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: David Brown davidb@codeaurora.org (maintainer:ARM/QUALCOMM MSM...) Cc: Daniel Walker dwalker@fifo99.com (maintainer:ARM/QUALCOMM MSM...) Cc: Bryan Huntsman bryanh@codeaurora.org (maintainer:ARM/QUALCOMM MSM...) Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/tty/serial/msm_serial.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c index 2c6cfb3..daa2837 100644 --- a/drivers/tty/serial/msm_serial.c +++ b/drivers/tty/serial/msm_serial.c @@ -137,7 +137,10 @@ static void handle_rx_dm(struct uart_port *port, unsigned int misr) count -= 4; }
+ spin_unlock(&port->lock); tty_flip_buffer_push(tport); + spin_lock(&port->lock); + if (misr & (UART_IMR_RXSTALE)) msm_write(port, UART_CR_CMD_RESET_STALE_INT, UART_CR); msm_write(port, 0xFFFFFF, UARTDM_DMRX); @@ -189,7 +192,9 @@ static void handle_rx(struct uart_port *port) tty_insert_flip_char(tport, c, flag); }
+ spin_unlock(&port->lock); tty_flip_buffer_push(tport); + spin_lock(&port->lock); }
static void reset_dm_count(struct uart_port *port)