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
Cc: Tobias Klauser tklauser@distanz.ch Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/tty/serial/altera_jtaguart.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/altera_jtaguart.c b/drivers/tty/serial/altera_jtaguart.c index c6bdb94..46c25ff 100644 --- a/drivers/tty/serial/altera_jtaguart.c +++ b/drivers/tty/serial/altera_jtaguart.c @@ -139,7 +139,9 @@ static void altera_jtaguart_rx_chars(struct altera_jtaguart *pp) uart_insert_char(port, 0, 0, ch, flag); }
+ spin_unlock(&port->lock); tty_flip_buffer_push(&port->state->port); + spin_lock(&port->lock); }
static void altera_jtaguart_tx_chars(struct altera_jtaguart *pp)