Re: [PATCH -rt 4/5] rcu: backport RCU cpu hotplug support

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Jun 10, 2008 at 01:13:03PM +0200, Peter Zijlstra wrote:
> backport the RCU cpu-hotplug support from .26-rc to .24-rt

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
>  kernel/rcupreempt.c |   58 +++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 55 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.24.7.noarch/kernel/rcupreempt.c
> ===================================================================
> --- linux-2.6.24.7.noarch.orig/kernel/rcupreempt.c
> +++ linux-2.6.24.7.noarch/kernel/rcupreempt.c
> @@ -820,6 +820,13 @@ void rcu_offline_cpu_rt(int cpu)
>  		smp_mb();  /* Subsequent RCU read-side critical sections */
>  			   /*  seen -after- acknowledgement. */
>  	}
> +
> +	__get_cpu_var(rcu_flipctr)[0] += per_cpu(rcu_flipctr, cpu)[0];
> +	__get_cpu_var(rcu_flipctr)[1] += per_cpu(rcu_flipctr, cpu)[1];
> +
> +	per_cpu(rcu_flipctr, cpu)[0] = 0;
> +	per_cpu(rcu_flipctr, cpu)[1] = 0;
> +
>  	cpu_clear(cpu, rcu_cpu_online_map);
>  	spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, oldirq);
> 
> @@ -833,8 +840,9 @@ void rcu_offline_cpu_rt(int cpu)
>  	 * fix.
>  	 */
> 
> +	local_irq_save(oldirq);
>  	rdp = RCU_DATA_ME();
> -	spin_lock_irqsave(&rdp->lock, oldirq);
> +	spin_lock(&rdp->lock);
>  	*rdp->nexttail = list;
>  	if (list)
>  		rdp->nexttail = tail;
> @@ -866,9 +874,11 @@ void rcu_process_callbacks_rt(struct sof
>  {
>  	unsigned long flags;
>  	struct rcu_head *next, *list;
> -	struct rcu_data *rdp = RCU_DATA_ME();
> +	struct rcu_data *rdp;
> 
> -	spin_lock_irqsave(&rdp->lock, flags);
> +	local_irq_save(flags);
> +	rdp = RCU_DATA_ME();
> +	spin_lock(&rdp->lock);
>  	list = rdp->donelist;
>  	if (list == NULL) {
>  		spin_unlock_irqrestore(&rdp->lock, flags);
> @@ -951,6 +961,32 @@ int rcu_pending_rt(int cpu)
>  	return 0;
>  }
> 
> +static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
> +                                unsigned long action, void *hcpu)
> +{
> +        long cpu = (long)hcpu;
> +
> +        switch (action) {
> +        case CPU_UP_PREPARE:
> +        case CPU_UP_PREPARE_FROZEN:
> +                rcu_online_cpu_rt(cpu);
> +                break;
> +        case CPU_UP_CANCELED:
> +        case CPU_UP_CANCELED_FROZEN:
> +        case CPU_DEAD:
> +        case CPU_DEAD_FROZEN:
> +                rcu_offline_cpu_rt(cpu);
> +                break;
> +        default:
> +                break;
> +        }
> +        return NOTIFY_OK;
> +}
> +
> +static struct notifier_block __cpuinitdata rcu_nb = {
> +        .notifier_call = rcu_cpu_notify,
> +};
> +
>  void __init rcu_init_rt(void)
>  {
>  	int cpu;
> @@ -972,6 +1008,22 @@ void __init rcu_init_rt(void)
>  		rdp->donetail = &rdp->donelist;
>  	}
>  	rcu_preempt_boost_init();
> +	register_cpu_notifier(&rcu_nb);
> +
> +	/*
> +         * We don't need protection against CPU-Hotplug here
> +         * since
> +         * a) If a CPU comes online while we are iterating over the
> +         *    cpu_online_map below, we would only end up making a
> +         *    duplicate call to rcu_online_cpu() which sets the corresponding
> +         *    CPU's mask in the rcu_cpu_online_map.
> +         *
> +         * b) A CPU cannot go offline at this point in time since the user
> +         *    does not have access to the sysfs interface, nor do we
> +         *    suspend the system.
> +         */
> +        for_each_online_cpu(cpu)
> +                rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
>  }
> 
>  /*
> 
> -- 
>