Revert "Use RAII for preventing user-code suspensions"

This reverts commit 9c8f34448e0e2b0b0b0094d75dadc3116f5610fa.

Bug: 130150240
Reason for revert: Parent causes lock-level violations in gcstress.

Change-Id: I6c29a0d37a933ac37ab835e171750c2ae5ca0599

4 files changed, 264 insertions, 252 deletions

diff --git a/openjdkjvmti/events.cc b/openjdkjvmti/events.cc
index 4f978444f8..beb864be23 100644
--- a/openjdkjvmti/events.cc
+++ b/openjdkjvmti/events.cc
@@ -59,7 +59,6 @@
 #include "thread-inl.h"
 #include "thread_list.h"
 #include "ti_phase.h"
-#include "ti_thread.h"
 #include "well_known_classes.h"
 
 namespace openjdkjvmti {
@@ -1275,48 +1274,59 @@ jvmtiError EventHandler::SetEvent(ArtJvmTiEnv* env,
 
   art::Thread* self = art::Thread::Current();
   art::Thread* target = nullptr;
-  ScopedNoUserCodeSuspension snucs(self);
-
-  bool old_state;
-  bool new_state;
-  {
-    // From now on we know we cannot get suspended by user-code.
-    // NB This does a SuspendCheck (during thread state change) so we need to
-    // make sure we don't have the 'suspend_lock' locked here.
-    art::ScopedObjectAccess soa(self);
-    art::WriterMutexLock el_mu(self, envs_lock_);
-    art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
-    jvmtiError err = ERR(INTERNAL);
-    if (thread != nullptr) {
-      if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
-        return err;
-      } else if (target->IsStillStarting() ||
-                target->GetState() == art::ThreadState::kStarting) {
-        target->Dump(LOG_STREAM(WARNING) << "Is not alive: ");
-        return ERR(THREAD_NOT_ALIVE);
-      }
+  do {
+    ThreadUtil::SuspendCheck(self);
+    art::MutexLock ucsl_mu(self, *art::Locks::user_code_suspension_lock_);
+    // Make sure we won't be suspended in the middle of holding the
+    // thread_suspend_count_lock_ by a user-code suspension. We retry and do
+    // another SuspendCheck to clear this.
+    if (ThreadUtil::WouldSuspendForUserCodeLocked(self)) {
+      continue;
     }
+    bool old_state;
+    bool new_state;
+    {
+      // From now on we know we cannot get suspended by user-code.
+      // NB This does a SuspendCheck (during thread state change) so we need to
+      // make sure we don't have the 'suspend_lock' locked here.
+      art::ScopedObjectAccess soa(self);
+      art::WriterMutexLock el_mu(self, envs_lock_);
+      art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
+      jvmtiError err = ERR(INTERNAL);
+      if (thread != nullptr) {
+        if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
+          return err;
+        } else if (target->IsStillStarting() ||
+                  target->GetState() == art::ThreadState::kStarting) {
+          target->Dump(LOG_STREAM(WARNING) << "Is not alive: ");
+          return ERR(THREAD_NOT_ALIVE);
+        }
+      }
 
-    art::WriterMutexLock ei_mu(self, env->event_info_mutex_);
-    old_state = global_mask.Test(event);
-    if (mode == JVMTI_ENABLE) {
-      env->event_masks.EnableEvent(env, target, event);
-      global_mask.Set(event);
-      new_state = true;
-    } else {
-      DCHECK_EQ(mode, JVMTI_DISABLE);
 
-      env->event_masks.DisableEvent(env, target, event);
-      RecalculateGlobalEventMaskLocked(event);
-      new_state = global_mask.Test(event);
+      {
+        art::WriterMutexLock ei_mu(self, env->event_info_mutex_);
+        old_state = global_mask.Test(event);
+        if (mode == JVMTI_ENABLE) {
+          env->event_masks.EnableEvent(env, target, event);
+          global_mask.Set(event);
+          new_state = true;
+        } else {
+          DCHECK_EQ(mode, JVMTI_DISABLE);
+
+          env->event_masks.DisableEvent(env, target, event);
+          RecalculateGlobalEventMaskLocked(event);
+          new_state = global_mask.Test(event);
+        }
+      }
     }
-  }
-  // Handle any special work required for the event type. We still have the
-  // user_code_suspend_count_lock_ so there won't be any interleaving here.
-  if (new_state != old_state) {
-    return HandleEventType(event, thread, mode == JVMTI_ENABLE);
-  }
-  return OK;
+    // Handle any special work required for the event type. We still have the
+    // user_code_suspend_count_lock_ so there won't be any interleaving here.
+    if (new_state != old_state) {
+      return HandleEventType(event, thread, mode == JVMTI_ENABLE);
+    }
+    return OK;
+  } while (true);
 }
 
