RFR: 8274196: Crashes in VM_HeapDumper::work after JDK-8252842

[Coleen Phillimore]

On Fri, 24 Sep 2021 14:05:48 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> I think it may be because this is actually not a JavaThread. So the assert in `Mutex::check_no_safepoint_state` would pass. 
>> Moreover, I have tried to use `PaddedMonitor(Mutex::nosafepoint, "ParallelHProfWriter_lock", Mutex::_safepoint_check_never);` here, but the slowdebug would report errors as you mentioned in JDK-8274245.
>
> I agree the flag here and at the place of lock acquiring  seems problematic. I will try to see whether I can use `Mutex::_safepoint_check_never` here and get rid of the assert.

yes
    void Mutex::check_no_safepoint_state(Thread* thread) {
       check_block_state(thread);
       assert(!thread->is_active_Java_thread() || _safepoint_check_required != _safepoint_check_always,
              "This lock should always have a safepoint check for Java threads: %s",
              name());
     }

yes, we exclude the check for a non-java thread, which I thought was an odd exclusion last time I looked.  I pass the tests in sun/tools/jmap/BasicJMapTest.java so maybe leave it for now?

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PR: https://git.openjdk.java.net/jdk/pull/5681