Bug ID: JDK-8255282 Compiler calls Dependencies::find_finalizable_subclass without Compile

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JDK 16
16Resolved

ciInstanceKlass::has_finalizable_subclass() seems to be buggy. It should hold the Compile_lock, because Dependencies::find_finalizable_subclass walks Klass::_next_sibling, which is protected by Compile_lock

https://github.com/openjdk/jdk/blob/d8d91977127405c4c632add48f2bb310ad60c93c/src/hotspot/share/ci/ciInstanceKlass.cpp#L397

bool ciInstanceKlass::has_finalizable_subclass() {
  if (!is_loaded())     return true;
  VM_ENTRY_MARK;
  return Dependencies::find_finalizable_subclass(get_instanceKlass()) != NULL;
}

https://github.com/openjdk/jdk/blob/d8d91977127405c4c632add48f2bb310ad60c93c/src/hotspot/share/code/dependencies.cpp#L1536

Klass* Dependencies::find_finalizable_subclass(Klass* k) {
  if (k->is_interface()) return NULL;
  if (k->has_finalizer()) return k;
  k = k->subklass();
  while (k != NULL) {
    Klass* result = find_finalizable_subclass(k);
    if (result != NULL) return result;
    k = k->next_sibling();
  }
  return NULL;
}

[~thartmann] I fixed my comment above and closed this bug as Not an Issue.
26-10-2020
According to [~coleenp] The Klass::subklass and sibling links are intentionally lock free - they do not use the Compile_lock. The one instance of adding it under the Compile_lock is mostly left there for the other things under the lock, and the comment above Klass::subklass() is left there from an earlier implementation. That whole data structure was made lock free for concurrent class unloading.
26-10-2020
Did you mean "That whole data structure was made lock _free_ for concurrent class unloading."? Should we close this as "Not an Issue" then?
26-10-2020
ILW = Potential race condition in dependency handling code, no known failures (found by manual inspection), no workaround = MMH = P3
23-10-2020