Subject: Re: [Xen-devel] [PATCH net v2 1/3] xen-netback: move NAPI add/remove calls

From: David Vrabel <[email-masked]>
Date: Mon, 11 Aug 2014 14:01:06 +0100

On 11/08/14 13:49, Zoltan Kiss wrote:
> On 11/08/14 13:35, David Vrabel wrote:
>> On 08/08/14 17:37, Wei Liu wrote:
>>> Originally napi_add was in init_queue and napi_del was in deinit_queue,
>>> while kthreads were handled in _connect and _disconnect. Move napi_add
>>> and napi_remove to _connect and _disconnect so that they reside togother
>>> with kthread operations.
>>>
>>> Signed-off-by: Wei Liu <[email-masked]>
>>> Cc: Ian Campbell <[email-masked]>
>>> Cc: Zoltan Kiss <[email-masked]>
>>> ---
>>>   drivers/net/xen-netback/interface.c |   12 ++++++++----
>>>   1 file changed, 8 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/net/xen-netback/interface.c
>>> b/drivers/net/xen-netback/interface.c
>>> index 48a55cd..fdb4fca 100644
>>> --- a/drivers/net/xen-netback/interface.c
>>> +++ b/drivers/net/xen-netback/interface.c
>>> @@ -528,9 +528,6 @@ int xenvif_init_queue(struct xenvif_queue *queue)
>>>
>>>       init_timer(&queue->rx_stalled);
>>>
>>> -    netif_napi_add(queue->vif->dev, &queue->napi, xenvif_poll,
>>> -            XENVIF_NAPI_WEIGHT);
>>> -
>>>       return 0;
>>>   }
>>>
>>> @@ -618,6 +615,9 @@ int xenvif_connect(struct xenvif_queue *queue,
>>> unsigned long tx_ring_ref,
>>>       wake_up_process(queue->task);
>>>       wake_up_process(queue->dealloc_task);
>>>
>>> +    netif_napi_add(queue->vif->dev, &queue->napi, xenvif_poll,
>>> +            XENVIF_NAPI_WEIGHT);
>>> +
>>>       return 0;
>>>
>>>   err_rx_unbind:
>>> @@ -675,6 +675,11 @@ void xenvif_disconnect(struct xenvif *vif)
>>>
>>>       for (queue_index = 0; queue_index < num_queues; ++queue_index) {
>>>           queue = &vif->queues[queue_index];
>>> +        netif_napi_del(&queue->napi);
>>> +    }
>>
>> Why have you added an additional loop over all the queues?  The ordering
>> looks wrong as well.  I think you want
>>
>>    1. unbind from irqhandler
>>    2. napi del
>>    3. stop task
>>    4. stop dealloc task
>>    5. unmap frontend rings.
> And that's how they are ordered.

No, it isn't.  Did you mistakenly look at netfront which is correctly
ordered already?

You must unbind the irq handler before calling netif_napi_del() or an
interrupt may occur and the handler may call napi_schedule() with a
deleted instance.

David