Comment 56 for bug 1640518

Ahh, if you're never actually seeing a SEGV in __lll_unlock_elision, this may indeed be something far more subtle than a double unlock and, in fact, I'd be even MORE interested in having you run the same batch of testing on an otherwise identical (ie: Ubuntu 16.04, blah blah blah) Skylake system.

It may well be a subtle glibc bug on powerpc, or a whackadoo silicon bug, or a more generic glibc bug or still a mongo bug, but the more data we can scrape up (I mean, unless you accidentally stumble on the bug in the process and fix it, then yay), the better.