tty: tty_port: Change the buffer allocator locking

We want to be able to do this without regard for the activate/own open
method being used which causes a problem using port->mutex. Add another
mutex for now. Once everything uses port_open to do buffer allocs we can
kill it back off

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/char/tty_port.c

diff --git a/drivers/char/tty_port.c b/drivers/char/tty_port.c
index dd471d6..3ef644a 100644
--- a/drivers/char/tty_port.c
+++ b/drivers/char/tty_port.c
@@ -25,6 +25,7 @@
 	init_waitqueue_head(&port->close_wait);
 	init_waitqueue_head(&port->delta_msr_wait);
 	mutex_init(&port->mutex);
+	mutex_init(&port->buf_mutex);
 	spin_lock_init(&port->lock);
 	port->close_delay = (50 * HZ) / 100;
 	port->closing_wait = (3000 * HZ) / 100;
@@ -34,10 +35,10 @@
 int tty_port_alloc_xmit_buf(struct tty_port *port)
 {
 	/* We may sleep in get_zeroed_page() */
-	mutex_lock(&port->mutex);
+	mutex_lock(&port->buf_mutex);
 	if (port->xmit_buf == NULL)
 		port->xmit_buf = (unsigned char *)get_zeroed_page(GFP_KERNEL);
-	mutex_unlock(&port->mutex);
+	mutex_unlock(&port->buf_mutex);
 	if (port->xmit_buf == NULL)
 		return -ENOMEM;
 	return 0;
@@ -46,12 +47,12 @@
 
 void tty_port_free_xmit_buf(struct tty_port *port)
 {
-	mutex_lock(&port->mutex);
+	mutex_lock(&port->buf_mutex);
 	if (port->xmit_buf != NULL) {
 		free_page((unsigned long)port->xmit_buf);
 		port->xmit_buf = NULL;
 	}
-	mutex_unlock(&port->mutex);
+	mutex_unlock(&port->buf_mutex);
 }
 EXPORT_SYMBOL(tty_port_free_xmit_buf);
 

include/linux/tty.h

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 6352ac2..e9269ca 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -212,6 +212,7 @@
 	wait_queue_head_t	delta_msr_wait;	/* Modem status change */
 	unsigned long		flags;		/* TTY flags ASY_*/
 	struct mutex		mutex;		/* Locking */
+	struct mutex		buf_mutex;	/* Buffer alloc lock */
 	unsigned char		*xmit_buf;	/* Optional buffer */
 	unsigned int		close_delay;	/* Close port delay */
 	unsigned int		closing_wait;	/* Delay for output */