RFR (XS) 8229000: Fix lock and reenable assert in Monitor::check_safepoint_state

[David Holmes]

Hi Coleen,

On 2/08/2019 10:37 pm, coleen.phillimore at oracle.com wrote:
> There was only one place in CMS that violated the condition in the new 
> assert, fixed with this patch.  See linked bugs for details.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/2019/8229000.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8229000

The fix seems okay in the sense that we have a NonJavaThread and so 
should be using lock_without_safepoint_check(). But I'm a bit puzzled as 
the code you fixed is not what was failing in JDK-8223190 when the 
assert was removed. ??

Thanks,
David

> Ran mach5 hs-tier1-3 (all failed tests were in these tiers) on 
> linux-x64-debug, and tier1 on all Oracle platforms.
> 
> Thanks,
> Coleen