serial: core: Fix port count when uart_open() errors

A port count mismatch occurs if mutex_lock_interruptible()
exits uart_open() and the port has already been opened. This may
prematurely close a port on an open tty. Since uart_close() is _always_
called if uart_open() fails, the port count must be corrected if errors
occur.

Always increment the port count in uart_open(), regardless of errors;
always decrement the port count in uart_close(). Note that
tty_port_close_start() decrements the port count when uart_open()
was successful.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 0282eaaff517adba1fee25b6353d5b168c28ac23..3e36ecf98624d5574d3e3786b5e497f31c9697bf 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1338,8 +1338,16 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
        struct uart_port *uport;
        unsigned long flags;
 
-       if (!state)
+       if (!state) {
+               struct uart_driver *drv = tty->driver->driver_state;
+
+               state = drv->state + tty->index;
+               port = &state->port;
+               spin_lock_irq(&port->lock);
+               --port->count;
+               spin_unlock_irq(&port->lock);
                return;
+       }
 
        uport = state->uart_port;
        port = &state->port;
@@ -1556,6 +1564,10 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
 
        pr_debug("uart_open(%d) called\n", line);
 
+       spin_lock_irq(&port->lock);
+       ++port->count;
+       spin_unlock_irq(&port->lock);
+
        /*
         * We take the semaphore here to guarantee that we won't be re-entered
         * while allocating the state structure, or while we request any IRQs
@@ -1568,17 +1580,11 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
                goto end;
        }
 
-       port->count++;
        if (!state->uart_port || state->uart_port->flags & UPF_DEAD) {
                retval = -ENXIO;
-               goto err_dec_count;
+               goto err_unlock;
        }
 
-       /*
-        * Once we set tty->driver_data here, we are guaranteed that
-        * uart_close() will decrement the driver module use count.
-        * Any failures from here onwards should not touch the count.
-        */
        tty->driver_data = state;
        state->uart_port->state = state;
        state->port.low_latency =
@@ -1599,8 +1605,7 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
 
 end:
        return retval;
-err_dec_count:
-       port->count--;
+err_unlock:
        mutex_unlock(&port->mutex);
        goto end;
 }