xhci: dbgtty: fix device unregister

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_vhangup() call in xhci_dbc_tty_unregister_device().
The tty_vhangup() wakes up any blocked writers and causes subsequent
write attempts to DbC terminal device to fail.

Cc: stable <stable@kernel.org>
Fixes: dfba217 ("usb: xhci: Add DbC support in xHCI driver")
Signed-off-by: Łukasz Bartosik <ukaszb@chromium.org>
Link: https://patch.msgid.link/20251119212910.1245694-1-ukaszb@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Łukasz Bartosik

drivers/usb/host/xhci-dbgtty.c

@@ -550,6 +550,12 @@ 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.
+	 */
+	tty_vhangup(port->port.tty);
+
 	tty_unregister_device(dbc_tty_driver, port->minor);
 	xhci_dbc_tty_exit_port(port);
 	port->registered = false;