Integrated: 8373366: HandshakeState should disallow suspend ops for disabler threads

[Serguei Spitsyn]

On Wed, 10 Dec 2025 10:18:11 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> An asynchronous handshake operation (`ThreadSelfSuspensionHandshakeClosure`) can be installed when the target thread is not in a `MountUnmountDisabler` scope. But the target thread can enter such scope by the time the operation is self-processed by the target thread.
> 
> This is fixed by a small tweak in the function
> `HandshakeOperation* HandshakeState::get_op_for_self(bool allow_suspend, bool check_async_exception)`.
> The tweak is to skip a `HandshakeOperation` if `_handshakee->is_vthread_transition_disabler() == true`, so the same temporary suspension disabling mechanism would be used as for `_handshakee->is_disable_suspend() == true`.
> 
> All other changes are to move the `is_vthread_transition_disabler()` out of DEBUG to product.
> 
> Testing:
>  - In progress: mach5 tiers 1-6

This pull request has now been integrated.

Changeset: 3d919ad4
Author:    Serguei Spitsyn <sspitsyn at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3d919ad43a041eb60ce51e78831c77fd3b109aee
Stats:     290 lines in 7 files changed: 270 ins; 4 del; 16 mod

8373366: HandshakeState should disallow suspend ops for disabler threads
8375362: Deadlock with unmount of suspended virtual thread interrupting another virtual thread

Reviewed-by: lmesnik, pchilanomate

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PR: https://git.openjdk.org/jdk/pull/28740