On Thu, 17 Jan 2013, Aaron Lu wrote:
> > > @@ -515,6 +516,27 @@ void elv_bio_merged(struct request_queue *q, struct request *rq,
> > > e->type->ops.elevator_bio_merged_fn(q, rq, bio);
> > > }
> > >
> > > +#ifdef CONFIG_PM_RUNTIME
> > > +static void blk_pm_requeue_request(struct request *rq)
> > > +{
> > > + if (!(rq->cmd_flags & REQ_PM))
> > > + rq->q->nr_pending--;
> > > +}
> >
> > You don't check q->dev here. That's okay, but it means that
> > q->nr_pending will be meaningless or wrong if any I/O takes place
> > before blk_pm_runtime_init is called.
>
> Right, so I had better check q->dev here too.
>
> >
> > Therefore the kerneldoc for blk_pm_runtime_init should mention that it
> > must not be called after any requests have been submitted. Also
>
> So with the q->dev check added above, I believe this is not needed.
No, it is still needed. With the q->dev check added, q->nr_pending
will always be 0 before blk_pm_runtime_init is called. But if I/O is
taking place then the number of pending requests really isn't 0.
Either you have to make sure the q->nr_pending is always correct, even
when runtime PM isn't being used, or else the caller has to make sure
that no I/O takes place before blk_pm_runtime_init is called.
> ------------
> > mention that blk_pm_runtime_init enables runtime PM for q->dev, so the
> > caller shouldn't do it.
>
> I may misunderstandd this in last email.
>
> We didn't enable runtime PM for the device in blk_pm_runtime_init, just
> some auto suspend related settings.
Sorry, yes, you are right. In fact, the caller has to make sure that
runtime PM is enabled before calling blk_pm_runtime_init; otherwise the
autosuspend timer might not work right.
Alan Stern
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