Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stallwarnings

[Peter Zijlstra]

On Thu, 2012-09-06 at 15:22 -0700, Paul E. McKenney wrote:
> Ah!
> 
> It is perfectly legal to avoid -starting- an RCU grace period for a
> minute, or even longer.  If RCU has nothing to do, in other words, if no
> one registers any RCU callbacks, then RCU need not start a grace period.
> 
> Of course, this would mean that it would eventually be a full minute
> since the last start of a grace period.  This is not a problem, after
> all, Linux went through a full ten years before experiencing its first
> grace period.
> 
> But the stall-warning code just checked how long it had been since
> the last start of a grace period, failing to note that this grace
> period had long since completed.  So it splatted out a warning.
> This warning was spurious in the sense that there was no bug aside
> from the missing check that the grace period was still in progress.
> 
> And this commit fixes that bug in RCU. 

OK, that makes sense.. it just looks like both Steve and me got confused
by the initial changelog. 
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