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List:       openjdk-serviceability-dev
Subject:    Integrated: 8286960: Test serviceability/jvmti/vthread/SuspendResume2 crashed: missing ThreadsListHa
From:       Serguei Spitsyn <sspitsyn () openjdk ! java ! net>
Date:       2022-05-26 0:32:35
Message-ID: ppltJeFulEPHD2DUBzSVKqE261L3NwhCz3_d-F08VcE=.7acfcfce-ef60-40c5-8af3-3f895c841a42 () github ! com
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On Wed, 25 May 2022 07:23:36 GMT, Serguei Spitsyn <sspitsyn@openjdk.org> wrote:

> A part of this issue was contributed with the following changeset:
> 
> commit ea23e7333e03abb4aca3e9f3854bab418a4b70e2
> Author: Daniel D. Daugherty <[dcubed@openjdk.org](mailto:dcubed@openjdk.org)>
> Date: Mon Nov 8 14:45:04 2021 +0000
> 
> 8249004: Reduce ThreadsListHandle overhead in relation to direct handshakes
> Reviewed-by: coleenp, sspitsyn, dholmes, rehn
> 
> The following change in `src/hotspot/share/runtime/thread.cpp` added new assert:
> 
> bool JavaThread::java_suspend() {
> - ThreadsListHandle tlh;
> - if (!tlh.includes(this)) {
> - log_trace(thread, suspend)("JavaThread:" INTPTR_FORMAT " not on ThreadsList, no \
>                 suspension", p2i(this));
> - return false;
> - }
> + guarantee(Thread::is_JavaThread_protected(this, /* checkTLHOnly */ true),
> + "missing ThreadsListHandle in calling context.");
> return this->handshake_state()->suspend();
> }
> 
> This new assert misses a check for target thread as being current `JavaThread`.
> 
> Also, the JVMTI SuspendThread is protected with TLH:
> 
> JvmtiEnv::SuspendThread(jthread thread) {
> JavaThread* current = JavaThread::current();
> ThreadsListHandle tlh(current);              <= TLS defined here!!!
> 
> oop thread_oop = NULL;
> {
> JvmtiVTMSTransitionDisabler disabler(true); 
> 
> 
> However, it is possible that a new carrier thread (and an associated `JavaThread`) \
> can be created after the `TLH` was set and the target virtual thread can be mounted \
> on new carrier thread. Then target virtual thread will be associated with newly \
> created `JavaThread` which is unprotected by the TLH. The right way to be protected \
> from this situation it is to prevent mount state transitions with \
> `JvmtiVTMSTransitionDisabler` before the TLH is set as in the change below: 
> 
> @@ -929,13 +929,13 @@ JvmtiEnv::GetAllThreads(jint* threads_count_ptr, jthread** \
> threads_ptr) { jvmtiError
> JvmtiEnv::SuspendThread(jthread thread) {
> JavaThread* current = JavaThread::current();
> -  ThreadsListHandle tlh(current);
> 
> jvmtiError err;
> JavaThread* java_thread = NULL;
> oop thread_oop = NULL;
> {
> JvmtiVTMSTransitionDisabler disabler(true);
> +    ThreadsListHandle tlh(current);
> 
> err = get_threadOop_and_JavaThread(tlh.list(), thread, &java_thread, &thread_oop);
> if (err != JVMTI_ERROR_NONE) {
> 
> 
> 
> This problem exist in all JVMTI Suspend functions:
> `SuspendThread`, `SuspendThreadList` and `SuspendAllVirtualThreads`.

This pull request has now been integrated.

Changeset: 94811c0d
Author:    Serguei Spitsyn <sspitsyn@openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/94811c0dc7c20b0e7cb2649fe8da5061ce3d6246
                
Stats:     17 lines in 2 files changed: 8 ins; 7 del; 2 mod

8286960: Test serviceability/jvmti/vthread/SuspendResume2 crashed: missing \
ThreadsListHandle in calling context

Reviewed-by: dholmes, pchilanomate, amenkov

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

PR: https://git.openjdk.java.net/jdk/pull/8878


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