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

[Alan Stern]

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/