linux-kernel - Re: kernel crash/disc errors when unbinding USB devices

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Date:   Sun, 23 Jan 2022 12:59:21 +0100
From:   Helge Deller <deller@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org,
        Linux Kernel Development <linux-kernel@...r.kernel.org>
Subject: Re: kernel crash/disc errors when unbinding USB devices

On 1/23/22 12:07, Greg Kroah-Hartman wrote:
> On Sun, Jan 23, 2022 at 11:40:01AM +0100, Helge Deller wrote:
>> On all kernels 5.15.x and 5.16.x I noticed that resetting
>> the USB devices with this shell script:
>>
>>        for i in $(ls /sys/bus/pci/drivers/ahci/|grep :)
>>          do
>>          echo $i
>>          echo $i >/sys/bus/pci/drivers/ahci/unbind
>>          sleep 1
>>          echo $i >/sys/bus/pci/drivers/ahci/bind
>>         done
>
> That is dangerous to do, why do this?  All of your block devices might
> have disappeard.
>
>>         # reseting USB3 ports (if there none you'll get errors)
>>         for i in $(ls /sys/bus/pci/drivers/xhci_hcd/|grep :)
>>          do
>>          echo $i
>>          echo $i >/sys/bus/pci/drivers/xhci_hcd/unbind
>>          sleep 1
>>          echo $i >/sys/bus/pci/drivers/xhci_hcd/bind
>>         done
>
> Again, why do this at all?

I need to reset some of the USB devices after a suspend/resume cycle.
The problem is, that some of the USB devices are
handed over into a running VirtualBox VM and after
the suspend/resume they need to be virtually plugged out/in
so that the running Windows VM will reconnect them.

If you search in the internet, you will find many places
where this unbind/bind process is mentioned, e.g.:
https://askubuntu.com/questions/645/how-do-you-reset-a-usb-device-from-the-command-line
This procedure did worked in the past.

I think the main problem is, that it's somehow unexpected that
the SATA controllers are logically attached to the USB
controllers.
So, if you believe to unbind "just" the USB devices you
suddenly unbind SATA controllers too.

>> immediately leads to a non-functional system, because the discs
>> face I/O errors and will switch to read-only mode.
>
> Sure, the disks are gone, this is expected.

Ok.

>> Effectively I have to reboot the machine.
>
> I'm amazed it keeps working at all.

:-)

>> It's reproduceable for me on two completely different x86 machines with
>> different USB devices.
>
> What do you expect this to do instead?  You just disabled all block
> controllers in your system, followed by all USB controllers.  And then
> attempted to add them back, but given that the old devices still had
> userspace references on them, the devices will come back with different
> names and so you need to mount them again.
>
> So this looks like it is working as intended.  Just don't do this :)

Ok, sure, but I think it's unexpected that the SATA ports are listed
beneath the USB controllers, beside USB devices.
If I run "lsusb", the SATA controllers don't show up either.
They are listed when I run "lspci".
Shouldn't they maybe show up somewhere else, e.g.
/sys/bus/pci/drivers/sata/*

Helge