netdev - Re: [RFC net-next] net: don't dump stack on queue timeout

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Date: Fri, 10 Nov 2023 11:21:37 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Daniele Palmas <dnlplm@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, syzbot+d55372214aff0faa1f1f@...kaller.appspotmail.com,
 jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us
Subject: Re: [RFC net-next] net: don't dump stack on queue timeout

On Fri, 10 Nov 2023 09:01:29 +0100 Daniele Palmas wrote:
> The problem is that the MBIM standard does not define the
> CDC_NOTIFY_NETWORK_CONNECTION, so carrier loss detection is managed
> through the indications on the control channel.
> 
> But the kernel is not aware of what's passing through the control
> channel, so it's the userspace tool that should detect carrier loss,
> disconnect the bearers and set the network interface down.
> 
> For example, ModemManager is capable of doing that, but the problem is
> that usually the standard modem notifications on the control channel
> arrive later than the splat: increasing watchdog_timeo does not seem
> to me a good option, since the notification could arrive much later.
> 
> One possible solution is to have some proprietary notifications on the
> control channel that detect RLF early and trigger the above described
> process before the warn happens: by coincidence, I wrote a custom
> ModemManager patch for this a few days ago
> https://gitlab.freedesktop.org/dnlplm/ModemManager/-/commit/89ba8ab65d4bfbd4cf1ff11ed58c08b112aca80f

I see, thanks for the extra info!