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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 19/06/15 17:02, Boris Ostrovsky wrote:
> 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)?

We want a warning here because we think this shouldn't happen -- if it
does we actually need to retrigger the event on its new CPU.

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

We can't do anything about them when closing because they may be in the
middle of a queue.

David

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