serial: core: Remove unsafe x_char optimization

uart_unthrottle() attempts to avoid sending START and the previous
x_char if the previous x_char has not yet been sent. However, this
optimization could leave the sender in a throttled state; for example,
if the sender is throttled and this unthrottle coincides with a manual
tcflow(TCION) from user-space, then neither START would be sent.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index bd20cf51e912c326d67f02631b078035d20b15b4..bdc543caf069a6f4a4d1dfa18f7309d44f15e02b 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -647,12 +647,8 @@ static void uart_unthrottle(struct tty_struct *tty)
                mask &= ~port->flags;
        }
 
-       if (mask & UPF_SOFT_FLOW) {
-               if (port->x_char)
-                       port->x_char = 0;
-               else
-                       uart_send_xchar(tty, START_CHAR(tty));
-       }
+       if (mask & UPF_SOFT_FLOW)
+               uart_send_xchar(tty, START_CHAR(tty));
 
        if (mask & UPF_HARD_FLOW)
                uart_set_mctrl(port, TIOCM_RTS);