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/icom.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/tty/serial/icom.c b/drivers/tty/serial/icom.c index 18ed5ae..46cb597 100644 --- a/drivers/tty/serial/icom.c +++ b/drivers/tty/serial/icom.c @@ -834,7 +834,10 @@ ignore_char: status = cpu_to_le16(icom_port->statStg->rcv[rcv_buff].flags); } icom_port->next_rcv = rcv_buff; + + spin_unlock(&icom_port->uart_port.lock); tty_flip_buffer_push(port); + spin_lock(&icom_port->uart_port.lock); }
static void process_interrupt(u16 port_int_reg,