[PATCH v3 3/4] serial: fix TIOCMIWAIT race
From: Johan Hovold
Date: Mon Sep 07 2026 - 02:47:06 EST
The task state must be updated before checking the wakeup condition to
avoid missing a racing modem status update.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: sashiko-bot@xxxxxxxxxx
Link: https://lore.kernel.org/r/20260904115542.E20D11F00A3D@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 4213fa3dc988..c2c2c8fe1a4c 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1230,12 +1230,12 @@ static int uart_wait_modem_status(struct tty_struct *tty, struct uart_state *sta
add_wait_queue(&port->delta_msr_wait, &wait);
for (;;) {
+ set_current_state(TASK_INTERRUPTIBLE);
+
uart_port_lock_irq(uport);
memcpy(&cnow, &uport->icount, sizeof(struct uart_icount));
uart_port_unlock_irq(uport);
- set_current_state(TASK_INTERRUPTIBLE);
-
if (((arg & TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
((arg & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
((arg & TIOCM_CD) && (cnow.dcd != cprev.dcd)) ||
--
2.55.0