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

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  Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected Peter Zijlstra <peterz@infradead.org> - 2016-01-29 16:30 +0100
    Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-01-31 01:30 +0100

#1321829 — Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected

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 :-)

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#1322529

On Fri, Jan 29, 2016 at 04:27:35PM +0100, Peter Zijlstra wrote:
> 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 :-)

;-)

I have been seeing this on x86.

							Thanx, Paul

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