 void EventHandler::HandleBreakpointEventsChanged(bool added) {
diff --git a/openjdkjvmti/ti_stack.cc b/openjdkjvmti/ti_stack.cc
index 6ad4e2a84d..b96c92aac7 100644
--- a/openjdkjvmti/ti_stack.cc
+++ b/openjdkjvmti/ti_stack.cc
@@ -1014,144 +1014,153 @@ jvmtiError StackUtil::NotifyFramePop(jvmtiEnv* env, jthread thread, jint depth)
   ArtJvmTiEnv* tienv = ArtJvmTiEnv::AsArtJvmTiEnv(env);
   art::Thread* self = art::Thread::Current();
   art::Thread* target;
-
-  ScopedNoUserCodeSuspension snucs(self);
-  // From now on we know we cannot get suspended by user-code.
-  // NB This does a SuspendCheck (during thread state change) so we need to make
-  // sure we don't have the 'suspend_lock' locked here.
-  art::ScopedObjectAccess soa(self);
-  art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
-  jvmtiError err = ERR(INTERNAL);
-  if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
-    return err;
-  }
-  if (target != self) {
-    // TODO This is part of the spec but we could easily avoid needing to do it.
-    // We would just put all the logic into a sync-checkpoint.
-    art::MutexLock tscl_mu(self, *art::Locks::thread_suspend_count_lock_);
-    if (target->GetUserCodeSuspendCount() == 0) {
-      return ERR(THREAD_NOT_SUSPENDED);
+  do {
+    ThreadUtil::SuspendCheck(self);
+    art::MutexLock ucsl_mu(self, *art::Locks::user_code_suspension_lock_);
+    // Make sure we won't be suspended in the middle of holding the thread_suspend_count_lock_ by a
+    // user-code suspension. We retry and do another SuspendCheck to clear this.
+    if (ThreadUtil::WouldSuspendForUserCodeLocked(self)) {
+      continue;
     }
-  }
-  // We hold the user_code_suspension_lock_ so the target thread is staying
-  // suspended until we are done (unless it's 'self' in which case we don't care
-  // since we aren't going to be returning).
-  // TODO We could implement this using a synchronous checkpoint and not bother
-  // with any of the suspension stuff. The spec does specifically say to return
-  // THREAD_NOT_SUSPENDED though. Find the requested stack frame.
-  std::unique_ptr<art::Context> context(art::Context::Create());
-  FindFrameAtDepthVisitor visitor(target, context.get(), depth);
-  visitor.WalkStack();
-  if (!visitor.FoundFrame()) {
-    return ERR(NO_MORE_FRAMES);
-  }
-  art::ArtMethod* method = visitor.GetMethod();
-  if (method->IsNative()) {
-    return ERR(OPAQUE_FRAME);
-  }
-  // From here we are sure to succeed.
-  bool needs_instrument = false;
-  // Get/create a shadow frame
-  art::ShadowFrame* shadow_frame =
-      visitor.GetOrCreateShadowFrame(&needs_instrument);
-  {
-    art::WriterMutexLock lk(self, tienv->event_info_mutex_);
-    if (LIKELY(!shadow_frame->NeedsNotifyPop())) {
-      // Ensure we won't miss exceptions being thrown if we get jit-compiled. We
-      // only do this for the first NotifyPopFrame.
-      target->IncrementForceInterpreterCount();
-
-      // Mark shadow frame as needs_notify_pop_
-      shadow_frame->SetNotifyPop(true);
+    // From now on we know we cannot get suspended by user-code.
+    // NB This does a SuspendCheck (during thread state change) so we need to make sure we don't
+    // have the 'suspend_lock' locked here.
+    art::ScopedObjectAccess soa(self);
+    art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
+    jvmtiError err = ERR(INTERNAL);
+    if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
+      return err;
     }
-    tienv->notify_frames.insert(shadow_frame);
-  }
-  // Make sure can we will go to the interpreter and use the shadow frames.
-  if (needs_instrument) {
-    art::Runtime::Current()->GetInstrumentation()->InstrumentThreadStack(
-        target);
-  }
-  return OK;
+    if (target != self) {
+      // TODO This is part of the spec but we could easily avoid needing to do it. We would just put
+      // all the logic into a sync-checkpoint.
+      art::MutexLock tscl_mu(self, *art::Locks::thread_suspend_count_lock_);
+      if (target->GetUserCodeSuspendCount() == 0) {
+        return ERR(THREAD_NOT_SUSPENDED);
+      }
+    }
+    // We hold the user_code_suspension_lock_ so the target thread is staying suspended until we are
+    // done (unless it's 'self' in which case we don't care since we aren't going to be returning).
+    // TODO We could implement this using a synchronous checkpoint and not bother with any of the
+    // suspension stuff. The spec does specifically say to return THREAD_NOT_SUSPENDED though.
+    // Find the requested stack frame.
+    std::unique_ptr<art::Context> context(art::Context::Create());
+    FindFrameAtDepthVisitor visitor(target, context.get(), depth);
+    visitor.WalkStack();
+    if (!visitor.FoundFrame()) {
+      return ERR(NO_MORE_FRAMES);
+    }
+    art::ArtMethod* method = visitor.GetMethod();
+    if (method->IsNative()) {
+      return ERR(OPAQUE_FRAME);
+    }
+    // From here we are sure to succeed.
+    bool needs_instrument = false;
+    // Get/create a shadow frame
+    art::ShadowFrame* shadow_frame = visitor.GetOrCreateShadowFrame(&needs_instrument);
+    {
+      art::WriterMutexLock lk(self, tienv->event_info_mutex_);
+      if (LIKELY(!shadow_frame->NeedsNotifyPop())) {
+        // Ensure we won't miss exceptions being thrown if we get jit-compiled. We only do this for
+        // the first NotifyPopFrame.
+        target->IncrementForceInterpreterCount();
+
+        // Mark shadow frame as needs_notify_pop_
+        shadow_frame->SetNotifyPop(true);
+      }
+      tienv->notify_frames.insert(shadow_frame);
+    }
+    // Make sure can we will go to the interpreter and use the shadow frames.
+    if (needs_instrument) {
+      art::Runtime::Current()->GetInstrumentation()->InstrumentThreadStack(target);
+    }
+    return OK;
+  } while (true);
 }
 
