RFR: 8245877: assert(_value != __null) failed: resolving NULL _value in JvmtiExport::post_compiled_method_load

[David Holmes]

On Sat, 26 Jun 2021 17:48:15 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

> The crash happens because nmethod might become a zombie before it is enqueued in JvmtiDeferredEventQueue or after it is dequeued from it. The crash is reproduced by serviceability/jvmti/CompiledMethodLoad/Zombie.java. However, it takes ~3K  runs to hit it. I verified the fix by running this test >100K on each platform. Also, I verified that protecting in 'void JvmtiDeferredEventQueue::post(JvmtiEnv* env)' is not enough.

Hi Leonid,

I'm not clear on the details here - please see comments below.

Thanks,
David

src/hotspot/share/code/nmethod.cpp line 1611:

> 1609:       return;
> 1610:     }
> 1611:     mark_as_seen_on_stack();

Not obvious what this actually does in relation to the dequeuing problem.

src/hotspot/share/prims/jvmtiImpl.cpp line 968:

> 966:   for (QueueNode* node = _queue_head; node != NULL; node = node->next()) {
> 967:     node->event().post_compiled_method_load_event(env);
> 968:   }

Can't you dequeue() immediately after calling post_compiled_method_load_event()?

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PR: https://git.openjdk.java.net/jdk/pull/4602