Re: musb RPM sleep-while-atomic in 4.9-rc1

[Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Fri, Oct 21, 2016 at 02:49:05AM -0700, Tony Lindgren wrote:
> * Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> [161021 02:26]:
> > On Fri, Oct 21, 2016 at 12:08:49AM -0700, Tony Lindgren wrote:
> > > * Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> [161020 08:38]:
> > > > Hi Tony,
> > > > 
> > > > I'm getting the splat below when booting 4.9-rc1 on a BBB and
> > > > tracked it down to 65b3f50ed6fa ("usb: musb: Add PM runtime support for
> > > > MUSB DSPS glue layer") which added a synchronous RPM get in a timer
> > > > callback:
> > > 
> > > OK, sorry to hear about that. Care to email me your .config and how
> > > to reproduce and what do you have connected like a hub? Also do
> > > you use built-in gadgets or configure them via configfs?
> > 
> > It happens even with no devices connected to the host port, and with no
> > gadgets configured (or the peripheral port simply disabled). Whenever
> > the glue timer fires and calls pm_runtime_get_sync() I get the splat.
> > For some reason the might_sleep() in get_sync() does not trigger the
> > first time, which means that I see this four seconds after probe, and
> > then every other second when the timer fires.
> 
> OK. I'm totally baffled how come I did not hit this earlier with
> my tests. I did have some extra patches for using the pmic vbus irq
> for cable detection, but that's only for the peripheral instance and
> the host instance is still using timer.

Yeah, I was a bit surprised as well given that other people have also
apparently run this code. Guess CONFIG_DEBUG_ATOMIC_SLEEP must have been
disabled?

> > > > Setting the irq_safe flag seems to do the trick, but not sure that's
> > > > what you intended to do.
> > > 
> > > That's what we want to avoid as it keep the parent device permanently
> > > enabled. To avoid that we want to just queue things and deal with them
> > > from pm_runtime_resume.
> > 
> > I figured, so then that pm_runtime_get_sync() in the dsps timer callback
> > needs to go.
> 
> Agreed, that is clearly wrong to call from softirq context. I need to
> figure out what is right fix here but don't have access to my bbb
> until next week.

Ok, I'll make do with irq_safe meanwhile.

Thanks,
Johan
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