[tip:sched/core] sched/core: Add debugging code to catch missing update_rq_clock() calls

[Mike Galbraith]

On Fri, 2017-02-03 at 09:53 +0100, Peter Zijlstra wrote:
> On Fri, Feb 03, 2017 at 10:03:14AM +0530, Sachin Sant wrote:

> > I ran few cycles of cpu hot(un)plug tests. In most cases it works except one
> > where I ran into rcu stall:
> > 
> > [  173.493453] INFO: rcu_sched detected stalls on CPUs/tasks:
> > [  173.493473] > > 	> > 8-...: (2 GPs behind) idle=006/140000000000000/0 softirq=0/0 fqs=2996 
> > [  173.493476] > > 	> > (detected by 0, t=6002 jiffies, g=885, c=884, q=6350)
> 
> Right, I actually saw that too, but I don't think that would be related
> to my patch. I'll see if I can dig into this though, ought to get fixed
> regardless.

FWIW, I'm not seeing stalls/hangs while beating hotplug up in tip. (so
next grew a wart?)

	-Mike