linux-kernel - Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state machine

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Date:	Mon, 15 Aug 2016 16:06:25 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<david.vrabel@...rix.com>, <jgross@...e.com>
CC:	<xen-devel@...ts.xenproject.org>, <bigeasy@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state
 machine

On 15/08/16 15:46, Boris Ostrovsky wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> Install the callbacks via the state machine.
[...]
> +static int xen_evtchn_cpu_dead(unsigned int cpu)
> +{
> +	__evtchn_fifo_handle_events(cpu, true);
> +	return 0;
> +}

I'm not familiar with the new state machine.  When this is called, what
state is the CPU in?

In particular, local interrupts must be disabled and all non-percpu irqs
must have been migrated to other CPUs.


>  int __init xen_evtchn_fifo_init(void)
>  {
> @@ -456,7 +444,9 @@ int __init xen_evtchn_fifo_init(void)
>  
>  	evtchn_ops = &evtchn_ops_fifo;
>  
> -	register_cpu_notifier(&evtchn_fifo_cpu_notifier);
> +	cpuhp_setup_state_nocalls(CPUHP_XEN_EVTCHN_PREPARE,
> +				  "CPUHP_XEN_EVTCHN_PREPARE",
> +				  xen_evtchn_cpu_prepare, xen_evtchn_cpu_dead);
>  out:
>  	put_cpu();
>  	return ret;
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index d6beeb9..c60a17c 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -22,6 +22,7 @@ enum cpuhp_state {
>  	CPUHP_SMPCFD_PREPARE,
>  	CPUHP_RCUTREE_PREP,
>  	CPUHP_XEN_PREPARE,
> +	CPUHP_XEN_EVTCHN_PREPARE,
>  	CPUHP_NOTIFY_PREPARE,
>  	CPUHP_TIMERS_DEAD,
>  	CPUHP_BRINGUP_CPU,
>