linux-kernel - Re: [PATCH wq/for-3.18] workqueue: apply __WQ_ORDERED to create_singlethread

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Date:	Sat, 13 Sep 2014 05:12:41 +0900
From:	Tejun Heo <theo@...hat.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org
Cc:	Gustavo Luiz Duarte <gduarte@...hat.com>,
	Mike Anderson <mike.anderson@...ibm.com>,
	Tomas Henzl <thenzl@...hat.com>
Subject: Re: [PATCH wq/for-3.18] workqueue: apply __WQ_ORDERED to
 create_singlethread_workqueue()

On Sat, Sep 13, 2014 at 04:53:28AM +0900, Tejun Heo wrote:
> From e141deffe6a30cfe7dd6ad97f21afa85b80ca3ac Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Sat, 13 Sep 2014 04:14:30 +0900
> 
> create_singlethread_workqueue() is a compat interface for singled
> threaded workqueue which maps to ordered workqueue w/ rescuer in the
> current implementation.  create_singlethread_workqueue() currently
> implemented by invoking alloc_workqueue() w/ appropriate parameters.
> 
> 8719dceae2f9 ("workqueue: reject adjusting max_active or applying
> attrs to ordered workqueues") introduced __WQ_ORDERED to protect
> ordered workqueues against dynamic attribute changes which can break
> ordering guarantees but forgot to apply it to
> create_singlethread_workqueue().  While this can be potentially
> dangerous, this isn't a problem in practice given the existing uses of
> dynamic attribute changes.
> 
> Let's make create_singlethread_workqueue() wrap
> alloc_ordered_workqueue() instead so that it inherits __WQ_ORDERED and
> can implicitly track future ordered_workqueue changes.

Oops, this is the right change but w/ wrong description and branch.
W/o __WQ_ORDERED, create_singlethread_workqueue() is broken on NUMA
setups.  Will respin the patch.

Thanks.

-- 
tejun
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