netdev - RE: [PATCH net-next] virtio_net: set link state down when virtqueue is broken

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Date:   Thu, 3 Jun 2021 11:34:47 +0000
From:   wangyunjian <wangyunjian@...wei.com>
To:     Jason Wang <jasowang@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "mst@...hat.com" <mst@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        dingxiaoxiong <dingxiaoxiong@...wei.com>
Subject: RE: [PATCH net-next] virtio_net: set link state down when virtqueue
 is broken

> -----Original Message-----
> From: Jason Wang [mailto:jasowang@...hat.com]
> Sent: Monday, May 31, 2021 11:29 AM
> To: wangyunjian <wangyunjian@...wei.com>; netdev@...r.kernel.org
> Cc: kuba@...nel.org; davem@...emloft.net; mst@...hat.com;
> virtualization@...ts.linux-foundation.org; dingxiaoxiong
> <dingxiaoxiong@...wei.com>
> Subject: Re: [PATCH net-next] virtio_net: set link state down when virtqueue is
> broken
> 
> 
> 在 2021/5/28 下午6:58, wangyunjian 写道:
> >> -----Original Message-----
> >>> From: Yunjian Wang <wangyunjian@...wei.com>
> >>>
> >>> The NIC can't receive/send packets if a rx/tx virtqueue is broken.
> >>> However, the link state of the NIC is still normal. As a result, the
> >>> user cannot detect the NIC exception.
> >>
> >> Doesn't we have:
> >>
> >>          /* This should not happen! */
> >>           if (unlikely(err)) {
> >>                   dev->stats.tx_fifo_errors++;
> >>                   if (net_ratelimit())
> >>                           dev_warn(&dev->dev,
> >>                                    "Unexpected TXQ (%d)
> queue
> >> failure: %d\n",
> >>                                    qnum, err);
> >>                   dev->stats.tx_dropped++;
> >>                   dev_kfree_skb_any(skb);
> >>                   return NETDEV_TX_OK;
> >>           }
> >>
> >> Which should be sufficient?
> > There may be other reasons for this error, e.g -ENOSPC(no free desc).
> 
> 
> This should not happen unless the device or driver is buggy. We always reserved
> sufficient slots:
> 
>          if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
>                  netif_stop_subqueue(dev, qnum); ...
> 
> 
> > And if rx virtqueue is broken, there is no error statistics.
> 
> 
> Feel free to add one if it's necessary.

Currently receiving scenario, it is impossible to distinguish whether the reason for
not receiving packet is virtqueue's broken or no packet.

> 
> Let's leave the policy decision (link down) to userspace.
> 
> 
> >
> >>
> >>> The driver can set the link state down when the virtqueue is broken.
> >>> If the state is down, the user can switch over to another NIC.
> >>
> >> Note that, we probably need the watchdog for virtio-net in order to
> >> be a complete solution.
> > Yes, I can think of is that the virtqueue's broken exception is detected on
> watchdog.
> > Is there anything else that needs to be done?
> 
> 
> Basically, it's all about TX stall which watchdog tries to catch. Broken vq is only
> one of the possible reason.

Are there any plans for the watchdog?

Thanks

> 
> Thanks
> 
> 
> >
> > Thanks
> >
> >> Thanks
> >>
> >>