per-cpu kernel threads to
> > run on online && !active"), __set_cpus_allowed_ptr() expects that only
> > strict per-cpu kernel threads can have affinity to an online CPU which
> > is not yet active.
> > 
> > This assumption is currently broken in the CPU_ONLINE notification
> > handler for the workqueues where restore_unbound_workers_cpumask()
> > calls set_cpus_allowed_ptr() when the first cpu in the unbound
> > worker's pool->attr->cpumask comes online. Since
> > set_cpus_allowed_ptr() is called with pool->attr->cpumask in which
> > only one CPU is online which is not yet active, we get the following
> > WARN_ON during an CPU online operation.
> 
> Applied to wq/for-4.7-fixes.

Thanks all.

cheers