RFR: 8256830: misc tests failed with "assert(env->is_enabled(JVMTI_EVENT_OBJECT_FREE)) failed: checking" [v2]

[Kim Barrett]

On Tue, 1 Dec 2020 02:22:57 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> void JvmtiTagMap::flush_object_free_events() {
>>   assert_not_at_safepoint();
>>   if (env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
>> 
>> Called by JVMTI to disable events and called by the service thread.  And here for get_objects_with_tags:
>> 
>>   if (collector.some_dead_found() && env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
>>     post_dead_objects_on_vm_thread();
>>   }
>
> That isn't quite what I asked. The claim is that `remove_dead_entries_locked` needs to recheck `is_enabled` if `post_object_free` is true in case the enabled state changed from true to false. But I can't see how such a situation can arise. In `flush_object_free_events` we only call `remove_dead_entries(false)` and that is when events were seen to be disabled.

I think you've missed the indirect remove_dead_entries(true) via
post_dead_objects_on_vm_thread() in the enabled case, over on the vmthread.
And that's exactly the case that shows up in the hs_err file.  The assert
happens on the vmthread, in the VMOp used by post_dead_entries_xxx:

Stack: [0x00007f07456c6000,0x00007f07457c6000],  sp=0x00007f07457c48c0,  free space=1018k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0x11e92fc]  JvmtiExport::post_object_free(JvmtiEnv*, long)+0x8c
V  [libjvm.so+0x12293b2]  JvmtiTagMapTable::remove_dead_entries(JvmtiEnv*, bool)+0x192
V  [libjvm.so+0x12212cd]  VM_JvmtiPostObjectFree::doit()+0x5d
V  [libjvm.so+0x198469a]  VM_Operation::evaluate()+0x18a
V  [libjvm.so+0x19a7e7f]  VMThread::evaluate_operation(VM_Operation*)+0x17f
V  [libjvm.so+0x19a88cc]  VMThread::inner_execute(VM_Operation*)+0x17c
V  [libjvm.so+0x19a8b85]  VMThread::loop()+0xb5
V  [libjvm.so+0x19a8cba]  VMThread::run()+0xca
V  [libjvm.so+0x1893db0]  Thread::call_run()+0x100
V  [libjvm.so+0x1574796]  thread_native_entry(Thread*)+0x116

-------------

PR: https://git.openjdk.java.net/jdk/pull/1439