8274298: JFR Thread Sampler thread must not acquire malloc lock after…

… suspending a thread because of possible deadlock

Reviewed-by: egahlin

src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp

@@ -27,8 +27,10 @@
 #include "jfr/recorder/jfrRecorder.hpp"
 #include "jfr/periodic/sampling/jfrCallTrace.hpp"
 #include "jfr/periodic/sampling/jfrThreadSampler.hpp"
+#include "jfr/recorder/checkpoint/types/traceid/jfrTraceIdLoadBarrier.inline.hpp"
 #include "jfr/recorder/service/jfrOptionSet.hpp"
 #include "jfr/recorder/stacktrace/jfrStackTraceRepository.hpp"
+#include "jfr/recorder/storage/jfrBuffer.hpp"
 #include "jfr/support/jfrThreadId.hpp"
 #include "jfr/support/jfrThreadLocal.hpp"
 #include "jfr/utilities/jfrTime.hpp"
@@ -323,10 +325,15 @@ class JfrThreadSampler : public NonJavaThread {
   JavaThread* _last_thread_native;
   size_t _interval_java;
   size_t _interval_native;
+  const size_t _min_size; // for enqueue buffer monitoring
+  const size_t _renew_size;
   int _cur_index;
   const u4 _max_frames;
   volatile bool _disenrolled;
 
+  const JfrBuffer* get_enqueue_buffer();
+  const JfrBuffer* renew_if_full(const JfrBuffer* enqueue_buffer);
+
   JavaThread* next_thread(ThreadsList* t_list, JavaThread* first_sampled, JavaThread* current);
   void task_stacktrace(JfrSampleType type, JavaThread** last_thread);
   JfrThreadSampler(size_t interval_java, size_t interval_native, u4 max_frames);
@@ -396,6 +403,8 @@ JfrThreadSampler::JfrThreadSampler(size_t interval_java, size_t interval_native,
   _last_thread_native(NULL),
   _interval_java(interval_java),
   _interval_native(interval_native),
+  _min_size(JfrOptionSet::stackdepth() * sizeof(intptr_t)),
+  _renew_size(_min_size * 2),
   _cur_index(-1),
   _max_frames(max_frames),
   _disenrolled(true) {
@@ -520,6 +529,15 @@ void JfrThreadSampler::post_run() {
   delete this;
 }
 
+const JfrBuffer* JfrThreadSampler::get_enqueue_buffer() {
+  const JfrBuffer* buffer = JfrTraceIdLoadBarrier::get_enqueue_buffer(this);
+  return buffer != nullptr ? renew_if_full(buffer) : JfrTraceIdLoadBarrier::renew_enqueue_buffer(_renew_size, this);
+}
+
+const JfrBuffer* JfrThreadSampler::renew_if_full(const JfrBuffer* enqueue_buffer) {
+  assert(enqueue_buffer != nullptr, "invariant");
+  return enqueue_buffer->free_size() < _min_size ? JfrTraceIdLoadBarrier::renew_enqueue_buffer(_renew_size, this) : enqueue_buffer;
+}
 
 void JfrThreadSampler::task_stacktrace(JfrSampleType type, JavaThread** last_thread) {
   ResourceMark rm;
@@ -530,7 +548,6 @@ void JfrThreadSampler::task_stacktrace(JfrSampleType type, JavaThread** last_thr
   const uint sample_limit = JAVA_SAMPLE == type ? MAX_NR_OF_JAVA_SAMPLES : MAX_NR_OF_NATIVE_SAMPLES;
   uint num_samples = 0;
   JavaThread* start = NULL;
-
   {
     elapsedTimer sample_time;
     sample_time.start();
@@ -542,6 +559,15 @@ void JfrThreadSampler::task_stacktrace(JfrSampleType type, JavaThread** last_thr
       _cur_index = tlh.list()->find_index_of_JavaThread(*last_thread);
       JavaThread* current = _cur_index != -1 ? *last_thread : NULL;
 
+      // Explicitly monitor the available space of the thread-local buffer used by the load barrier
+      // for enqueuing klasses as part of tagging methods. We do this because if space becomes sparse,
+      // we cannot rely on the implicit allocation of a new buffer as part of the regular tag mechanism.
+      // If the free list is empty, a malloc could result, and the problem with that is that the thread
+      // we have suspended could be the holder of the malloc lock. Instead, the buffer is pre-emptively
+      // renewed before thread suspension.
+      const JfrBuffer* enqueue_buffer = get_enqueue_buffer();
+      assert(enqueue_buffer != nullptr, "invariant");
+
       while (num_samples < sample_limit) {
         current = next_thread(tlh.list(), start, current);
         if (current == NULL) {
@@ -553,9 +579,11 @@ void JfrThreadSampler::task_stacktrace(JfrSampleType type, JavaThread** last_thr
         if (current->is_Compiler_thread()) {
           continue;
         }
+        assert(enqueue_buffer->free_size() >= _min_size, "invariant");
         if (sample_task.do_sample_thread(current, _frames, _max_frames, type)) {
           num_samples++;
         }
+        enqueue_buffer = renew_if_full(enqueue_buffer);
       }
       *last_thread = current;  // remember the thread we last attempted to sample
     }

