RFR: 8316401: sun/tools/jhsdb/JStackStressTest.java failed with "InternalError: We should have found a thread that owns the anonymous lock"

[Chris Plummer]

On Tue, 26 Sep 2023 02:42:56 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Correction, there is one code path where we pop the lockstack first and then update the owner:
>> 
>> ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
>>   if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
>>     // It must be owned by us. Pop lock object from lock stack.
>>     LockStack& lock_stack = current->lock_stack();
>>     oop popped = lock_stack.pop();
>>     assert(popped == object, "must be owned by this thread");
>>     monitor->set_owner_from_anonymous(current);
>>   }
>>   monitor->exit(current);
>> 
>> we should probably do this the other way around.
>
> Maybe SA is seeing a monitor in the monitor cache that it is only seeing because the monitor cache is currently inconsistent (due to SA not safe pointing). So the question is whether the monitor cache can be in a state where it still contains a reference to an anonymous monitor, but no thread actually owns the monitor (and the anonymous monitor is about to be purged from the cache).

Looks like you answered my question while I was asking it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15907#discussion_r1336566708