Re: [PATCH v1] xhci: dbgtty: fix device unregister

[Mathias Nyman <mathias.nyman@linux.intel.com>]

Hi Łukasz

On 11/14/25 17:01, Łukasz Bartosik wrote:
> From: Łukasz Bartosik <ukaszb@chromium.org>
> 
> When DbC is disconnected then xhci_dbc_tty_unregister_device()
> is called. However if there is any user space process blocked
> on write to DbC terminal device then it will never be signalled
> and thus stay blocked indifinitely.
> 
> This fix adds a tty_hangup() call in xhci_dbc_tty_unregister_device().
> The tty_hangup() wakes up any blocked writers and causes subsequent
> write attempts to DbC terminal device to fail.

Nice catch

> 
> Cc: stable@vger.kernel.org
> Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
> Signed-off-by: Łukasz Bartosik <ukaszb@chromium.org>
> ---
>   drivers/usb/host/xhci-dbgtty.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-dbgtty.c b/drivers/usb/host/xhci-dbgtty.c
> index d894081d8d15..6ea31af576c7 100644
> --- a/drivers/usb/host/xhci-dbgtty.c
> +++ b/drivers/usb/host/xhci-dbgtty.c
> @@ -535,6 +535,13 @@ static void xhci_dbc_tty_unregister_device(struct xhci_dbc *dbc)
>   
>   	if (!port->registered)
>   		return;
> +	/*
> +	 * Hang up the TTY. This wakes up any blocked
> +	 * writers and causes subsequent writes to fail.
> +	 */
> +	if (port->port.tty)
> +		tty_hangup(port->port.tty);

I'm not a tty expert but would the tty_port_tty_vhangup(&port->port) make
sense here?

No need to check for port->port.tty, and it does all the needed locking and
tty reference counting.

It is also synchronous which should probably be ok as this is either called
from a delayed workqueue, during suspend, or remove()

Thanks
Mathias