From a40ee18fc7b42fbe18d67f014190071ae2cfac35 Mon Sep 17 00:00:00 2001
From: Evgeny Astigeevich <eastig@amazon.com>
Date: Tue, 9 Jun 2026 14:11:36 +0000
Subject: [PATCH] Add SuspendedThreadTask_lock to guard
 SuspendedThreadTask::run

---
 .../jfr/periodic/sampling/jfrThreadSampler.cpp      | 11 ++++++++++-
 src/hotspot/share/runtime/hotCodeSampler.cpp        |  5 +----
 src/hotspot/share/runtime/hotCodeSampler.hpp        | 13 +++++++++++++
 src/hotspot/share/runtime/mutexLocker.cpp           |  2 ++
 src/hotspot/share/runtime/mutexLocker.hpp           |  1 +
 5 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp b/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp
index 0a8b3975139..965568c706f 100644
--- a/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp
+++ b/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp
@@ -32,6 +32,9 @@
 #include "jfr/utilities/jfrTryLock.hpp"
 #include "jfr/utilities/jfrTypes.hpp"
 #include "logging/log.hpp"
+#ifdef COMPILER2
+#include "opto/c2_globals.hpp"
+#endif
 #include "runtime/atomicAccess.hpp"
 #include "runtime/globals.hpp"
 #include "runtime/javaThread.inline.hpp"
@@ -288,7 +291,13 @@ class OSThreadSampler : public SuspendedThreadTask {
  public:
   OSThreadSampler(JavaThread* jt) : SuspendedThreadTask(jt),
                                     _result(THREAD_SUSPENSION_ERROR) {}
-  void request_sample() { run(); }
+  void request_sample() {
+    ConditionalMutexLocker ml(Thread::current(), SuspendedThreadTask_lock,
+                              COMPILER2_PRESENT(HotCodeHeap) NOT_COMPILER2(false),
+                              Mutex::_no_safepoint_check_flag);
+    run();
+  }
+
   JfrSampleResult result() const { return _result; }
 
   void do_task(const SuspendedThreadTaskContext& context) {
diff --git a/src/hotspot/share/runtime/hotCodeSampler.cpp b/src/hotspot/share/runtime/hotCodeSampler.cpp
index 4f25b0989a7..3e0b5022fed 100644
--- a/src/hotspot/share/runtime/hotCodeSampler.cpp
+++ b/src/hotspot/share/runtime/hotCodeSampler.cpp
@@ -30,9 +30,6 @@
 #include "runtime/javaThread.inline.hpp"
 
 void ThreadSampler::sample_all_java_threads() {
-  // Hold Threads_lock to coordinate with other samplers (such as JFR)
-  MutexLocker ml(Threads_lock);
-
   // Collect samples for each JavaThread
   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
     if (jt->is_hidden_from_external_view() ||
@@ -42,7 +39,7 @@ void ThreadSampler::sample_all_java_threads() {
     }
 
     GetPCTask task(jt);
-    task.run();
+    task.request_pc();
     address pc = task.pc();
     if (pc == nullptr) {
       continue;
diff --git a/src/hotspot/share/runtime/hotCodeSampler.hpp b/src/hotspot/share/runtime/hotCodeSampler.hpp
index d61cac791e1..44aa3527173 100644
--- a/src/hotspot/share/runtime/hotCodeSampler.hpp
+++ b/src/hotspot/share/runtime/hotCodeSampler.hpp
@@ -22,6 +22,8 @@
  *
  */
 
+#include "runtime/mutex.hpp"
+#include "runtime/mutexLocker.hpp"
 #ifdef COMPILER2
 #ifndef SHARE_RUNTIME_HOTCODESAMPLER_HPP
 #define SHARE_RUNTIME_HOTCODESAMPLER_HPP
@@ -75,6 +77,17 @@ class GetPCTask : public SuspendedThreadTask {
  public:
   GetPCTask(JavaThread* thread) : SuspendedThreadTask(thread), _pc(nullptr) {}
 
+  void request_pc() {
+#if INCLUDE_JFR
+    if (SuspendedThreadTask_lock->try_lock()) {
+      run();
+      SuspendedThreadTask_lock->unlock();
+    }
+#else
+    run();
+#endif
+  }
+
   address pc() const {
     return _pc;
   }
diff --git a/src/hotspot/share/runtime/mutexLocker.cpp b/src/hotspot/share/runtime/mutexLocker.cpp
index 32e7208474d..e2473bdfb04 100644
--- a/src/hotspot/share/runtime/mutexLocker.cpp
+++ b/src/hotspot/share/runtime/mutexLocker.cpp
@@ -121,6 +121,7 @@ Mutex*   Verify_lock                  = nullptr;
 Mutex*   JfrStacktrace_lock           = nullptr;
 Monitor* JfrMsg_lock                  = nullptr;
 Mutex*   JfrBuffer_lock               = nullptr;
+Mutex*   SuspendedThreadTask_lock     = nullptr;
 #endif
 
 Mutex*   CodeHeapStateAnalytics_lock  = nullptr;
@@ -280,6 +281,7 @@ void mutex_init() {
   MUTEX_DEFN(JfrBuffer_lock                  , PaddedMutex  , event);
   MUTEX_DEFN(JfrMsg_lock                     , PaddedMonitor, event);
   MUTEX_DEFN(JfrStacktrace_lock              , PaddedMutex  , event);
+  MUTEX_DEFN(SuspendedThreadTask_lock        , PaddedMutex  , nosafepoint);
 #endif
 
   MUTEX_DEFN(ContinuationRelativize_lock     , PaddedMonitor, nosafepoint-3);
diff --git a/src/hotspot/share/runtime/mutexLocker.hpp b/src/hotspot/share/runtime/mutexLocker.hpp
index 044fcb732af..aeee000b377 100644
--- a/src/hotspot/share/runtime/mutexLocker.hpp
+++ b/src/hotspot/share/runtime/mutexLocker.hpp
@@ -139,6 +139,7 @@ extern Mutex*   FinalImageRecipes_lock;          // Protecting the tables used b
 extern Mutex*   JfrStacktrace_lock;              // used to guard access to the JFR stacktrace table
 extern Monitor* JfrMsg_lock;                     // protects JFR messaging
 extern Mutex*   JfrBuffer_lock;                  // protects JFR buffer operations
+extern Mutex*   SuspendedThreadTask_lock;        // used to guard SuspendedThreadTask::run
 #endif
 
 extern Mutex*   Metaspace_lock;                  // protects Metaspace virtualspace and chunk expansions