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

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Date:   Sun, 23 Jan 2022 14:11:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Helge Deller <deller@....de>
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 Sun, Jan 23, 2022 at 02:07:24PM +0100, Helge Deller wrote:
> On 1/23/22 13:33, Greg Kroah-Hartman wrote:
> > On Sun, Jan 23, 2022 at 12:59:21PM +0100, Helge Deller wrote:
> >> 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 devices, or the host controllers?  They are different things.
> >
> >> 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.
> >
> > unbind/bind is a very harsh way of doing this.  but do it on the USB
> > devics, not the host controllers.
> >
> >> 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.
> >
> > Never trust the internet :)
> >
> > But note, there is a usbreset program mentioned there, which is part of
> > 'usbutils' and should already be installed on your machine.  Why not
> > just use that?
> >
> >> I think the main problem is, that it's somehow unexpected that
> >> the SATA controllers are logically attached to the USB
> >> controllers.
> >
> > Huh?  No they are not.
> >
> > 'ahci' is a SATA controller.
> > 'xhci' is a USB controller.
> >
> > Two totally different things.
> 
> Right, and that was my fault.
> I mixed up "ahci" and "ehci" (the USB2.0 controller).

No worries, but please, do not just disable the USB host controllers
like this as well, as that will tear down, and then build back up the
whole USB device trees.  Any device that has anything open/running with
it will get confused.

good luck!

greg k-h