netdev - Re: [PATCH 1/1] virtio_net: Add timeout handler to avoid kernel hang

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Message-ID: <64270652-8e0c-4db7-b245-b970d9588918@linux.dev>
Date: Mon, 22 Jan 2024 10:12:15 +0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: Andrew Lunn <andrew@...n.ch>, Heng Qi <hengqi@...ux.alibaba.com>
Cc: Paolo Abeni <pabeni@...hat.com>, Zhu Yanjun <yanjun.zhu@...el.com>,
 mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 virtualization@...ts.linux.dev, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] virtio_net: Add timeout handler to avoid kernel hang


在 2024/1/20 1:29, Andrew Lunn 写道:
>>>>>        while (!virtqueue_get_buf(vi->cvq, &tmp) &&
>>>>> -           !virtqueue_is_broken(vi->cvq))
>>>>> +           !virtqueue_is_broken(vi->cvq)) {
>>>>> +        if (timeout)
>>>>> +            timeout--;
>>>> This is not really a timeout, just a loop counter. 200 iterations could
>>>> be a very short time on reasonable H/W. I guess this avoid the soft
>>>> lockup, but possibly (likely?) breaks the functionality when we need to
>>>> loop for some non negligible time.
>>>>
>>>> I fear we need a more complex solution, as mentioned by Micheal in the
>>>> thread you quoted.
>>> Got it. I also look forward to the more complex solution to this problem.
>> Can we add a device capability (new feature bit) such as ctrq_wait_timeout
>> to get a reasonable timeout？
> The usual solution to this is include/linux/iopoll.h. If you can sleep
> read_poll_timeout() otherwise read_poll_timeout_atomic().

I read carefully the functions read_poll_timeout() and 
read_poll_timeout_atomic(). The timeout is set by the caller of the 2 
functions.

As such, can we add a module parameter to customize this timeout value 
by the user?

Or this timeout value is stored in device register, virtio_net driver 
will read this timeout value at initialization?

Zhu Yanjun

>
> 	Andrew