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/sa1100.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c index af6b3e3..28d60ef 100644 --- a/drivers/tty/serial/sa1100.c +++ b/drivers/tty/serial/sa1100.c @@ -232,7 +232,10 @@ sa1100_rx_chars(struct sa1100_port *sport) status = UTSR1_TO_SM(UART_GET_UTSR1(sport)) | UTSR0_TO_SM(UART_GET_UTSR0(sport)); } + + spin_unlock(&sport->port.lock); tty_flip_buffer_push(&sport->port.state->port); + spin_lock(&sport->port.lock); }
static void sa1100_tx_chars(struct sa1100_port *sport)