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/mcf.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/mcf.c b/drivers/tty/serial/mcf.c index 65be0c0..62c8fdf 100644 --- a/drivers/tty/serial/mcf.c +++ b/drivers/tty/serial/mcf.c @@ -324,7 +324,9 @@ static void mcf_rx_chars(struct mcf_uart *pp) uart_insert_char(port, status, MCFUART_USR_RXOVERRUN, ch, flag); }
+ spin_unlock(&port->lock); tty_flip_buffer_push(&port->state->port); + spin_lock(&port->lock); }
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