RFR: 8325937: runtime/handshake/HandshakeDirectTest.java causes "monitor end should be strictly below the frame pointer" assertion failure on AArch64 [v2]

[Robbin Ehn]

On Thu, 3 Oct 2024 11:54:53 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Add missing StoreLoad fences in handshaking code to match safepoint code.  Thanks to @pchilano for finding this bug.
>> 
>> Tested with tier1-4 and tier8 which has Kitchensink in it.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove comment about state.

That is why I want a third fence here, if your shipping this:

bool HandshakeState::process_by_self(bool allow_suspend, bool check_async_exception) {
  assert(Thread::current() == _handshakee, "should call from _handshakee");
  assert(!_handshakee->is_terminated(), "should not be a terminated thread");
  _handshakee->frame_anchor()->make_walkable();
  // Threads shouldn't block if they are in the middle of printing, but...
  ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
================>FENCE<==================
  while (has_operation()) {
    // Handshakes cannot safely safepoint. The exceptions to this rule are
    // the asynchronous suspension and unsafe access error handshakes.
    MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);

As that would be for the MutexLocker which is now "missing" it. (not sure if it's problem or not)

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PR Comment: https://git.openjdk.org/jdk/pull/21295#issuecomment-2392121176