netdev - Re: [PATCH] xen-netfront: Delete rx_refill_timer in xennet_disconnect

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Message-ID: <07a315d6-7c97-6d11-fa18-548000107c2f@oracle.com>
Date:   Mon, 30 Jan 2017 14:31:58 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     jgross@...e.com, xen-devel@...ts.xenproject.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        vineethp@...zon.com, wei.liu2@...rix.com, paul.durrant@...rix.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] xen-netfront: Delete rx_refill_timer in
 xennet_disconnect_backend()

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().

-boris