USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)

USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)

[Ko, Kang Jun]

Hello,

I am reporting an USB related issue on the Linux Kernel version 5.15.71
Below is an error message that is seen in my dmesg log when my network switch goes into reboot. 

/****** Reboot log ******/
...
Reboot reason: Reboot requested by user
reboot: Restarting system
ftdi_sio ttyUSB0: usb_serial_generic_write_start - error submitting urb: -19
...
/****** Reboot log ******/

Summary:
Our network switch has two serial consoles attached to the system (one connected to the processor, one connected to FTDI chip).
When the switch goes into reboot, I can see (from the console connected to the processor) the above error message.
There is no functional problem in rebooting the switch but I would like to know if the error message is something intended by the Linux Kernel.

Reproduction steps:
Attach two serial consoles to the system and reboot.

Additional notes:
The serial drivers do not have a designated "shutdown" method so the driver is still present when the kernel goes through the device_shutdown method within the kernel_restart_prepare() function. The ftdi_sio serial driver continues to submit URB messages to the console when the console is already removed from the system, which results in the error message.

Conclusion:
Although this is not a functional issue and is not observed on systems with one serial console attached, this error message can be seen 100% on reboot on devices with multiple consoles. I would like to know if this error log is intended by design or if it is something that was not considered because there is no functional issue.

Thank you,
Jun Ko

Re: USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)

[Greg KH]

On Thu, Sep 18, 2025 at 08:39:11AM +0000, Ko, Kang Jun wrote:
> Hello,
> 
> I am reporting an USB related issue on the Linux Kernel version 5.15.71

Please note that that kernel is _VERY_ old and out of date and not
supported by anyone as it was released over 3 years ago.  There have
been over 19000 changes made to the 5.15.y branch since then.

Please try updating and see if the issue persists with the latest 5.15.y
release.

But, as you write:

> Below is an error message that is seen in my dmesg log when my network switch goes into reboot. 
> 
> /****** Reboot log ******/
> ...
> Reboot reason: Reboot requested by user
> reboot: Restarting system
> ftdi_sio ttyUSB0: usb_serial_generic_write_start - error submitting urb: -19
> ...
> /****** Reboot log ******/
> 
> Summary:
> Our network switch has two serial consoles attached to the system (one connected to the processor, one connected to FTDI chip).
> When the switch goes into reboot, I can see (from the console connected to the processor) the above error message.
> There is no functional problem in rebooting the switch but I would like to know if the error message is something intended by the Linux Kernel.
> 
> Reproduction steps:
> Attach two serial consoles to the system and reboot.
> 
> Additional notes:
> The serial drivers do not have a designated "shutdown" method so the driver is still present when the kernel goes through the device_shutdown method within the kernel_restart_prepare() function. The ftdi_sio serial driver continues to submit URB messages to the console when the console is already removed from the system, which results in the error message.
> 
> Conclusion:
> Although this is not a functional issue and is not observed on systems with one serial console attached, this error message can be seen 100% on reboot on devices with multiple consoles. I would like to know if this error log is intended by design or if it is something that was not considered because there is no functional issue.

This really isn't a bug, and you should be able to just ignore it, the
kernel is correctly noting that it could not submit the USB message
because the hardware has gone away and you did not close the console
before that happened.

But again, PLEASE update your kernel, it is very old and full of known
security issues that have been resolved already.

thanks,

greg k-h

Re: USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)

[Ko, Kang Jun]

Hello,

Thank you for the kind response. I've tried updating the kernel version to 6.12.3
and the same error message still exists during shutdown.

I understand this is not a bug or a functional issue and the kernel is correctly noting that the hardware is no longer reachable.
 
However, I would like to know if canceling the USB messages when the hardware has gone away so that the error message doesn't happen is something that is considered for future kernel versions.

Thank you,
Jun Ko


________________________________________
From: Greg KH <gregkh@linuxfoundation.org>
Sent: Thursday, September 18, 2025 5:09 PM
To: Ko, Kang Jun <kang-jun.ko@hpe.com>
Cc: linux-usb@vger.kernel.org <linux-usb@vger.kernel.org>
Subject: Re: USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)


On Thu, Sep 18, 2025 at 08:39:11AM +0000, Ko, Kang Jun wrote:
> Hello,
> 
> I am reporting an USB related issue on the Linux Kernel version 5.15.71

Please note that that kernel is _VERY_ old and out of date and not
supported by anyone as it was released over 3 years ago.  There have
been over 19000 changes made to the 5.15.y branch since then.

Please try updating and see if the issue persists with the latest 5.15.y
release.

But, as you write:

> Below is an error message that is seen in my dmesg log when my network switch goes into reboot. 
> 
> /****** Reboot log ******/
> ...
> Reboot reason: Reboot requested by user
> reboot: Restarting system
> ftdi_sio ttyUSB0: usb_serial_generic_write_start - error submitting urb: -19
> ...
> /****** Reboot log ******/
> 
> Summary:
> Our network switch has two serial consoles attached to the system (one connected to the processor, one connected to FTDI chip).
> When the switch goes into reboot, I can see (from the console connected to the processor) the above error message.
> There is no functional problem in rebooting the switch but I would like to know if the error message is something intended by the Linux Kernel.
> 
> Reproduction steps:
> Attach two serial consoles to the system and reboot.
> 
> Additional notes:
> The serial drivers do not have a designated "shutdown" method so the driver is still present when the kernel goes through the device_shutdown method within the kernel_restart_prepare() function. The ftdi_sio serial driver continues to submit URB messages to the console when the console is already removed from the system, which results in the error message.
> 
> Conclusion:
> Although this is not a functional issue and is not observed on systems with one serial console attached, this error message can be seen 100% on reboot on devices with multiple consoles. I would like to know if this error log is intended by design or if it is something that was not considered because there is no functional issue.

This really isn't a bug, and you should be able to just ignore it, the
kernel is correctly noting that it could not submit the USB message
because the hardware has gone away and you did not close the console
before that happened.

But again, PLEASE update your kernel, it is very old and full of known
security issues that have been resolved already.

thanks,

greg k-h

Re: USB: urb error log during reboot on devices with multiple serial consoles (Linux Kernel version 5.15.71)

[Greg KH]

On Thu, Sep 25, 2025 at 01:29:57AM +0000, Ko, Kang Jun wrote:
> Hello,
> 
> Thank you for the kind response. I've tried updating the kernel version to 6.12.3
> and the same error message still exists during shutdown.
> 
> I understand this is not a bug or a functional issue and the kernel is correctly noting that the hardware is no longer reachable.
>  
> However, I would like to know if canceling the USB messages when the
> hardware has gone away so that the error message doesn't happen is
> something that is considered for future kernel versions.

The "problem" here is that the console does not seem to close the
backing tty device properly.  And that is required so that the usb
driver will shut down the submission of the urbs, which will prevent the
message you see from showing up.

The fact that a console works over a usb-serial device at all is a
wonderful hack.  It was me loosing a bet many years ago that even caused
that code to be written in the first place.  So if this even works is
amazing, a little bit of error messages when the device is yanked from
the system is a small price to pay for this feature :)

thanks,

greg k-h