8376621: Should not suspend thread in start_transition if _is_disable_suspend set

Reviewed-by: dholmes, sspitsyn

src/hotspot/share/runtime/continuation.cpp

@@ -87,7 +87,8 @@ class UnmountBeginMark : public StackObj {
   }
   ~UnmountBeginMark() {
     assert(!_current->is_suspended()
-           JVMTI_ONLY(|| (_current->is_vthread_transition_disabler() && _result != freeze_ok)), "must be");
+           JVMTI_ONLY(|| (_result != freeze_ok &&
+                          (_current->is_vthread_transition_disabler() || _current->is_disable_suspend()))), "must be");
     assert(_current->is_in_vthread_transition(), "must be");
 
     if (_result != freeze_ok) {

src/hotspot/share/runtime/javaThread.hpp

@@ -873,7 +873,7 @@ public:
   // Atomic version; invoked by a thread other than the owning thread.
   bool in_critical_atomic() { return AtomicAccess::load(&_jni_active_critical) > 0; }
 
-  bool jni_deferred_suspension() { return AtomicAccess::load(&_jni_deferred_suspension_count); }
+  bool jni_deferred_suspension() const { return AtomicAccess::load(&_jni_deferred_suspension_count); }
   inline void enter_jni_deferred_suspension();
   void exit_jni_deferred_suspension() {
     precond(Thread::current() == this);

src/hotspot/share/runtime/mountUnmountDisabler.cpp

@@ -129,7 +129,7 @@ bool MountUnmountDisabler::is_start_transition_disabled(JavaThread* thread, oop
   int base_disable_count = notify_jvmti_events() ? 1 : 0;
   return java_lang_Thread::vthread_transition_disable_count(vthread) > 0
          || global_vthread_transition_disable_count() > base_disable_count
-         JVMTI_ONLY(|| (!thread->is_vthread_transition_disabler() &&
+         JVMTI_ONLY(|| (!thread->is_vthread_transition_disabler() && !thread->is_disable_suspend() &&
                         (JvmtiVTSuspender::is_vthread_suspended(java_lang_Thread::thread_id(vthread)) || thread->is_suspended())));
 }
 

test/hotspot/jtreg/serviceability/jvmti/vthread/SuspendResume4/SuspendResume4.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8376621
+ * @summary Suspend virtual thread while it's inside disableSuspendAndPreempt region
+ * @requires vm.continuations
+ * @requires vm.jvmti
+ * @library /test/lib /test/hotspot/jtreg/testlibrary
+ * @run main/othervm SuspendResume4
+ */
+
+import jdk.test.lib.Utils;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+
+import java.io.File;
+
+import jvmti.JVMTIUtils;
+
+public class SuspendResume4 {
+    native static void suspendThread(Thread thread);
+    native static void resumeThread(Thread thread);
+
+    public static void main(String[] args) throws Exception {
+        // Run test in child VM where Locale won't be initialized already by jtreg
+        ProcessBuilder pb = ProcessTools.createTestJavaProcessBuilder(
+            "-Djava.library.path=" + Utils.TEST_NATIVE_PATH,
+            "-agentpath:" + Utils.TEST_NATIVE_PATH + File.separator + System.mapLibraryName("SuspendResume4"),
+            "SuspendResume4$Test");
+        OutputAnalyzer output = ProcessTools.executeProcess(pb);
+        System.out.println(output.getStdout());
+        output.shouldHaveExitValue(0);
+    }
+
+    static class Test{
+        static String targetName;
+
+        private void runTest() throws Exception {
+            // start target vthread
+            Thread target = Thread.ofVirtual().name("target").start(() -> {
+                // Give time for reader to get suspended in
+                // disableSuspendAndPreempt region.
+                spinWaitMillis(100);
+                // Force unmounting. If reader was suspended inside
+                // disableSuspendAndPreempt region this will block
+                // in VirtualThread.unmount.
+                Thread.yield();
+            });
+
+            // start clinit contender
+            Thread contender = Thread.ofPlatform().name("contender").start(() -> {
+                "JAVA".toLowerCase(java.util.Locale.ROOT);
+            });
+
+            // start vthread that reads target's state
+            Thread reader = Thread.ofVirtual().name("reader").start(() -> {
+                targetName = "name: " + target;
+            });
+
+            // start suspend/resumer
+            Thread suspender = Thread.ofPlatform().name("suspender").start(() -> {
+                SuspendResume4.suspendThread(reader);
+                // Give target time for Thread.yield
+                spinWaitMillis(100);
+                SuspendResume4.resumeThread(reader);
+            });
+
+            target.join();
+            contender.join();
+            suspender.join();
+            reader.join();
+        }
+
+        public static void main(String[] args) throws Exception {
+            Test obj = new Test();
+            obj.runTest();
+        }
+
+        static void spinWaitMillis(long millis) {
+            long durationNanos = millis * 1_000_000L;
+            long start = System.nanoTime();
+            while (System.nanoTime() - start < durationNanos) {
+                Thread.onSpinWait();
+            }
+        }
+    }
+}

test/hotspot/jtreg/serviceability/jvmti/vthread/SuspendResume4/libSuspendResume4.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include <jni.h>
+#include <jvmti.h>
+#include <stdio.h>
+#include <string.h>
+#include "jvmti_common.hpp"
+
+// set by Agent_OnLoad
+static jvmtiEnv* jvmti = nullptr;
+
+extern "C" {
+
+JNIEXPORT void JNICALL
+Java_SuspendResume4_suspendThread(JNIEnv* jni, jclass klass, jthread thread) {
+  jvmtiError err = jvmti->SuspendThread(thread);
+  if (err != JVMTI_ERROR_NONE && err != JVMTI_ERROR_THREAD_NOT_ALIVE) {
+    jni->FatalError("error in JVMTI SuspendThread");
+  }
+}
+
+JNIEXPORT void JNICALL
+Java_SuspendResume4_resumeThread(JNIEnv* jni, jclass klass, jthread thread) {
+  jvmtiError err = jvmti->ResumeThread(thread);
+  if (err != JVMTI_ERROR_NONE && err != JVMTI_ERROR_THREAD_NOT_ALIVE) {
+    jni->FatalError("error in JVMTI ResumeThread");
+  }
+}
+
+JNIEXPORT jint JNICALL
+Agent_OnLoad(JavaVM* jvm, char* options, void* reserved) {
+  jvmtiCapabilities caps;
+  jvmtiError err;
+
+  printf("Agent_OnLoad: started\n");
+  if (jvm->GetEnv((void **) (&jvmti), JVMTI_VERSION) != JNI_OK) {
+    LOG("Agent_OnLoad: error in GetEnv");
+    return JNI_ERR;
+  }
+
+  memset(&caps, 0, sizeof(caps));
+  caps.can_suspend = 1;
+  err = jvmti->AddCapabilities(&caps);
+  if (err != JVMTI_ERROR_NONE) {
+    LOG("Agent_OnLoad: error in JVMTI AddCapabilities: %d\n", err);
+  }
+
+  printf("Agent_OnLoad: finished\n");
+
+  return 0;
+}
+
+} // extern "C"