Subject: Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a node with 1 online CPU

From: Gautham R Shenoy <[email-masked]>
Date: Fri, 15 Jul 2016 10:57:28 +0530

Hi Tejun,

On Thu, Jun 16, 2016 at 03:39:05PM -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 <[email-masked]>
> > 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.

Did this patch get missed by any chance? It is not in
the master branch of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git yet.

We're still hitting the WARN_ON() during boot-up on the mainline kernel.
> Thanks.
> -- 
> tejun

--
Thanks and Regards
gautham.