 jvmtiError StackUtil::PopFrame(jvmtiEnv* env, jthread thread) {
   art::Thread* self = art::Thread::Current();
   art::Thread* target;
-
-  ScopedNoUserCodeSuspension snucs(self);
-  // From now on we know we cannot get suspended by user-code.
-  // NB This does a SuspendCheck (during thread state change) so we need to make
-  // sure we don't have the 'suspend_lock' locked here.
-  art::ScopedObjectAccess soa(self);
-  art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
-  jvmtiError err = ERR(INTERNAL);
-  if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
-    return err;
-  }
-  {
-    art::MutexLock tscl_mu(self, *art::Locks::thread_suspend_count_lock_);
-    if (target == self || target->GetUserCodeSuspendCount() == 0) {
-      // We cannot be the current thread for this function.
-      return ERR(THREAD_NOT_SUSPENDED);
+  do {
+    ThreadUtil::SuspendCheck(self);
+    art::MutexLock ucsl_mu(self, *art::Locks::user_code_suspension_lock_);
+    // Make sure we won't be suspended in the middle of holding the thread_suspend_count_lock_ by a
+    // user-code suspension. We retry and do another SuspendCheck to clear this.
+    if (ThreadUtil::WouldSuspendForUserCodeLocked(self)) {
+      continue;
+    }
+    // From now on we know we cannot get suspended by user-code.
+    // NB This does a SuspendCheck (during thread state change) so we need to make sure we don't
+    // have the 'suspend_lock' locked here.
+    art::ScopedObjectAccess soa(self);
+    art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
+    jvmtiError err = ERR(INTERNAL);
+    if (!ThreadUtil::GetAliveNativeThread(thread, soa, &target, &err)) {
+      return err;
+    }
+    {
+      art::MutexLock tscl_mu(self, *art::Locks::thread_suspend_count_lock_);
+      if (target == self || target->GetUserCodeSuspendCount() == 0) {
+        // We cannot be the current thread for this function.
+        return ERR(THREAD_NOT_SUSPENDED);
+      }
+    }
+    JvmtiGlobalTLSData* tls_data = ThreadUtil::GetGlobalTLSData(target);
+    constexpr art::StackVisitor::StackWalkKind kWalkKind =
+        art::StackVisitor::StackWalkKind::kIncludeInlinedFrames;
+    if (tls_data != nullptr &&
+        tls_data->disable_pop_frame_depth != JvmtiGlobalTLSData::kNoDisallowedPopFrame &&
+        tls_data->disable_pop_frame_depth == art::StackVisitor::ComputeNumFrames(target,
+                                                                                 kWalkKind)) {
+      JVMTI_LOG(WARNING, env) << "Disallowing frame pop due to in-progress class-load/prepare. "
+                              << "Frame at depth " << tls_data->disable_pop_frame_depth << " was "
+                              << "marked as un-poppable by the jvmti plugin. See b/117615146 for "
+                              << "more information.";
+      return ERR(OPAQUE_FRAME);
+    }
+    // We hold the user_code_suspension_lock_ so the target thread is staying suspended until we are
+    // done.
+    std::unique_ptr<art::Context> context(art::Context::Create());
+    FindFrameAtDepthVisitor final_frame(target, context.get(), 0);
+    FindFrameAtDepthVisitor penultimate_frame(target, context.get(), 1);
+    final_frame.WalkStack();
+    penultimate_frame.WalkStack();
+
+    if (!final_frame.FoundFrame() || !penultimate_frame.FoundFrame()) {
+      // Cannot do it if there is only one frame!
+      return ERR(NO_MORE_FRAMES);
     }
-  }
-  JvmtiGlobalTLSData* tls_data = ThreadUtil::GetGlobalTLSData(target);
-  constexpr art::StackVisitor::StackWalkKind kWalkKind =
-      art::StackVisitor::StackWalkKind::kIncludeInlinedFrames;
-  if (tls_data != nullptr &&
-      tls_data->disable_pop_frame_depth !=
-          JvmtiGlobalTLSData::kNoDisallowedPopFrame &&
-      tls_data->disable_pop_frame_depth ==
-          art::StackVisitor::ComputeNumFrames(target, kWalkKind)) {
-    JVMTI_LOG(WARNING, env)
-        << "Disallowing frame pop due to in-progress class-load/prepare. "
-        << "Frame at depth " << tls_data->disable_pop_frame_depth << " was "
-        << "marked as un-poppable by the jvmti plugin. See b/117615146 for "
-        << "more information.";
-    return ERR(OPAQUE_FRAME);
-  }
-  // We hold the user_code_suspension_lock_ so the target thread is staying
-  // suspended until we are done.
-  std::unique_ptr<art::Context> context(art::Context::Create());
-  FindFrameAtDepthVisitor final_frame(target, context.get(), 0);
-  FindFrameAtDepthVisitor penultimate_frame(target, context.get(), 1);
-  final_frame.WalkStack();
-  penultimate_frame.WalkStack();
-
-  if (!final_frame.FoundFrame() || !penultimate_frame.FoundFrame()) {
-    // Cannot do it if there is only one frame!
-    return ERR(NO_MORE_FRAMES);
-  }
 