src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.hpp

@@ -28,6 +28,7 @@
 #include "jfr/utilities/jfrAllocation.hpp"
 
 class JavaThread;
+class JfrBuffer;
 class JfrStackFrame;
 class JfrThreadSampler;
 class Thread;

src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdKlassQueue.cpp

@@ -247,6 +247,14 @@ void JfrTraceIdKlassQueue::enqueue(const Klass* klass) {
   _queue->enqueue(klass);
 }
 
+JfrBuffer* JfrTraceIdKlassQueue::get_enqueue_buffer(Thread* thread) {
+  return _queue->thread_local_storage(thread);
+}
+
+JfrBuffer* JfrTraceIdKlassQueue::renew_enqueue_buffer(size_t size, Thread* thread) {
+  return _queue->renew(size, thread);
+}
+
 void JfrTraceIdKlassQueue::iterate(klass_callback callback, bool previous_epoch) {
   assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
   KlassFunctor functor(callback);

src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdKlassQueue.hpp

@@ -28,6 +28,7 @@
 #include "jfr/utilities/jfrAllocation.hpp"
 #include "jfr/utilities/jfrEpochQueue.hpp"
 
+class JfrBuffer;
 class Klass;
 class Thread;
 
@@ -47,7 +48,7 @@ class KlassFunctor {
 // It details how to store and process an enqueued Klass representation. See utilities/jfrEpochQueue.hpp.
 //
 template <typename Buffer>
-class JfrEpochQueueKlassPolicy {
+class JfrEpochQueueKlassPolicy : public JfrCHeapObj {
  public:
   typedef Buffer* BufferPtr;
   typedef Klass Type;
@@ -64,8 +65,11 @@ class JfrEpochQueueKlassPolicy {
 };
 
 class JfrTraceIdKlassQueue : public JfrCHeapObj {
+  friend class JfrTraceIdLoadBarrier;
  private:
   JfrEpochQueue<JfrEpochQueueKlassPolicy>* _queue;
+  JfrBuffer* get_enqueue_buffer(Thread* thread);
+  JfrBuffer* renew_enqueue_buffer(size_t size, Thread* thread);
  public:
   JfrTraceIdKlassQueue();
   ~JfrTraceIdKlassQueue();

src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdLoadBarrier.cpp

@@ -68,3 +68,11 @@ void JfrTraceIdLoadBarrier::do_klasses(klass_callback callback, bool previous_ep
   assert_locked_or_safepoint(ClassLoaderDataGraph_lock);
   klass_queue().iterate(callback, previous_epoch);
 }
+
+JfrBuffer* JfrTraceIdLoadBarrier::get_enqueue_buffer(Thread* thread) {
+  return klass_queue().get_enqueue_buffer(thread);
+}
+
+JfrBuffer* JfrTraceIdLoadBarrier::renew_enqueue_buffer(size_t size, Thread* thread) {
+  return klass_queue().renew_enqueue_buffer(size, thread);
+}

src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdLoadBarrier.hpp

@@ -29,6 +29,7 @@
 #include "memory/allocation.hpp"
 
 class ClassLoaderData;
+class JfrBuffer;
 class Klass;
 class Method;
 class ModuleEntry;
@@ -69,12 +70,16 @@ class PackageEntry;
 class JfrTraceIdLoadBarrier : AllStatic {
   friend class Jfr;
   friend class JfrCheckpointManager;
+  friend class JfrStackTrace;
+  friend class JfrThreadSampler;
  private:
   static bool initialize();
   static void clear();
   static void destroy();
   static void enqueue(const Klass* klass);
   static void load_barrier(const Klass* klass);
+  static JfrBuffer* get_enqueue_buffer(Thread* thread);
+  static JfrBuffer* renew_enqueue_buffer(size_t size, Thread* thread);
  public:
   static traceid load(const ClassLoaderData* cld);
   static traceid load(const Klass* klass);

src/hotspot/share/jfr/recorder/stacktrace/jfrStackTrace.cpp

@@ -27,6 +27,7 @@
 #include "jfr/recorder/checkpoint/types/traceid/jfrTraceId.inline.hpp"
 #include "jfr/recorder/repository/jfrChunkWriter.hpp"
 #include "jfr/recorder/stacktrace/jfrStackTrace.hpp"
+#include "jfr/recorder/storage/jfrBuffer.hpp"
 #include "jfr/support/jfrMethodLookup.hpp"
 #include "memory/allocation.inline.hpp"
 #include "oops/instanceKlass.inline.hpp"
@@ -175,19 +176,30 @@ void vframeStreamSamples::samples_next() {
   } while (!fill_from_frame());
 }
 
