netdev - Re: [PATCH v2] virtio_net: avoid using netif_tx

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Date:   Wed, 17 Oct 2018 17:02:35 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Ake Koomsin <ake@...l.co.jp>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] virtio_net: avoid using netif_tx_disable() for
 serializing tx routine


On 2018/10/17 下午3:59, Ake Koomsin wrote:
> Commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
> introduces netif_tx_disable() after netif_device_detach() in order to
> avoid use-after-free of tx queues. However, there are two issues.
>
> 1) Its operation is redundant with netif_device_detach() if the interface
>     is running.
> 2) In case of the interface is not running before suspending and
>     resuming, the tx does not get resumed by netif_device_attach().
>     This results in losing network connectivity.
>
> It is better to use netif_tx_lock()/netif_tx_unlock() instead for
> serializing tx routine during reset. This also preserves the symmetry
> of netif_device_detach() and netif_device_attach().
>
> Fixes commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
> Signed-off-by: Ake Koomsin <ake@...l.co.jp>
> ---
>   drivers/net/virtio_net.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 3f5aa59c37b7..41ccf9c994a4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2267,8 +2267,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
>   	/* Make sure no work handler is accessing the device */
>   	flush_work(&vi->config_work);
>   
> +	netif_tx_lock(vi->dev);
>   	netif_device_detach(vi->dev);
> -	netif_tx_disable(vi->dev);
> +	netif_tx_unlock(vi->dev);


Sorry for not finding this earlier. I think we should use 
netif_tx_lock_bh() to prevent start_xmit() to run under bh.

Thanks


>   	cancel_delayed_work_sync(&vi->refill);
>   
>   	if (netif_running(vi->dev)) {
> @@ -2304,7 +2305,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>   		}
>   	}
>   
> +	netif_tx_lock(vi->dev);
>   	netif_device_attach(vi->dev);
> +	netif_tx_unlock(vi->dev);
>   	return err;
>   }
>