-  art::ArtMethod* called_method = final_frame.GetMethod();
-  art::ArtMethod* calling_method = penultimate_frame.GetMethod();
-  if (calling_method->IsNative() || called_method->IsNative()) {
-    return ERR(OPAQUE_FRAME);
-  }
-  // From here we are sure to succeed.
-
-  // Get/create a shadow frame
-  bool created_final_frame = false;
-  bool created_penultimate_frame = false;
-  art::ShadowFrame* called_shadow_frame =
-      final_frame.GetOrCreateShadowFrame(&created_final_frame);
-  art::ShadowFrame* calling_shadow_frame =
-      penultimate_frame.GetOrCreateShadowFrame(&created_penultimate_frame);
-
-  CHECK_NE(called_shadow_frame, calling_shadow_frame)
-      << "Frames at different depths not different!";
-
-  // Tell the shadow-frame to return immediately and skip all exit events.
-  called_shadow_frame->SetForcePopFrame(true);
-  calling_shadow_frame->SetForceRetryInstruction(true);
-
-  // Make sure can we will go to the interpreter and use the shadow frames. The
-  // early return for the final frame will force everything to the interpreter
-  // so we only need to instrument if it was not present.
-  if (created_final_frame) {
-    DeoptManager::Get()->DeoptimizeThread(target);
-  }
-  return OK;
+    art::ArtMethod* called_method = final_frame.GetMethod();
+    art::ArtMethod* calling_method = penultimate_frame.GetMethod();
+    if (calling_method->IsNative() || called_method->IsNative()) {
+      return ERR(OPAQUE_FRAME);
+    }
+    // From here we are sure to succeed.
+
+    // Get/create a shadow frame
+    bool created_final_frame = false;
+    bool created_penultimate_frame = false;
+    art::ShadowFrame* called_shadow_frame =
+        final_frame.GetOrCreateShadowFrame(&created_final_frame);
+    art::ShadowFrame* calling_shadow_frame =
+        penultimate_frame.GetOrCreateShadowFrame(&created_penultimate_frame);
+
+    CHECK_NE(called_shadow_frame, calling_shadow_frame)
+        << "Frames at different depths not different!";
+
+    // Tell the shadow-frame to return immediately and skip all exit events.
+    called_shadow_frame->SetForcePopFrame(true);
+    calling_shadow_frame->SetForceRetryInstruction(true);
+
+    // Make sure can we will go to the interpreter and use the shadow frames. The early return for
+    // the final frame will force everything to the interpreter so we only need to instrument if it
+    // was not present.
+    if (created_final_frame) {
+      DeoptManager::Get()->DeoptimizeThread(target);
+    }
+    return OK;
+  } while (true);
 }
 
