Re: acm_port_shutdown hangs for 30 seconds

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jun 28, 2022 at 07:21:48PM +1000, Jookia wrote:
> Hi Greg,
> 
> Thanks for getting back to this!
> 
> On Mon, Jun 27, 2022 at 02:57:17PM +0200, Greg KH wrote:
> > What host controller driver is this showing up on?
> 
> I have the following modules loaded:
> 
> xhci_pci_renesas
> xhci_pci
> xhci_hcd
> 
> This isn't an ARM board or anything, this is a standard x86 desktop
> (B450 plus motherboard, Ryzen 3700x chipset)- but I believe I've had the
> same error when using serial cables on a years older computer and in
> general when doing embedded development.
> 
> I believe this issue is related to buggy serial devices, in particular
> ones run by a microcontroller like an ATmega32u4 and perhaps Linux USB
> gadget where the device is abruptly reset but the serial session isn't
> terminated.
> 
> The host device USB system has to time out then, which is fine, but in
> userspace this seems to hang close() instead of doing this
> asynchronously.

The close is timing out as it tries to flush the data to the device
which is no longer responding.  So this kind of is expected behavior,
sorry.

greg k-h