IB/ipath: fix race with exposing reset file

We were accidentally exposing the "reset" sysfs file more than once
per device.

Signed-off-by: Bryan O'Sullivan <bos@pathscale.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/ipath/ipath_diag.c

@@ -277,13 +277,14 @@ static int ipath_diag_open(struct inode *in, struct file *fp)
 
 bail:
 	spin_unlock_irqrestore(&ipath_devs_lock, flags);
-	mutex_unlock(&ipath_mutex);
 
 	/* Only expose a way to reset the device if we
 	   make it into diag mode. */
 	if (ret == 0)
 		ipath_expose_reset(&dd->pcidev->dev);
 
+	mutex_unlock(&ipath_mutex);
+
 	return ret;
 }
 

drivers/infiniband/hw/ipath/ipath_sysfs.c

@@ -711,10 +711,22 @@ static struct attribute_group dev_attr_group = {
  * enters diag mode.  A device reset is quite likely to crash the
  * machine entirely, so we don't want to normally make it
  * available.
+ *
+ * Called with ipath_mutex held.
  */
 int ipath_expose_reset(struct device *dev)
 {
-	return device_create_file(dev, &dev_attr_reset);
+	static int exposed;
+	int ret;
+
+	if (!exposed) {
+		ret = device_create_file(dev, &dev_attr_reset);
+		exposed = 1;
+	}
+	else
+		ret = 0;
+
+	return ret;
 }
 
 int ipath_driver_create_group(struct device_driver *drv)