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.
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.