[PATCH 4.14 205/242] USB: serial: keyspan_pda: fix write unthrottling

Greg Kroah-Hartman
2020-12-28T13:19:00Z

From: Johan Hovold <johan@kernel.org>

commit 320f9028c7873c3c7710e8e93e5c979f4c857490 upstream.

The driver did not update its view of the available device buffer space
until write() was called in task context. This meant that write_room()
would return 0 even after the device had sent a write-unthrottle
notification, something which could lead to blocked writers not being
woken up (e.g. when using OPOST).

Note that we must also request an unthrottle notification is case a
write() request fills the device buffer exactly.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
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 | 29 ++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)

--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -44,6 +44,8 @@
#define DRIVER_AUTHOR "Brian Warner <warner@lothar.com>"
#define DRIVER_DESC "USB Keyspan PDA Converter driver"

+#define KEYSPAN_TX_THRESHOLD 16
+
struct keyspan_pda_private {
int tx_room;
int tx_throttled;
@@ -114,7 +116,7 @@ static void keyspan_pda_request_unthrott
7, /* request_unthrottle */
USB_TYPE_VENDOR | USB_RECIP_INTERFACE
| USB_DIR_OUT,
- 16, /* value: threshold */
+ KEYSPAN_TX_THRESHOLD,
0, /* index */
NULL,
0,
@@ -133,6 +135,8 @@ static void keyspan_pda_rx_interrupt(str
int retval;
int status = urb->status;
struct keyspan_pda_private *priv;
+ unsigned long flags;
+
priv = usb_get_serial_port_data(port);

switch (status) {
@@ -175,7 +179,10 @@ static void keyspan_pda_rx_interrupt(str
case 1: /* modemline change */
break;
case 2: /* tx unthrottle interrupt */
+ spin_lock_irqsave(&port->lock, flags);
priv->tx_throttled = 0;
+ priv->tx_room = max(priv->tx_room, KEYSPAN_TX_THRESHOLD);
+ spin_unlock_irqrestore(&port->lock, flags);
/* queue up a wakeup at scheduler time */
usb_serial_port_softint(port);
break;
@@ -509,7 +516,8 @@ static int keyspan_pda_write(struct tty_
goto exit;
}
}
- if (count > priv->tx_room) {
+
+ if (count >= priv->tx_room) {
/* we're about to completely fill the Tx buffer, so
we'll be throttled afterwards. */
count = priv->tx_room;
@@ -564,14 +572,17 @@ static void keyspan_pda_write_bulk_callb
static int keyspan_pda_write_room(struct tty_struct *tty)
{
struct usb_serial_port *port = tty->driver_data;
- struct keyspan_pda_private *priv;
- priv = usb_get_serial_port_data(port);
- /* used by n_tty.c for processing of tabs and such. Giving it our
- conservative guess is probably good enough, but needs testing by
- running a console through the device. */
- return priv->tx_room;
-}
+ struct keyspan_pda_private *priv = usb_get_serial_port_data(port);
+ unsigned long flags;
+ int room = 0;
+
+ spin_lock_irqsave(&port->lock, flags);
+ if (test_bit(0, &port->write_urbs_free) && !priv->tx_throttled)
+ room = priv->tx_room;
+ spin_unlock_irqrestore(&port->lock, flags);

+ return room;
+}

static int keyspan_pda_chars_in_buffer(struct tty_struct *tty)
{