linux-kernel - Re: [patch update] PM: Introduce core framework for run-time PM of I/O devices (rev. 6)

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Date:	Sat, 27 Jun 2009 00:32:44 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [patch update] PM: Introduce core framework for run-time PM of I/O devices (rev. 6)

On Friday 26 June 2009, Alan Stern wrote:
> On Fri, 26 Jun 2009, Rafael J. Wysocki wrote:
> 
> > > It occurs to me that the problem would be solved if were a cancel_work
> > > routine.  In the same vein, it ought to be possible for
> > > cancel_delayed_work to run in interrupt context.  I'll see what can be
> > > done.
> > 
> > Having looked at the workqueue code I'm not sure if there's a way to implement
> > that in a non-racy way.  Which may be the reason why there are no such
> > functions already. :-)
> 
> Well, I'll give it a try.
> 
> Speaking of races, have you noticed that the way power.work_done gets 
> used is racy?

Not really. :-)

> You can't wait for the completion before releasing the 
> lock, but then anything could happen.
> 
> A safer approach would be to use a wait_queue.

I'm not sure what you mean exactly.  What's the race?

> > In the meantime I reworked the patch (below) to use more RPM_* flags and I
> > removed the runtime_break and runtime_notify bits from it.  Also added some
> > comments to explain some non-obvious steps (hope that helps).
> > 
> > I also added the pm_runtime_put_atomic() and pm_runtime_put() as per the
> > comment above.
> > 
> > It seems to be a bit cleaner this way, but that's my personal view. :-)
> 
> I'll look at it over the weekend.  And I'll try to see if proper 
> cancel_work and cancel_delayed_work functions can help clean it up.

Great, thanks!

Best,
Rafael
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