Just to remind
Cold, hard experience.
Bug 2530125 Hang possible with "enqueue hash chains" latch held during deadlock detection
Or, as described to me by Oracle Support about 3 years ago, "Deadlock detection dumps the processstate while holding the 'parent+children enqueue hash chains' latch which can cause the blocking symptoms you describe while the processtate is dumped. "
Supposedly fixed in 126.96.36.199 and 10.1.0.2. I don't believe Sachin mentioned what version he was on.
holding a latch and doing file I/O ? Where did you get that idea?