[PATCH v1] xhci: dbgtty: fix device unregister

["Łukasz Bartosik" <ukaszb@chromium.org>]

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.

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);
+
 	tty_unregister_device(dbc_tty_driver, port->minor);
 	xhci_dbc_tty_exit_port(port);
 	port->registered = false;
-- 
2.52.0.rc1.455.g30608eb744-goog