Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected

[Peter Zijlstra]

On Fri, Jan 15, 2016 at 03:14:10PM -0800, Paul E. McKenney wrote:
> And if I make the scheduling-clock interrupt send extra wakeups to the RCU
> grace-period kthread when needed, things work even with CPU hotplug going.
> 
> The "when needed" means any time that the RCU grace-period kthread has
> been sleeping three times as long as the timeout interval.  If the first
> wakeup does nothing, it does another wakeup once per second.
> 
> So it looks like this change makes an existing problem much worse, as
> opposed to introducing a new problem.

I have a vague idea about a possible race window. Have you been
observing this on PPC or x86?

The reason I'm asking is that PPC (obviously) allows for more races :-)