"ERROR: latch already owned" on gharial

Hi,

A couple of recent isolation test failures reported $SUBJECT.

It could be a bug in recent-ish latch refactoring work, though I don't
know why it would show up twice just recently.

Just BTW, that animal has shown signs of a flaky toolchain before[1].
I know we have quite a lot of museum exhibits in the 'farm, in terms
of hardare, OS, and tool chain.  In some cases, they're probably just
forgotten/not on anyone's upgrade radar.  If they've shown signs of
misbehaving, maybe it's time to figure out if they can be upgraded?
For example, it'd be nice to be able to rule out problems in GCC 4.6.0
(that's like running PostgreSQL 9.1.0, in terms of vintage,
unsupported status, and long list of missing bugfixes from the time
when it was supported).

[1] https://www.postgresql.org/message-id/CA+hUKGJK5R0S1LL_W4vEzKxNQGY_xGAQ1XknR-WN9jqQeQtB_w@mail.gmail.com