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

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Date:	Mon, 11 Aug 2014 14:14:16 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>, <netdev@...r.kernel.org>,
	<xen-devel@...ts.xen.org>
CC:	Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCH net v2 1/3] xen-netback: move NAPI add/remove
 calls

On 11/08/14 14:01, David Vrabel wrote:
> 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 <wei.liu2@...rix.com>
>>>> Cc: Ian Campbell <ian.campbell@...rix.com>
>>>> Cc: Zoltan Kiss <zoltan.kiss@...rix.com>
>>>> ---
>>>>    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.
I think xenvif_carrier_off (which call xenvif_down) does that. It is 
right before this new napi_del in xenvif_disconnect.

Zoli
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