usbdev: BKL pushdown

Add explicit lock_kernel() calls to usbdev_open()
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

drivers/usb/core/devio.c

@@ -565,6 +565,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
 	struct dev_state *ps;
 	int ret;
 
+	lock_kernel();
 	/* Protect against simultaneous removal or release */
 	mutex_lock(&usbfs_mutex);
 
@@ -611,6 +612,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
 	if (ret)
 		kfree(ps);
 	mutex_unlock(&usbfs_mutex);
+	unlock_kernel();
 	return ret;
 }