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/lpc32xx_hs.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/tty/serial/lpc32xx_hs.c b/drivers/tty/serial/lpc32xx_hs.c index 8fdf6a8..701644f 100644 --- a/drivers/tty/serial/lpc32xx_hs.c +++ b/drivers/tty/serial/lpc32xx_hs.c @@ -279,7 +279,10 @@ static void __serial_lpc32xx_rx(struct uart_port *port)
tmp = readl(LPC32XX_HSUART_FIFO(port->membase)); } + + spin_unlock(&port->lock); tty_flip_buffer_push(tport); + spin_lock(&port->lock); }
static void __serial_lpc32xx_tx(struct uart_port *port)