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

From: Boris Ostrovsky
Date: Mon Jan 30 2017 - 14:33:39 EST

On 01/30/2017 02:06 PM, Eric Dumazet wrote:
> On Mon, 2017-01-30 at 13:23 -0500, Boris Ostrovsky wrote:
>> 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.
> Oh well, testing netif_carrier_ok() in packet processing fast path looks
> unusual and a waste of cpu cycles. I've never seen that pattern before.
> If one day, we remove this netif_carrier_ok() test during a cleanup,
> then the race window will open again.

I don't know much about napi but I wonder whether I can indeed disable
it in xennet_disconnect_backend(). I don't see how anything can happen
after disconnect since it unmaps the rings. And then napi is re-enabled
during reconnection in xennet_create_queues(). In which case am not sure
there is any need for xennet_destroy_queues() as everything there could
be folded into xennet_disconnect_backend().