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Date:   Wed, 29 Jun 2022 10:37:55 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jookia <contact@jookia.org>
Cc:     linux-usb@vger.kernel.org
Subject: Re: acm_port_shutdown hangs for 30 seconds
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References: <YiynBKeGJCMEkgyO@novena-choice-citizen>
 <YrmpLXcPeHW4fnvz@kroah.com>
 <YrrILGzC2R3qGiHu@novena-choice-citizen>
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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