Hi Coleen,
I have some questions.
Both the compiler method load and unload are posted as deferred events.
Both events keep the nmethod alive until the ServiceThread processes the
event.
The implementation is:
JvmtiDeferredEvent
JvmtiDeferredEvent::compiled_method_load_event(nmethod* nm) {
. . .
// Keep the nmethod alive until the ServiceThread can process
// this deferred event.
nmethodLocker::lock_nmethod(nm);
return event;
}
JvmtiDeferredEvent
JvmtiDeferredEvent::compiled_method_unload_event(nmethod* nm, jmethodID
id, const void* code) {
. . .
// Keep the nmethod alive until the ServiceThread can process
// this deferred event. This will keep the memory for the
// generated code from being reused too early. We pass
// zombie_ok == true here so that our nmethod that was just
// made into a zombie can be locked.
nmethodLocker::lock_nmethod(nm, true /* zombie_ok */);
return event;
}
void JvmtiDeferredEvent::post() {
assert(ServiceThread::is_service_thread(Thread::current()),
"Service thread must post enqueued events");
switch(_type) {
case TYPE_COMPILED_METHOD_LOAD: {
nmethod* nm = _event_data.compiled_method_load;
JvmtiExport::post_compiled_method_load(nm);
// done with the deferred event so unlock the nmethod
nmethodLocker::unlock_nmethod(nm);
break;
}
case TYPE_COMPILED_METHOD_UNLOAD: {
nmethod* nm = _event_data.compiled_method_unload.nm;
JvmtiExport::post_compiled_method_unload(
_event_data.compiled_method_unload.method_id,
_event_data.compiled_method_unload.code_begin);
// done with the deferred event so unlock the nmethod
nmethodLocker::unlock_nmethod(nm);
break;
}
. . .
}
}
Then I wonder how is it possible for the nmethod to be not alive here?:
2168 void JvmtiExport::post_compiled_method_load(nmethod *nm) {
. . .
2173 // It's not safe to look at metadata for unloaded methods.
2174 if (!nm->is_alive()) {
2175 return;
2176 }
At least, it lokks like something else is broken.
Do I miss something important here?
Thanks,
Serguei
On 11/14/19 5:15 PM, [email protected] wrote:
Summary: Don't post information which uses metadata from unloaded
nmethods
Tested tier1-3 and 100 times with test that failed (reproduced failure
without the fix).
open webrev at http://cr.openjdk.java.net/~coleenp/2019/8173361.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8173361
Thanks,
Coleen
