The -rt patch triggers a lockdep warning for serial drivers if tty_flip_buffer_push() is called with uart_port->lock locked. This never shows up on UP kernels.
Release the port lock before calling tty_flip_buffer_push() and reacquire it after the call.
Similar stuff was already done for few other drivers in the past, like:
commit 2389b272168ceec056ca1d8a870a97fa9c26e11a Author: Thomas Gleixner tglx@linutronix.de Date: Tue May 29 21:53:50 2007 +0100
[ARM] 4417/1: Serial: Fix AMBA drivers locking
Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/tty/serial/m32r_sio.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/tty/serial/m32r_sio.c b/drivers/tty/serial/m32r_sio.c index bb1afa0..9cd9b4e 100644 --- a/drivers/tty/serial/m32r_sio.c +++ b/drivers/tty/serial/m32r_sio.c @@ -368,7 +368,10 @@ static void receive_chars(struct uart_sio_port *up, int *status) ignore_char: *status = serial_in(up, UART_LSR); } while ((*status & UART_LSR_DR) && (max_count-- > 0)); + + spin_unlock(&up->port.lock); tty_flip_buffer_push(port); + spin_lock(&up->port.lock); }
static void transmit_chars(struct uart_sio_port *up)