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Subject[PATCH 05/26] serial: core: Remove unsafe x_char optimization
Date
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>
---
drivers/tty/serial/serial_core.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a68bff0..11c8fe6 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -643,12 +643,8 @@ 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);
--
2.1.0


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