[PATCH 12/25] tty: serial: m32r_sio: drop uart_port->lock before calling tty_flip_buffer_push()

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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@xxxxxxxxxxxxx>
Date:   Tue May 29 21:53:50 2007 +0100

    [ARM] 4417/1: Serial: Fix AMBA drivers locking

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
 drivers/tty/serial/m32r_sio.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/m32r_sio.c b/drivers/tty/serial/m32r_sio.c
index bb1afa0..9cd9b4e 100644
--- a/drivers/tty/serial/m32r_sio.c
+++ b/drivers/tty/serial/m32r_sio.c
@@ -368,7 +368,10 @@ static void receive_chars(struct uart_sio_port *up, int *status)
 	ignore_char:
 		*status = serial_in(up, UART_LSR);
 	} while ((*status & UART_LSR_DR) && (max_count-- > 0));
+
+	spin_unlock(&up->port.lock);
 	tty_flip_buffer_push(port);
+	spin_lock(&up->port.lock);
 }
 
 static void transmit_chars(struct uart_sio_port *up)
-- 
1.7.12.rc2.18.g61b472e

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