[Fwd: Re: via-pmu runs device_power_down in atomic context]

[Andrew Morton]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
>
> 
> > Here, pmac has gone and unilaterally decided that device_power_down() is
> > atomic, even though device_power_down() _already_ calls suspend_device(),
> > which does down().  So I'd say you've gone and found a via-pmu bug here.
> 
> No. Look at the implementation (and the comment) in device_power_down().
> It's designed to be called with irqs off...  Of course, somebody changed
> the locking in there and it's indeed ending up calling suspend_device()
> for devices on the irq_off list which calls down ... bad bad... that's
> another bug in the drivers/power/* to add to an already long list.
> Fortunately, very few (if any) devics rely on this irq_off list. But
> sysdev's do. 

uh-huh.

> > A way of shutting up the warning would be to use an atomic notifier, but
> > it'll still be buggy.  Better would be to teach pmac_suspend_devices() not
> > to assume things which aren't true ;)
> 
> No. If we call device_power_down with interrupts enabled, very bad
> things will happen. This powermac code is very carefully crafted to do
> things in a strict order and it's along those lines that the callbacks
> in the device model were initially defined. Now, people who don't
> understand shit about how to make power management reliable may have
> broken things around, but the powermac implementation is right there.
> 

This requirement to keep interrupts off in there breaks things again and
again and again and again.  And this time: again.

It looks like we (again) have to live with it in which case conversion to
an atomic notifier is probably needed.  That may break other things though.
Alan would know.