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

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Message-ID: <1705895881.6990144-1-xuanzhuo@linux.alibaba.com>
Date: Mon, 22 Jan 2024 11:58:01 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
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,
 davem@...emloft.net,
 edumazet@...gle.com,
 kuba@...nel.org,
 virtualization@...ts.linux.dev,
 netdev@...r.kernel.org,
 Zhu Yanjun <yanjun.zhu@...ux.dev>
Subject: Re: [PATCH 1/1] virtio_net: Add timeout handler to avoid kernel hang

On Mon, 22 Jan 2024 11:14:30 +0800, Jason Wang <jasowang@...hat.com> wrote:
> 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.

But we may block by the reset ^_^ if the device is broken?

Thanks.


>
> Thans
>
> >
> > Zhu Yanjun
> >
> > >
> > >       Andrew
> >
>