On Fri, 24 Sep 2021 13:37:44 GMT, Coleen Phillimore <cole...@openjdk.org> wrote:
>> The root cause for crash in ZGC is that the JNIHandles are processed before
>> object iteration. And ZGC would update the JNIHandles at object iteration
>> with read barrier. So the crash is cause by accessing the invalid address
>> which can be dummy info after zgc, and hence crash.
>>
>> The lock rank issue can be fixed because the related mutexes are acquired in
>> safepoint. so the safepoint_check_required could be safepoint_check_always.
>>
>> The Epsilon issue is caused by wrong _num_dumper_thread calculated when the
>> gang==NULL.
>
> src/hotspot/share/services/heapDumper.cpp line 751:
>
>> 749: static void before_work() {
>> 750: assert(_lock == NULL, "ParDumpWriter lock must be initialized only
>> once");
>> 751: _lock = new (std::nothrow) PaddedMonitor(Mutex::leaf,
>> "ParallelHProfWriter_lock", Mutex::_safepoint_check_always);
>
> If you change these locks to _safepoint_check_always, you have to acquire
> them without the Mutex::_no_safepoint_check flags so I don't know why you
> don't get that assert.
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.
-------------
PR: https://git.openjdk.java.net/jdk/pull/5681
