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

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Message-Id: <20160715052728.GA5072@in.ibm.com>
Date:	Fri, 15 Jul 2016 10:57:28 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a
 node with 1 online CPU

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 <peterz@...radead.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.

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.