Re: [Xen-devel] [PATCH] xen-netfront: Delete rx_refill_timer in xennet_disconnect_backend()

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/30/2017 01:07 PM, Eric Dumazet wrote:
> On Mon, 2017-01-30 at 12:45 -0500, Boris Ostrovsky wrote:
>> rx_refill_timer should be deleted as soon as we disconnect from the
>> backend since otherwise it is possible for the timer to go off before
>> we get to xennet_destroy_queues(). If this happens we may dereference
>> queue->rx.sring which is set to NULL in xennet_disconnect_backend().
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>> CC: stable@xxxxxxxxxxxxxxx
>> ---
>>  drivers/net/xen-netfront.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index 8315fe7..722fe9f 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -1379,6 +1379,8 @@ static void xennet_disconnect_backend(struct 
>> netfront_info *info)
>>      for (i = 0; i < num_queues && info->queues; ++i) {
>>              struct netfront_queue *queue = &info->queues[i];
>>  
>> +            del_timer_sync(&queue->rx_refill_timer);
>> +
> If napi_disable() was not called before this del_timer_sync(), another
> RX might come here and rearm rx_refill_timer.

We do netif_carrier_off() first thing in xennet_disconnect_backend() and
the only place where the timer is rearmed is xennet_alloc_rx_buffers(),
which is guarded by netif_carrier_ok() check.

-boris


>
>>              if (queue->tx_irq && (queue->tx_irq == queue->rx_irq))
>>                      unbind_from_irqhandler(queue->tx_irq, queue);
>>              if (queue->tx_irq && (queue->tx_irq != queue->rx_irq)) {
>> @@ -1733,7 +1735,6 @@ static void xennet_destroy_queues(struct netfront_info 
>> *info)
>>  
>>              if (netif_running(info->netdev))
>>                      napi_disable(&queue->napi);
>> -            del_timer_sync(&queue->rx_refill_timer);
>>              netif_napi_del(&queue->napi);
>>      }
>>  
>


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