USB: ftdi_sio: Replace BKL with a mutex

As Alan Cox have pinpointed the driver still required protection against
parallels calls to the config ioctl(). If lock is still necessary the use of
BKL is abused here. So replace BKL with a more convenient mutex.
Signed-off-by: Alessio Igor Bogani <abogani@texware.it>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Johan Hovold <jhovold@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Daniel Mack <daniel@caiaq.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/ftdi_sio.c

@@ -33,12 +33,12 @@
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/slab.h>
-#include <linux/smp_lock.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_flip.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include <linux/uaccess.h>
 #include <linux/usb.h>
 #include <linux/serial.h>
@@ -92,6 +92,7 @@ struct ftdi_private {
 	unsigned long tx_outstanding_bytes;
 	unsigned long tx_outstanding_urbs;
 	unsigned short max_packet_size;
+	struct mutex cfg_lock; /* Avoid mess by parallel calls of config ioctl() */
 };
 
 /* struct ftdi_sio_quirk is used by devices requiring special attention. */
@@ -1218,7 +1219,7 @@ static int set_serial_info(struct tty_struct *tty,
 	if (copy_from_user(&new_serial, newinfo, sizeof(new_serial)))
 		return -EFAULT;
 
-	lock_kernel();
+	mutex_lock(&priv->cfg_lock);
 	old_priv = *priv;
 
 	/* Do error checking and permission checking */
@@ -1226,7 +1227,7 @@ static int set_serial_info(struct tty_struct *tty,
 	if (!capable(CAP_SYS_ADMIN)) {
 		if (((new_serial.flags & ~ASYNC_USR_MASK) !=
 		     (priv->flags & ~ASYNC_USR_MASK))) {
-			unlock_kernel();
+			mutex_unlock(&priv->cfg_lock);
 			return -EPERM;
 		}
 		priv->flags = ((priv->flags & ~ASYNC_USR_MASK) |
@@ -1237,7 +1238,7 @@ static int set_serial_info(struct tty_struct *tty,
 
 	if ((new_serial.baud_base != priv->baud_base) &&
 	    (new_serial.baud_base < 9600)) {
-	    	unlock_kernel();
+		mutex_unlock(&priv->cfg_lock);
 		return -EINVAL;
 	}
 
@@ -1267,11 +1268,11 @@ static int set_serial_info(struct tty_struct *tty,
 	     (priv->flags & ASYNC_SPD_MASK)) ||
 	    (((priv->flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST) &&
 	     (old_priv.custom_divisor != priv->custom_divisor))) {
-		unlock_kernel();
+		mutex_unlock(&priv->cfg_lock);
 		change_speed(tty, port);
 	}
 	else
-		unlock_kernel();
+		mutex_unlock(&priv->cfg_lock);
 	return 0;
 
 } /* set_serial_info */
@@ -1538,6 +1539,7 @@ static int ftdi_sio_port_probe(struct usb_serial_port *port)
 
 	kref_init(&priv->kref);
 	spin_lock_init(&priv->tx_lock);
+	mutex_init(&priv->cfg_lock);
 	init_waitqueue_head(&priv->delta_msr_wait);
 
 	priv->flags = ASYNC_LOW_LATENCY;