Acquire VThreadInspector before vmThreadListMutex to avoid deadlock

VirtualThreads.park performs operations in the below order: Set VThreadInspector to -1 and then acquire vmThreadListMutex JVMTI GetThreadState -> ... -> getVMThread follows the below order: Acquire vmThreadListMutex and then spin until VThreadInspector != -1 A deadlock occurs because the order of operations is inconsistent between VirtualThreads.park and JVMTI GetThreadState. To resolve the deadlock, the operations in getVMThread are swapped to match the operations in VirtualThreads.park: Acquire VThreadInspector and then acquire vmThreadListMutex Related: eclipse-openj9#18642 Signed-off-by: Babneet Singh <[email protected]>
babsingh · Dec 20, 2023 · dfb02ce · dfb02ce
1 parent 012884b
commit dfb02ce
Showing 1 changed file with 10 additions and 5 deletions.
diff --git a/runtime/jvmti/jvmtiHelpers.cpp b/runtime/jvmti/jvmtiHelpers.cpp
@@ -148,16 +148,21 @@ getVMThread(J9VMThread *currentThread, jthread thread, J9VMThread **vmThreadPtr,
 		}
 	}
 
+#if JAVA_SPEC_VERSION >= 19
+	isVirtualThread = IS_JAVA_LANG_VIRTUALTHREAD(currentThread, threadObject);
+	if (isVirtualThread) {
+		vm->internalVMFunctions->acquireVThreadInspector(currentThread, thread, TRUE);
+		/* Re-fetch threadObject since acquireVThreadInspector can release and reacquire VM access. */
+                threadObject = J9_JNI_UNWRAP_REFERENCE(thread);
+	}
+#endif /* JAVA_SPEC_VERSION >= 19 */
+
 	/* Make sure the vmThread stays alive while it is being used. */
 	omrthread_monitor_enter(vm->vmThreadListMutex);
 #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);
-		/* 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) {
@@ -173,12 +178,12 @@ getVMThread(J9VMThread *currentThread, jthread thread, J9VMThread **vmThreadPtr,
 
 	if (!isThreadAlive) {
 		if (OMR_ARE_ANY_BITS_SET(flags, J9JVMTI_GETVMTHREAD_ERROR_ON_DEAD_THREAD)) {
+			omrthread_monitor_exit(vm->vmThreadListMutex);
 #if JAVA_SPEC_VERSION >= 19
 			if (isVirtualThread) {
 				vm->internalVMFunctions->releaseVThreadInspector(currentThread, thread);
 			}
 #endif /* JAVA_SPEC_VERSION >= 19 */
-			omrthread_monitor_exit(vm->vmThreadListMutex);
 			return JVMTI_ERROR_THREAD_NOT_ALIVE;
 		}
 	}