+static const size_t min_valid_free_size_bytes = 16;
+
+static inline bool is_full(const JfrBuffer* enqueue_buffer) {
+  return enqueue_buffer->free_size() < min_valid_free_size_bytes;
+}
+
 bool JfrStackTrace::record_thread(JavaThread& thread, frame& frame) {
+  // Explicitly monitor the available space of the thread-local buffer used for enqueuing klasses as part of tagging methods.
+  // We do this because if space becomes sparse, we cannot rely on the implicit allocation of a new buffer as part of the
+  // regular tag mechanism. If the free list is empty, a malloc could result, and the problem with that is that the thread
+  // we have suspended could be the holder of the malloc lock. If there is no more available space, the attempt is aborted.
+  const JfrBuffer* const enqueue_buffer = JfrTraceIdLoadBarrier::get_enqueue_buffer(Thread::current());
+  assert(enqueue_buffer != nullptr, "invariant");
   vframeStreamSamples st(&thread, frame, false);
   u4 count = 0;
   _reached_root = true;
-
   _hash = 1;
   while (!st.at_end()) {
     if (count >= _max_frames) {
       _reached_root = false;
       break;
     }
     const Method* method = st.method();
-    if (!Method::is_valid_method(method)) {
+    if (!Method::is_valid_method(method) || is_full(enqueue_buffer)) {
       // we throw away everything we've gathered in this sample since
       // none of it is safe
       return false;

src/hotspot/share/jfr/utilities/jfrEpochQueue.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 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
@@ -27,6 +27,8 @@
 
 #include "jfr/recorder/storage/jfrEpochStorage.hpp"
 
+class Thread;
+
 /*
  * An ElmentPolicy template template argument provides the implementation for how elements
  * associated with the queue is encoded and managed by exposing the following members:
@@ -43,7 +45,7 @@
  *  size_t operator()(const u1* next_element, Callback& callback, bool previous_epoch = false);
  */
 template <template <typename> class ElementPolicy>
-class JfrEpochQueue : public JfrCHeapObj {
+class JfrEpochQueue : public ElementPolicy<typename JfrEpochStorage::Buffer> {
  public:
   typedef JfrEpochStorage::Buffer Buffer;
   typedef JfrEpochStorage::BufferPtr BufferPtr;
@@ -53,22 +55,20 @@ class JfrEpochQueue : public JfrCHeapObj {
   ~JfrEpochQueue();
   bool initialize(size_t min_buffer_size, size_t free_list_cache_count_limit, size_t cache_prealloc_count);
   void enqueue(TypePtr t);
+  BufferPtr renew(size_t size, Thread* thread);
   template <typename Callback>
   void iterate(Callback& callback, bool previous_epoch = false);
  private:
-  typedef ElementPolicy<Buffer> Policy;
-  Policy _policy;
   JfrEpochStorage* _storage;
   BufferPtr storage_for_element(TypePtr t, size_t element_size);
-
   template <typename Callback>
   class ElementDispatch {
    private:
     Callback& _callback;
-    Policy& _policy;
+    JfrEpochQueue& _queue;
    public:
     typedef Buffer Type;
-    ElementDispatch(Callback& callback, Policy& policy);
+    ElementDispatch(Callback& callback, JfrEpochQueue& queue);
     size_t operator()(const u1* element, bool previous_epoch);
   };
 };

src/hotspot/share/jfr/utilities/jfrEpochQueue.inline.hpp

@@ -26,13 +26,12 @@
 #define SHARE_JFR_UTILITIES_JFREPOCHQUEUE_INLINE_HPP
 
 #include "jfr/utilities/jfrEpochQueue.hpp"
-
 #include "jfr/recorder/storage/jfrEpochStorage.inline.hpp"
 #include "jfr/recorder/storage/jfrStorageUtils.inline.hpp"
 #include "runtime/thread.inline.hpp"
 
 template <template <typename> class ElementPolicy>
-JfrEpochQueue<ElementPolicy>::JfrEpochQueue() : _policy(), _storage(NULL) {}
+JfrEpochQueue<ElementPolicy>::JfrEpochQueue() : _storage(NULL) {}
 
 template <template <typename> class ElementPolicy>
 JfrEpochQueue<ElementPolicy>::~JfrEpochQueue() {
@@ -46,53 +45,69 @@ bool JfrEpochQueue<ElementPolicy>::initialize(size_t min_buffer_size, size_t fre
   return _storage != NULL && _storage->initialize(min_buffer_size, free_list_cache_count_limit, cache_prealloc_count);
 }
 
