Re-fetch objects after VM access is released and reacquired

Stale objects can manifest many issues. In this case, stale objects cause complex and intermittent synchronization issues. Related: eclipse-openj9#17865 Related: eclipse-openj9#17869 Related: eclipse-openj9#18370 Signed-off-by: Babneet Singh <sbabneet@ca.ibm.com>
babsingh · Nov 9, 2023 · a1cdacf · a1cdacf
1 parent 2dc399e
commit a1cdacf
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Showing 2 changed files with 15 additions and 7 deletions.
diff --git a/runtime/jvmti/jvmtiHelpers.c b/runtime/jvmti/jvmtiHelpers.c
@@ -143,10 +143,13 @@ getVMThread(J9VMThread *currentThread, jthread thread, J9VMThread **vmThreadPtr,
 #if JAVA_SPEC_VERSION >= 19
 	isVirtualThread = IS_JAVA_LANG_VIRTUALTHREAD(currentThread, threadObject);
 	if (isVirtualThread) {
+		jint vthreadState = 0;
+		j9object_t carrierThread = NULL;
 		vm->internalVMFunctions->acquireVThreadInspector(currentThread, thread, TRUE);
-
-		jint vthreadState = J9VMJAVALANGVIRTUALTHREAD_STATE(currentThread, threadObject);
-		j9object_t carrierThread = (j9object_t)J9VMJAVALANGVIRTUALTHREAD_CARRIERTHREAD(currentThread, threadObject);
+		/* Re-fetch threadObject since acquireVThreadInspector can release and reacquire VM access. */
+		threadObject = J9_JNI_UNWRAP_REFERENCE(thread);
+		vthreadState = J9VMJAVALANGVIRTUALTHREAD_STATE(currentThread, threadObject);
+		carrierThread = (j9object_t)J9VMJAVALANGVIRTUALTHREAD_CARRIERTHREAD(currentThread, threadObject);
 		if (NULL != carrierThread) {
 			targetThread = J9VMJAVALANGTHREAD_THREADREF(currentThread, carrierThread);
 		}
@@ -1659,7 +1662,7 @@ setEventNotificationMode(J9JVMTIEnv * j9env, J9VMThread * currentThread, jint mo
 	if (event_thread == NULL) {
 		eventMap = &(j9env->globalEventEnable);
 	} else {
-		j9object_t threadObject = J9_JNI_UNWRAP_REFERENCE(event_thread);
+		j9object_t threadObject = NULL;
 		J9VMThread *vmThreadForTLS = NULL;
 		rc = getVMThread(
 				currentThread, event_thread, &targetThread, JVMTI_ERROR_NONE,
@@ -1668,6 +1671,10 @@ setEventNotificationMode(J9JVMTIEnv * j9env, J9VMThread * currentThread, jint mo
 			goto done;
 		}
 		vmThreadForTLS = targetThread;
+		/* Fetch threadObject after getVMThread because getVMThread can release and
+		 * reacquire VM access.
+		 */
+		threadObject = J9_JNI_UNWRAP_REFERENCE(event_thread);
 #if JAVA_SPEC_VERSION >= 19
 		rc = allocateTLS(vm, threadObject);
 		if (JVMTI_ERROR_NONE != rc) {

diff --git a/runtime/vm/ContinuationHelpers.cpp b/runtime/vm/ContinuationHelpers.cpp
@@ -531,17 +531,18 @@ acquireVThreadInspector(J9VMThread *currentThread, jobject thread, BOOLEAN spin)
 	J9JavaVM *vm = currentThread->javaVM;
 	J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;
 	MM_ObjectAccessBarrierAPI objectAccessBarrier = MM_ObjectAccessBarrierAPI(currentThread);
-	j9object_t threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
-	I_64 vthreadInspectorCount;
+	j9object_t threadObj = NULL;
+	I_64 vthreadInspectorCount = 0;
 retry:
+	/* Consistently re-fetch threadObj for all the cases below. */
+	threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
 	vthreadInspectorCount = J9OBJECT_I64_LOAD(currentThread, threadObj, vm->virtualThreadInspectorCountOffset);
 	if (vthreadInspectorCount < 0) {
 		/* Thread is in transition, wait. */
 		vmFuncs->internalExitVMToJNI(currentThread);
 		VM_AtomicSupport::yieldCPU();
 		/* After wait, the thread may suspend here. */
 		vmFuncs->internalEnterVMFromJNI(currentThread);
-		threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
 		if (spin) {
 			goto retry;
 		} else {