linux-kernel - Re: [Xen-devel] [PATCH] xen/events/fifo: Add missing hotplug notifier transition

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Date:	Fri, 11 Mar 2016 10:53:42 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	<linux-kernel@...r.kernel.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<rt@...utronix.de>
Subject: Re: [Xen-devel] [PATCH] xen/events/fifo: Add missing hotplug notifier
 transition

On 11/03/16 09:00, Anna-Maria Gleixner wrote:
> The evtchn_fifo_cpu_notification() hotplug callback lacks handling of
> the CPU_UP_CANCELED case. That means, if CPU_UP_PREPARE fails, the
> handle of the fifo events is not dropped.
> 
> Add handling for CPU_UP_CANCELED transition to drop the fifo events
> handle.

__evtchn_fifo_handle_events() does not releases resources, it processes
any pending events for this CPU.

This patch would only be necessary if a CPU in CPU_UP_CANCELED state may
have had unmasked interrupts.  If so you would need:


case CPU_UP_CANCELED:
          if (per_cpu(cpu_control_block, cpu))
              __evtchn_fifo_handle_events(cpu, true);
          break;

To handle the case where the control block allocation or initialization
failed during CPU_UP_PREPARE.

David

> 
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: xen-devel@...ts.xenproject.org
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> ---
>  drivers/xen/events/events_fifo.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- a/drivers/xen/events/events_fifo.c
> +++ b/drivers/xen/events/events_fifo.c
> @@ -432,6 +432,7 @@ static int evtchn_fifo_cpu_notification(
>  			ret = evtchn_fifo_alloc_control_block(cpu);
>  		break;
>  	case CPU_DEAD:
> +	case CPU_UP_CANCELED:
>  		__evtchn_fifo_handle_events(cpu, true);
>  		break;
>  	default:
> 
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>