linux-kernel - Re: [PATCH] xen: xen-pciback: Remove create

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Date:	Fri, 27 May 2016 12:08:22 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	jgross@...e.com, JBeulich@...e.com, paul.gortmaker@...driver.com,
	stefano.stabellini@...citrix.com, cardoe@...doe.com,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: xen-pciback: Remove create_workqueue

Hello,

On Fri, May 27, 2016 at 12:01:14PM -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, May 27, 2016 at 09:24:11PM +0530, Bhaktipriya Shridhar wrote:
> > With concurrency managed workqueues, use of dedicated workqueues can be
> > replaced by using system_wq. Drop host->intr_wq by using
                                      ^
				      xen_pcibk_wq
> > system_wq.
> > 
> > Since there is only a single work item, increase of concurrency level by
> > switching to system_wq should not break anything.
> 
> _should_ not? Hehe. I presume this has not been tested?

Yeah, this is a part of sweeping conversions and it's challenging (and
often impossible for specific drivers) to setup test environments.
xen isn't as bad but can still be a pretty specialized setup.  The
conversions aren't high risk and shouldn't be too difficult to root
cause when something goes south.  We'd greatly appreciate any helps
with reviewing and testing.

> > cancel_work_sync() has been used in xen_pcibk_disconnect() to ensure that
> > work item is not pending or executing by the time exit path runs.
> > 
> > Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
> > @@ -76,8 +75,7 @@ static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev)
> >  	/* If the driver domain started an op, make sure we complete it
> >  	 * before releasing the shared memory */
> > 
> > -	/* Note, the workqueue does not use spinlocks at all.*/
> > -	flush_workqueue(xen_pcibk_wq);
> > +	cancel_work_sync(&pdev->op_work);

Should it be flush_work() instead?  Is it okay for a pdev->op_work to
be queued and canceled without actually getting executed?

Thanks.

-- 
tejun