2 files changed, 23 insertions, 6 deletions
diff --git a/drivers/char/xillybus/xillybus_class.c b/drivers/char/xillybus/xillybus_class.c
index 0f238648dcfe..e9a288e61c15 100644
--- a/drivers/char/xillybus/xillybus_class.c
+++ b/drivers/char/xillybus/xillybus_class.c
@@ -227,14 +227,15 @@ int xillybus_find_inode(struct inode *inode,
 			break;
 		}
 
-	mutex_unlock(&unit_mutex);
-
-	if (!unit)
+	if (!unit) {
+		mutex_unlock(&unit_mutex);
 		return -ENODEV;
+	}
 
 	*private_data = unit->private_data;
 	*index = minor - unit->lowest_minor;
 
+	mutex_unlock(&unit_mutex);
 	return 0;
 }
 EXPORT_SYMBOL(xillybus_find_inode);
diff --git a/drivers/char/xillybus/xillyusb.c b/drivers/char/xillybus/xillyusb.c
index 39bcbfd908b4..5a5afa14ca8c 100644
--- a/drivers/char/xillybus/xillyusb.c
+++ b/drivers/char/xillybus/xillyusb.c
@@ -184,6 +184,14 @@ struct xillyusb_dev {
 	struct mutex process_in_mutex; /* synchronize wakeup_all() */
 };
 
+/*
+ * kref_mutex is used in xillyusb_open() to prevent the xillyusb_dev
+ * struct from being freed during the gap between being found by
+ * xillybus_find_inode() and having its reference count incremented.
+ */
+
+static DEFINE_MUTEX(kref_mutex);
+
 /* FPGA to host opcodes */
 enum {
 	OPCODE_DATA = 0,
@@ -1237,9 +1245,16 @@ static int xillyusb_open(struct inode *inode, struct file *filp)
 	int rc;
 	int index;
 
+	mutex_lock(&kref_mutex);
+
 	rc = xillybus_find_inode(inode, (void **)&xdev, &index);
-	if (rc)
+	if (rc) {
+		mutex_unlock(&kref_mutex);
 		return rc;
+	}
+
+	kref_get(&xdev->kref);
+	mutex_unlock(&kref_mutex);
 
 	chan = &xdev->channels[index];
 	filp->private_data = chan;
@@ -1275,8 +1290,6 @@ static int xillyusb_open(struct inode *inode, struct file *filp)
 	    ((filp->f_mode & FMODE_WRITE) && chan->open_for_write))
 		goto unmutex_fail;
 
-	kref_get(&xdev->kref);
-
 	if (filp->f_mode & FMODE_READ)
 		chan->open_for_read = 1;
 
@@ -1413,6 +1426,7 @@ unopen:
 	return rc;
 
 unmutex_fail:
+	kref_put(&xdev->kref, cleanup_dev);
 	mutex_unlock(&chan->lock);
 	return rc;
 }
@@ -2227,7 +2241,9 @@ static void xillyusb_disconnect(struct usb_interface *interface)
 
 	xdev->dev = NULL;
 
+	mutex_lock(&kref_mutex);
 	kref_put(&xdev->kref, cleanup_dev);
+	mutex_unlock(&kref_mutex);
 }
 
 static struct usb_driver xillyusb_driver = {