USB: serial: keyspan_pda: fix dropped unthrottle interrupts

BugLink: https://bugs.launchpad.net/bugs/1910111
commit 696c541c8c6cfa05d65aa24ae2b9e720fc01766e upstream.

Commit c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity
checks") broke write-unthrottle handling by dropping well-formed
unthrottle-interrupt packets which are precisely two bytes long. This
could lead to blocked writers not being woken up when buffer space again
becomes available.

Instead, stop unconditionally printing the third byte which is
(presumably) only valid on modem-line changes.

Fixes: c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity checks")
Cc: stable <stable@vger.kernel.org>     # 4.11
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>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/drivers/usb/serial/keyspan_pda.c b/drivers/usb/serial/keyspan_pda.c
index c1333919716b67950e924e503d00384b53b0cebe..2d5ad579475a8417c09ce1218ba73b6f77c0b2ee 100644 (file)
--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -172,11 +172,11 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
                break;
        case 1:
                /* status interrupt */
-               if (len < 3) {
+               if (len < 2) {
                        dev_warn(&port->dev, "short interrupt message received\n");
                        break;
                }
-               dev_dbg(&port->dev, "rx int, d1=%d, d2=%d\n", data[1], data[2]);
+               dev_dbg(&port->dev, "rx int, d1=%d\n", data[1]);
                switch (data[1]) {
                case 1: /* modemline change */
                        break;