A part of this issue was contributed with the following changeset:
commit ea23e7333e03abb4aca3e9f3854bab418a4b70e2
Author: Daniel D. Daugherty <[dcu...@openjdk.org](mailto:dcu...@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`.
-------------
Commit messages:
- 8286960: Test serviceability/jvmti/vthread/SuspendResume2 crashed: missing
ThreadsListHandle in calling context
Changes: https://git.openjdk.java.net/jdk/pull/8878/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8878&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8286960
Stats: 17 lines in 2 files changed: 8 ins; 7 del; 2 mod
Patch: https://git.openjdk.java.net/jdk/pull/8878.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/8878/head:pull/8878
PR: https://git.openjdk.java.net/jdk/pull/8878
