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: Stephen Warren swarren@wwwdotorg.org Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/tty/serial/serial-tegra.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c index ee7c812..82846cf 100644 --- a/drivers/tty/serial/serial-tegra.c +++ b/drivers/tty/serial/serial-tegra.c @@ -571,7 +571,9 @@ static void tegra_uart_rx_dma_complete(void *args)
tegra_uart_handle_rx_pio(tup, port); if (tty) { + spin_unlock_irqrestore(&u->lock, flags); tty_flip_buffer_push(port); + spin_lock_irqsave(&u->lock, flags); tty_kref_put(tty); } tegra_uart_start_rx_dma(tup); @@ -583,11 +585,13 @@ static void tegra_uart_rx_dma_complete(void *args) spin_unlock_irqrestore(&u->lock, flags); }
-static void tegra_uart_handle_rx_dma(struct tegra_uart_port *tup) +static void tegra_uart_handle_rx_dma(struct tegra_uart_port *tup, + unsigned long *flags) { struct dma_tx_state state; struct tty_struct *tty = tty_port_tty_get(&tup->uport.state->port); struct tty_port *port = &tup->uport.state->port; + struct uart_port *u = &tup->uport; int count;
/* Deactivate flow control to stop sender */ @@ -604,7 +608,9 @@ static void tegra_uart_handle_rx_dma(struct tegra_uart_port *tup)
tegra_uart_handle_rx_pio(tup, port); if (tty) { + spin_unlock_irqrestore(&u->lock, *flags); tty_flip_buffer_push(port); + spin_lock_irqsave(&u->lock, *flags); tty_kref_put(tty); } tegra_uart_start_rx_dma(tup); @@ -671,7 +677,7 @@ static irqreturn_t tegra_uart_isr(int irq, void *data) iir = tegra_uart_read(tup, UART_IIR); if (iir & UART_IIR_NO_INT) { if (is_rx_int) { - tegra_uart_handle_rx_dma(tup); + tegra_uart_handle_rx_dma(tup, &flags); if (tup->rx_in_progress) { ier = tup->ier_shadow; ier |= (UART_IER_RLSI | UART_IER_RTOIE |