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

Rafael J. Wysocki
2010-04-28T21:09:42Z

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