releaseOk and LWLockWaitForVar

Hi Heikki, All,

Amit just pointed me to a case where the lwlock scalability patch
apparently causes problems and I went on to review it and came across
the following problem in 9.4/master:
LWLockWaitForVar() doesn't set releaseOk to true when waiting
again. Isn't that a bug? What if there's another locker coming in after
LWLockWaitForVar() returns from the PGSemaphoreLock() but before it has
acquire the spinlock? Now, it might be that it's unproblematic because
of hte specific way these locks are used right now, but it doesn't seem
like a good idea to leave it that way.

Greetings,

Andres Freund

-- Andres Freund	                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services