- /* when lock_kernel() usage is fixed in usb_open(),
- * we could also fix it here */
+ /*
+ * BKL here is used to avoid race after usb_register_dev().
+ * Once the device node has been created, open() could happen on it.
+ * The code below will then fail, as hiddev_table hasn't been
+ * updated.
+ *
+ * The obvious fix -- introducing mutex to guard hiddev_table[]
+ * doesn't work, as usb_open() and usb_register_dev() both take
+ * minor_rwsem, thus we'll have ABBA deadlock.
+ *
+ * Before BKL pushdown, usb_open() had been acquiring it in right
+ * order, so _open() was safe to use it to protect from this race.
+ * Now the order is different, but AB-BA deadlock still doesn't occur
+ * as BKL is dropped on schedule() (i.e. while sleeping on
+ * minor_rwsem). Fugly.
+ */