linux-kernel - Re: Stack trace when removing Thunderbolt devices while kernel shutting down

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Message-ID: <PSXP216MB043813ED0773A4D7E842B3A680110@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
Date:   Tue, 18 Feb 2020 16:57:29 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     Lukas Wunner <lukas@...ner.de>
CC:     Bjorn Helgaas <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: Stack trace when removing Thunderbolt devices while kernel
 shutting down

On Tue, Feb 18, 2020 at 04:01:24PM +0100, Lukas Wunner wrote:
> On Tue, Feb 18, 2020 at 02:18:40PM +0000, Nicholas Johnson wrote:
> > If I surprise remove Thunderbolt 3 devices just as the kernel is 
> > shutting down, I get stack dumps, when those devices would not normally 
> > cause stack dumps if the kernel were not shutting down.
> > 
> > Because the kernel is shutting down, it makes it difficult to capture 
> > the logs without a serial console.
> 
> Hold a camera in front of the screen and try to capture the messages
> as an MP4 movie which can be uploaded to YouTube or something.
https://www.youtube.com/watch?v=sDcYmbz7GME

The above is unlisted and will not appear in any search, so it will not 
confuse my subscribers, but anybody with the link can view it (public).

I am still not sure I like the sound of my own voice. *cringe*

> 
> If the output moves too fast to capture it, artificially slow it down
> by adding a udelay() to call_console_drivers() in kernel/printk/printk.c.

If you cannot get anything useful out of the aforementioned video, then 
I will do this tomorrow evening. It is almost 1am now.

> 
> Thanks,
> 
> Lukas

By the way, this is not just with Linux v5.6-rcX. I have noticed this 
for some time but it has been lower down my list in terms of priority 
and urgency. I half expected it to be of no interest. I should have 
mentioned it earlier, but before I might not have had as much time to 
help investigate. I am currently looking for new kernel development 
tasks because my previous ones are done.

Thanks,
Nicholas