linux-kernel - Re: [PATCH 6/8] PM: Add suspend blocking work.

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Date:	Wed, 28 Apr 2010 23:09:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oleg Nesterov <oleg@...hat.com>,
	Arve Hjønnevåg <arve@...roid.com>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Tejun Heo <tj@...nel.org>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 6/8] PM: Add suspend blocking work.

On Wednesday 28 April 2010, Oleg Nesterov wrote:
> On 04/27, Arve Hjønnevåg wrote:
> >
> > Allow work to be queued that will block suspend while it is pending
> > or executing. To get the same functionality in the calling code often
> > requires a separate suspend_blocker for pending and executing work, or
> > additional state and locking. This implementation does add additional
> > state and locking, but this can be removed later if we add support for
> > suspend blocking work to the core workqueue code.
> 
> I think this patch is fine.
> 
> Just one silly question,
> 
> > +int queue_suspend_blocking_work(struct workqueue_struct *wq,
> > +				struct suspend_blocking_work *work)
> > +{
> > +	int ret;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&work->lock, flags);
> > +	suspend_block(&work->suspend_blocker);
> > +	ret = queue_work(wq, &work->work);
> > +	if (ret)
> > +		work->active++;
> 
> why not
> 
> 	ret = queue_work(wq, &work->work);
> 	if (ret) {
> 		suspend_block(&work->suspend_blocker);
> 		work->active++;
> 	}
> 
> ?
> 
> Afaics, we can't race with work->func() doing unblock, we hold work-lock.
> And this way the code looks more clear.

Agreed.  Arve, any objections to doing that?

> Sorry, I had no chance to read the previous patches. After the quick look
> at 1/8 I think it is OK to call suspend_block() twice, but still...

It is.

> Or I missed something? Just curious.
> 
> 
> Hmm... actually, queue_work() can also fail if we race with cancel_ which
> temporary sets WORK_STRUCT_PENDING. In that case suspend_block() won't
> be paired by unblock ?
> 
> 
> > +int schedule_suspend_blocking_work(struct suspend_blocking_work *work)
> > +{
> > ...
> > +	ret = schedule_work(&work->work);
> 
> Off-topic. We should probably export keventd_wq to avoid the duplications
> like this.

Please see my reply to Tejun. :-)

Rafael
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