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/apbuart.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/apbuart.c b/drivers/tty/serial/apbuart.c index 6331464d..de11ab8 100644 --- a/drivers/tty/serial/apbuart.c +++ b/drivers/tty/serial/apbuart.c @@ -125,7 +125,9 @@ static void apbuart_rx_chars(struct uart_port *port) status = UART_GET_STATUS(port); }
+ spin_unlock(&port->lock); tty_flip_buffer_push(&port->state->port); + spin_lock(&port->lock); }
static void apbuart_tx_chars(struct uart_port *port)