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/arc_uart.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/arc_uart.c b/drivers/tty/serial/arc_uart.c index 22f280a..8cf6b30 100644 --- a/drivers/tty/serial/arc_uart.c +++ b/drivers/tty/serial/arc_uart.c @@ -248,7 +248,9 @@ static void arc_serial_rx_chars(struct arc_uart_port *uart) uart_insert_char(&uart->port, status, RXOERR, ch, flg);
done: + spin_unlock(&uart->port.lock); tty_flip_buffer_push(&uart->port.state->port); + spin_lock(&uart->port.lock); } }