[PATCH 4.19 292/346] USB: serial: keyspan_pda: fix write deadlock

Greg Kroah-Hartman
2020-12-28T15:55:48Z

From: Johan Hovold <johan@kernel.org>

commit 7353cad7ee4deaefc16e94727e69285563e219f6 upstream.

The write() callback can be called in interrupt context (e.g. when used
as a console) so interrupts must be disabled while holding the port lock
to prevent a possible deadlock.

Fixes: e81ee637e4ae ("usb-serial: possible irq lock inversion (PPP vs. usb/serial)")
Fixes: 507ca9bc0476 ("[PATCH] USB: add ability for usb-serial drivers to determine if their write urb is currently being used.")
Cc: stable <stable@vger.kernel.org> # 2.6.19
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/serial/keyspan_pda.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -443,6 +443,7 @@ static int keyspan_pda_write(struct tty_
int request_unthrottle = 0;
int rc = 0;
struct keyspan_pda_private *priv;
+ unsigned long flags;

priv = usb_get_serial_port_data(port);
/* guess how much room is left in the device's ring buffer, and if we
@@ -462,13 +463,13 @@ static int keyspan_pda_write(struct tty_
the TX urb is in-flight (wait until it completes)
the device is full (wait until it says there is room)
*/
- spin_lock_bh(&port->lock);
+ spin_lock_irqsave(&port->lock, flags);
if (!test_bit(0, &port->write_urbs_free) || priv->tx_throttled) {
- spin_unlock_bh(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);
return 0;
}
clear_bit(0, &port->write_urbs_free);
- spin_unlock_bh(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);

/* At this point the URB is in our control, nobody else can submit it
again (the only sudden transition was the one from EINPROGRESS to