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

Alan Stern
2009-06-27T14:51:31Z

On Sat, 27 Jun 2009, Rafael J. Wysocki wrote:

> > 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?

Come to think of it, there really is a problem here. Because the
wait_for_completion call occurs outside the spinlock, it can race with
the init_completion call. It's not good for both of them to run at the
same time; the completion's internal spinlock and list pointers could
get corrupted.

Therefore I stand by my original assertion: The struct completion
should be replaced with a wait_queue. Set the runtime_error field to
-EINPROGRESS initially, and make other threads wait until the value
changes.

Alan Stern