linux-kernel - Re: [PATCH 2/4] workqueues: Account unbound workqueue in a seperate list

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Date:	Sun, 30 Mar 2014 08:57:51 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Kevin Hilman <khilman@...aro.org>,
	Mike Galbraith <bitbucket@...ine.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 2/4] workqueues: Account unbound workqueue in a seperate
 list

On Thu, Mar 27, 2014 at 06:21:00PM +0100, Frederic Weisbecker wrote:
> The workqueues are all listed in a global list protected by a big mutex.
> And this big mutex is used in apply_workqueue_attrs() as well.
> 
> Now as we plan to implement a directory to control the cpumask of
> all non-ABI unbound workqueues, we want to be able to iterate over all
> unbound workqueues and call apply_workqueue_attrs() for each of
> them with the new cpumask.
> 
> But the risk for a deadlock is on the way: we need to iterate the list
> of workqueues under wq_pool_mutex. But then apply_workqueue_attrs()
> itself calls wq_pool_mutex.

Wouldn't the right thing to do would be factoring out
apply_workqueue_attrs_locked()?  It's cleaner to block out addition of
new workqueues while the masks are being updated anyway.

Thanks.

-- 
tejun
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