+template <template <typename> class ElementPolicy>
+inline typename JfrEpochQueue<ElementPolicy>::BufferPtr
+JfrEpochQueue<ElementPolicy>::renew(size_t size, Thread* thread) {
+  assert(thread != nullptr, "invariant");
+  BufferPtr buffer = this->thread_local_storage(thread);
+  if (buffer != nullptr) {
+    _storage->release(buffer);
+  }
+  buffer = _storage->acquire(size, thread);
+  assert(buffer != nullptr, "invariant");
+  assert(buffer->free_size() >= size, "invariant");
+  this->set_thread_local_storage(buffer, thread);
+  assert(this->thread_local_storage(thread) == buffer, "invariant");
+  return buffer;
+}
+
 template <template <typename> class ElementPolicy>
 inline typename JfrEpochQueue<ElementPolicy>::BufferPtr
 JfrEpochQueue<ElementPolicy>::storage_for_element(JfrEpochQueue<ElementPolicy>::TypePtr t, size_t element_size) {
-  assert(_policy.element_size(t) == element_size, "invariant");
+  assert(this->element_size(t) == element_size, "invariant");
   Thread* const thread = Thread::current();
-  BufferPtr buffer = _policy.thread_local_storage(thread);
-  if (buffer == NULL) {
+  BufferPtr buffer = this->thread_local_storage(thread);
+  if (buffer == nullptr) {
     buffer = _storage->acquire(element_size, thread);
-    _policy.set_thread_local_storage(buffer, thread);
+    this->set_thread_local_storage(buffer, thread);
   } else if (buffer->free_size() < element_size) {
     _storage->release(buffer);
     buffer = _storage->acquire(element_size, thread);
-    _policy.set_thread_local_storage(buffer, thread);
+    this->set_thread_local_storage(buffer, thread);
   }
   assert(buffer->free_size() >= element_size, "invariant");
-  assert(_policy.thread_local_storage(thread) == buffer, "invariant");
+  assert(this->thread_local_storage(thread) == buffer, "invariant");
   return buffer;
 }
 
 template <template <typename> class ElementPolicy>
 void JfrEpochQueue<ElementPolicy>::enqueue(JfrEpochQueue<ElementPolicy>::TypePtr t) {
-  assert(t != NULL, "invariant");
-  size_t element_size = _policy.element_size(t);
+  assert(t != nullptr, "invariant");
+  size_t element_size = this->element_size(t);
   BufferPtr buffer = storage_for_element(t, element_size);
-  assert(buffer != NULL, "invariant");
-  _policy.store_element(t, buffer);
+  assert(buffer != nullptr, "invariant");
+  this->store_element(t, buffer);
   buffer->set_pos(element_size);
 }
 
 template <template <typename> class ElementPolicy>
 template <typename Callback>
-JfrEpochQueue<ElementPolicy>::ElementDispatch<Callback>::ElementDispatch(Callback& callback, JfrEpochQueue<ElementPolicy>::Policy& policy) :
-  _callback(callback),_policy(policy) {}
+JfrEpochQueue<ElementPolicy>::ElementDispatch<Callback>::ElementDispatch(Callback& callback, JfrEpochQueue<ElementPolicy>& queue) :
+  _callback(callback), _queue(queue) {}
 
 template <template <typename> class ElementPolicy>
 template <typename Callback>
 size_t JfrEpochQueue<ElementPolicy>::ElementDispatch<Callback>::operator()(const u1* element, bool previous_epoch) {
-  assert(element != NULL, "invariant");
-  return _policy(element, _callback, previous_epoch);
+  assert(element != nullptr, "invariant");
+  return _queue(element, _callback, previous_epoch);
 }
 
 template <template <typename> class ElementPolicy>
 template <typename Callback>
 void JfrEpochQueue<ElementPolicy>::iterate(Callback& callback, bool previous_epoch) {
   typedef ElementDispatch<Callback> ElementDispatcher;
   typedef EpochDispatchOp<ElementDispatcher> QueueDispatcher;
-  ElementDispatcher element_dispatcher(callback, _policy);
+  ElementDispatcher element_dispatcher(callback, *this);
   QueueDispatcher dispatch(element_dispatcher, previous_epoch);
   _storage->iterate(dispatch, previous_epoch);
   DEBUG_ONLY(_storage->verify_previous_empty();)