On Fri, Oct 15, 2021 at 01:14:20PM +0200, Johan Hovold wrote:
Commit 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") added a hack to support SoCs where the UART reference clock can change behind the back of the driver but failed to add the proper locking.
First, make sure to take a reference to the tty struct to avoid dereferencing a NULL pointer if the clock change races with a hangup.
Second, the termios semaphore must be held during the update to prevent a racing termios change.
Nice catch! Thanks, Johan, for fixing this! Acked-by: Andy Shevchenko andriy.shevchenko@linux.intel.com
Fixes: 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") Fixes: c8dff3aa8241 ("serial: 8250: Skip uninitialized TTY port baud rate update") Cc: stable@vger.kernel.org # 5.9 Cc: Serge Semin Sergey.Semin@baikalelectronics.ru Signed-off-by: Johan Hovold johan@kernel.org
drivers/tty/serial/8250/8250_port.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 66374704747e..e4dd82fd7c2a 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2696,21 +2696,32 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) { struct uart_8250_port *up = up_to_u8250p(port);
- struct tty_port *tport = &port->state->port; unsigned int baud, quot, frac = 0; struct ktermios *termios;
- struct tty_struct *tty; unsigned long flags;
- mutex_lock(&port->state->port.mutex);
- tty = tty_port_tty_get(tport);
- if (!tty) {
mutex_lock(&tport->mutex);port->uartclk = uartclk;mutex_unlock(&tport->mutex);return;- }
- down_write(&tty->termios_rwsem);
- mutex_lock(&tport->mutex);
if (port->uartclk == uartclk) goto out_lock; port->uartclk = uartclk;
- if (!tty_port_initialized(&port->state->port))
- if (!tty_port_initialized(tport)) goto out_lock;
- termios = &port->state->port.tty->termios;
- termios = &tty->termios;
baud = serial8250_get_baud_rate(port, termios, NULL); quot = serial8250_get_divisor(port, baud, &frac); @@ -2727,7 +2738,9 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) serial8250_rpm_put(up); out_lock:
- mutex_unlock(&port->state->port.mutex);
- mutex_unlock(&tport->mutex);
- up_write(&tty->termios_rwsem);
- tty_kref_put(tty);
} EXPORT_SYMBOL_GPL(serial8250_update_uartclk); -- 2.32.0