Re: [PATCH]rcu classic: update qlen when cpu offline

[Ingo Molnar <mingo@elte.hu>]

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> On Thu, Jun 26, 2008 at 10:06:43AM +0800, Lai Jiangshan wrote:
> > 
> > When callbacks are moved from offline cpu to this cpu,
> > the qlen field of this rdp should be updated.
> 
> Good catch!!!
> 
> The effect of this bug would be for force_quiescent_state() to be invoked
> when it should not and vice versa -- wasting cycles in the first case
> and letting RCU callbacks remain piled up in the second case.  The bug
> is thus "benign" in that it does not result in premature grace-period
> termination, but should of course be fixed nonetheless.
> 
> Preemption is disabled by the caller's get_cpu_var(), so we are guaranteed
> to remain on the same CPU, as required.  The local_irq_disable() is indeed
> needed, otherwise, an interrupt might invoke call_rcu() or call_rcu_bh(),
> which could cause that interrupt's increment of ->qlen to be lost.
> 
> So this patch looks correct to me.  Good job, Jiangshan!!!
> 
> Ingo, would you be willing to add this patch to tip/core/rcu?
> 
> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

thanks, applied to tip/core/rcu. (sorry about the delay!)

	Ingo