Re: [Xen-devel] [PATCH] xen/events/fifo: Consume unprocessed events when a CPU dies

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 06/19/2015 11:15 AM, Ross Lagerwall wrote:
> When a CPU is offlined, there may be unprocessed events on a port for
> that CPU.  If the port is subsequently reused on a different CPU, it
> could be in an unexpected state with the link bit set, resulting in
> interrupts being missed. Fix this by consuming any unprocessed events
> for a particular CPU when that CPU dies.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>   drivers/xen/events/events_fifo.c | 23 ++++++++++++++++++-----
>   1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
> index 417415d..1dd0ba12 100644
> --- a/drivers/xen/events/events_fifo.c
> +++ b/drivers/xen/events/events_fifo.c
> @@ -281,7 +281,8 @@ static void handle_irq_for_port(unsigned port)
>   
>   static void consume_one_event(unsigned cpu,
>                               struct evtchn_fifo_control_block *control_block,
> -                             unsigned priority, unsigned long *ready)
> +                             unsigned priority, unsigned long *ready,
> +                             bool drop)
>   {
>         struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
>         uint32_t head;
> @@ -313,13 +314,17 @@ static void consume_one_event(unsigned cpu,
>         if (head == 0)
>                 clear_bit(priority, ready);
>   
> -	if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port))
> -               handle_irq_for_port(port);
> +       if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
> +               if (unlikely(drop))
> +                       pr_warn("Dropping pending event for port %u\n", port);
Maybe pr_info (or pr_notice)?

Also, why not do this (testing for unprocessed events) in 
xen_evtchn_close()?
-boris

> +               else
> +                       handle_irq_for_port(port);
> +       }
>   
>   	q->head[priority] = head;
>   }
>   
> -static void evtchn_fifo_handle_events(unsigned cpu)
> +static void __evtchn_fifo_handle_events(unsigned cpu, bool drop)
>   {
>         struct evtchn_fifo_control_block *control_block;
>         unsigned long ready;
> @@ -331,11 +336,16 @@ static void evtchn_fifo_handle_events(unsigned cpu)
>   
>   	while (ready) {
>                 q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
> -               consume_one_event(cpu, control_block, q, &ready);
> +               consume_one_event(cpu, control_block, q, &ready, drop);
>                 ready |= xchg(&control_block->ready, 0);
>         }
>   }
>   
> +static void evtchn_fifo_handle_events(unsigned cpu)
> +{
> +       __evtchn_fifo_handle_events(cpu, false);
> +}
> +
>   static void evtchn_fifo_resume(void)
>   {
>         unsigned cpu;
> @@ -420,6 +430,9 @@ static int evtchn_fifo_cpu_notification(struct 
> notifier_block *self,
>                 if (!per_cpu(cpu_control_block, cpu))
>                         ret = evtchn_fifo_alloc_control_block(cpu);
>                 break;
> +       case CPU_DEAD:
> +               __evtchn_fifo_handle_events(cpu, true);
> +               break;
>         default:
>                 break;
>         }

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