Patch from Rohit Seth, changelog from Bill Irwin:

(1) fixes failure to clear key->busy (yes, it's always under a lock)
(2) fixes key->count being unconditionally set to 1 in alloc_key()
(3) reduces search to key->size >> HPAGE_SHIFT from key->size
(4) actually uses vma->vm_private_data to release the key as intended

plus the cleanup:
(5) removes the int *new argument to alloc_key()