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/rp2.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/rp2.c b/drivers/tty/serial/rp2.c index a314a94..328d6de 100644 --- a/drivers/tty/serial/rp2.c +++ b/drivers/tty/serial/rp2.c @@ -427,7 +427,9 @@ static void rp2_rx_chars(struct rp2_uart_port *up) up->port.icount.rx++; }
+ spin_unlock(&up->port.lock); tty_flip_buffer_push(port); + spin_lock(&up->port.lock); }
static void rp2_tx_chars(struct rp2_uart_port *up)