RFR(S): JDK-8129108: nmethod related crash in CMS

[Mikael Gerdin]

Poonam,

On 2015-06-20 06:32, Poonam Bajaj Parhar wrote:
> Hello,
>
> Please review this change for bug:
> JDK-8129108: <https://bugs.openjdk.java.net/browse/JDK-8129108> nmethod
> related crash in CM
>
> There is an assertion failure with fastdebug build with test
> /nsk.coverage.arguments.arguments002.arguments002/.
> This failure occurs when CMSCollector::_should_unload_classes is false
> and the _roots_scanning_options does
> not contain SO_AllCodeCache:
>
> #  Internal Error (hotspot/src/share/vm/gc/cms/concurrentMarkSweepGeneration.cpp:4472), pid=16267, tid=0xf36ffb70
> #  assert(_collector->should_unload_classes() ||
> (_collector->CMSCollector::roots_scanning_options() &
> GenCollectedHeap::SO_AllCodeCache)) failed: if we didn't scan the code
> cache, we have to be ready to drop nmethods with expired weak oops
>
>
> This problem was exposed with the fix ofJDK-8085965:
> <https://bugs.openjdk.java.net/browse/JDK-8085965> VM hangs in C2Compiler,
> that disables CMSClassUnloadingEnabled when -Xnoclassgc or
> -XX:-ClassUnloading
> are specified on the command line.
>
> CMSCollector::_roots_scanning_options option should contain
> SO_AllCodeCache to ensure
> that we scan code cache when we are not unloading classes.
>
> Webrev: http://cr.openjdk.java.net/~poonam/8129108/webrev/

This looks very similar to the code in 
CMSCollector::setup_cms_unloading_and_verification_state
which is called from CMSCollector::checkpointRootsInitialWork

I think that the if-clause in setup_cms_unloading... needs to be fixed 
to handle the class unloading case separately from the verification state.
It's not entirely clear to me exactly which cases the complicated 
conditions in the if statements try to capture, though. You may want to 
look at a previous version of the sources (before perm gen removal) to 
better understand the reasoning behind it.

/Mikael

> Testing: JPRT, testcase /nsk.coverage.arguments.arguments002.arguments002/
>
> Thanks,
> Poonam
>