[PATCH 1/5] TTY: serial, use ASYNCB_CLOSING in uart_close

Jiri Slaby
2011-08-25T13:12:25Z

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@suse.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