linux-kernel - Re: [PATCH] virtio_net: Remove BUG() to aviod machine dead

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Date:   Wed, 2 Jun 2021 15:14:50 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Xianting Tian <xianting.tian@...ux.alibaba.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, davem@...emloft.net,
        kuba@...nel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_net: Remove BUG() to aviod machine dead


在 2021/6/2 下午1:59, Leon Romanovsky 写道:
> On Tue, May 25, 2021 at 02:19:03PM +0800, Jason Wang wrote:
>> 在 2021/5/19 下午10:18, Xianting Tian 写道:
>>> thanks, I submit the patch as commented by Andrew
>>> https://lkml.org/lkml/2021/5/18/256
>>>
>>> Actually, if xmit_skb() returns error, below code will give a warning
>>> with error code.
>>>
>>>      /* Try to transmit */
>>>      err = xmit_skb(sq, skb);
>>>
>>>      /* 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;
>>>      }
>>>
>>>
>>>
>>>
>>>
>>> 在 2021/5/18 下午5:54, Michael S. Tsirkin 写道:
>>>> typo in subject
>>>>
>>>> On Tue, May 18, 2021 at 05:46:56PM +0800, Xianting Tian wrote:
>>>>> When met error, we output a print to avoid a BUG().
>>
>> So you don't explain why you need to remove BUG(). I think it deserve a
>> BUG().
> BUG() will crash the machine and virtio_net is not kernel core
> functionality that must stop the machine to prevent anything truly
> harmful and basic.


Note that the BUG() here is not for virtio-net itself. It tells us that 
a bug was found by virtio-net.

That is, the one that produces the skb has a bug, usually it's the 
network core.

There could also be the issue of the packet from untrusted source 
(userspace like TAP or packet socket) but they should be validated there.

Thanks


>
> I would argue that code in drivers/* shouldn't call BUG() macros at all.
>
> If it is impossible, don't check for that or add WARN_ON() and recover,
> but don't crash whole system.
>
> Thanks
>