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

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Message-ID: <Pine.LNX.4.44L0.0906261707260.4155-100000@iolanthe.rowland.org>
Date:	Fri, 26 Jun 2009 17:13:29 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 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?  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.

> 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.

Alan Stern

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