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

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Message-ID: <20140403144826.GE23338@localhost.localdomain>
Date:	Thu, 3 Apr 2014 16:48:28 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
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 Sun, Mar 30, 2014 at 08:57:51AM -0400, Tejun Heo wrote:
> 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.

I'm not quite sure I get what you suggest. Do you mean have apply_workqueue_attrs_locked()
calling apply_workqueue_attrs() under the lock on this patch?

Thanks.
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