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

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Date: Mon, 22 Jan 2024 11:14:30 +0800
From: Jason Wang <jasowang@...hat.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: Andrew Lunn <andrew@...n.ch>, Heng Qi <hengqi@...ux.alibaba.com>, 
	Paolo Abeni <pabeni@...hat.com>, Zhu Yanjun <yanjun.zhu@...el.com>, mst@...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

On Mon, Jan 22, 2024 at 10:12 AM Zhu Yanjun <yanjun.zhu@...ux.dev> wrote:
>
>
> 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.

FYI, in order to avoid a swtich of atomic or not, we need convert rx
mode setting to workqueue first:

https://www.mail-archive.com/virtualization@lists.linux-foundation.org/msg60298.html

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

Who is the "user" here, or how can the "user" know the value?

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

See another thread. The design needs to be general, or you can post a RFC.

In another thought, we've already had a tx watchdog, maybe we can have
something similar to cvq and use timeout + reset in that case.

Thans

>
> Zhu Yanjun
>
> >
> >       Andrew
>