Analysis:
========

(1) During TRUNCATE of file_per_table tablespace, dict_operation_lock is
released before eviction of dirty pages of a tablespace from the buffer
pool. After eviction, we try to re-acquire
dict_operation_lock (higher level latch) but we already hold lower
level latch (index->lock). This causes latch order violation

(2) Deadlock issue is present if child table is being truncated and it
holds index lock. At the same time, cascade dml happens and it took
dict_operation_lock and waiting for index lock.

Fix:
====
1) Release the indexes lock before releasing the dict operation lock.

2) Ignore the cascading dml operation on the parent table, for the
cascading foreign key, if the child table is truncated or if it is
in the process of being truncated.
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
Reviewed-by: Kevin Lewis <kevin.lewis@oracle.com>
RB: 16122