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

在 2021/6/3 下午7:34, wangyunjian 写道:

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-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Monday, May 31, 2021 11:29 AM
To: wangyunjian <redacted>; netdev@vger.kernel.org
Cc: kuba@kernel.org; davem@davemloft.net; mst@redhat.com;
virtualization@lists.linux-foundation.org; dingxiaoxiong
[off-list ref]
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:

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-----Original Message-----

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From: Yunjian Wang <redacted>

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

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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); ...

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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.

Can we introduce rx_fifo_errors for that?

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Let's leave the policy decision (link down) to userspace.

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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.

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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?

Somebody posted a prototype 3 or 4 years ago, you can search it and 
maybe we can start from there.

Thanks

Thanks

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Thanks

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Thanks

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Thanks

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