linux-kernel - [PATCH 1/5] TTY: serial, use ASYNCB_CLOSING in uart

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Date:	Thu, 25 Aug 2011 15:12:04 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	gregkh@...e.de
Cc:	Arnd Bergmann <arnd@...db.de>, alan@...ux.intel.com,
	linux-serial@...r.kernel.org, jirislaby@...il.com,
	linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 1/5] TTY: serial, use ASYNCB_CLOSING in uart_close

We need to move port->mutex locking after wait_until_sent in
uart_close (for rationale see next patches). But if we did it now, we
would introduce a race between close and open. This is exactly why
port->mutex is locked at the top of uart_close.

To avoid the race, we add ASYNCB_CLOSING to uart_close. Like every
other sane TTY driver. Thanks to tty_port_block_til_ready used in
uart_open we will have this for free. Then we can move the port->mutex
lock.

Also note that this will make the conversion to tty_port helpers
easier. They are currently handling ASYNC_CLOSING flag correctly.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/serial/serial_core.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 781d566..cd7a0bb 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1293,6 +1293,7 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
 	 * the line discipline to only process XON/XOFF characters by
 	 * setting tty->closing.
 	 */
+	set_bit(ASYNCB_CLOSING, &port->flags);
 	tty->closing = 1;
 	spin_unlock_irqrestore(&port->lock, flags);
 
@@ -1340,8 +1341,10 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
 	 * Wake up anyone trying to open this port.
 	 */
 	clear_bit(ASYNCB_NORMAL_ACTIVE, &port->flags);
+	clear_bit(ASYNCB_CLOSING, &port->flags);
 	spin_unlock_irqrestore(&port->lock, flags);
 	wake_up_interruptible(&port->open_wait);
+	wake_up_interruptible(&port->close_wait);
 
 done:
 	mutex_unlock(&port->mutex);
-- 
1.7.6


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