Re: Memory ordering issue in LWLockRelease, WakeupWaiters, WALInsertSlotRelease

On 2014-02-15 16:18:00 +0100, Andres Freund wrote:
> On 2014-02-15 10:06:41 -0500, Tom Lane wrote:
> > Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > > My current conclusion is that backporting barriers.h is by far the most
> > > reasonable way to go. The compiler problems have been ironed out by
> > > now...
> >
> > -1. IMO that code is still quite unproven, and what's more, the
> > problem we're discussing here is completely hypothetical. If it
> > were real, we'd have field evidence of it. We've not had that
> > much trouble seeing instances of even very narrow race-condition
> > windows in the past.
>
> Well, the problem is that few of us have access to interesting !x86
> machines to run tests, and that's where we'd see problems (since x86
> gives enough guarantees to avoid this unless the compiler reorders
> stuff). I am personally fine with just using volatiles to avoid
> reordering in the older branches, but Florian argued against it.

Here's patches doing that. The 9.3 version also applies to 9.2; the 9.1
version applies back to 8.4.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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