 }  // namespace openjdkjvmti
diff --git a/openjdkjvmti/ti_thread.cc b/openjdkjvmti/ti_thread.cc
index 15fdfb3ab5..01cc8c7699 100644
--- a/openjdkjvmti/ti_thread.cc
+++ b/openjdkjvmti/ti_thread.cc
@@ -65,30 +65,6 @@ static const char* kJvmtiTlsKey = "JvmtiTlsKey";
 
 art::ArtField* ThreadUtil::context_class_loader_ = nullptr;
 
-ScopedNoUserCodeSuspension::ScopedNoUserCodeSuspension(art::Thread* self) : self_(self) {
-  DCHECK_EQ(self, art::Thread::Current());
-  // Loop until we both have the user_code_suspension_locK_ and don't have any pending user_code
-  // suspensions.
-  do {
-    art::Locks::user_code_suspension_lock_->AssertNotHeld(self_);
-    ThreadUtil::SuspendCheck(self_);
-
-    art::Locks::user_code_suspension_lock_->ExclusiveLock(self_);
-    if (ThreadUtil::WouldSuspendForUserCodeLocked(self_)) {
-      art::Locks::user_code_suspension_lock_->ExclusiveUnlock(self_);
-      continue;
-    }
-
-    art::Locks::user_code_suspension_lock_->AssertHeld(self_);
-
-    return;
-  } while (true);
-}
-
-ScopedNoUserCodeSuspension::~ScopedNoUserCodeSuspension() {
-  art::Locks::user_code_suspension_lock_->ExclusiveUnlock(self_);
-}
-
 struct ThreadCallback : public art::ThreadLifecycleCallback {
   jthread GetThreadObject(art::Thread* self) REQUIRES_SHARED(art::Locks::mutator_lock_) {
     if (self->GetPeer() == nullptr) {
@@ -568,8 +544,17 @@ jvmtiError ThreadUtil::GetThreadState(jvmtiEnv* env ATTRIBUTE_UNUSED,
 
   art::Thread* self = art::Thread::Current();
   InternalThreadState state = {};
-  {
-    ScopedNoUserCodeSuspension snucs(self);
+  // Loop since we need to bail out and try again if we would end up getting suspended while holding
+  // the user_code_suspension_lock_ due to a SuspendReason::kForUserCode. In this situation we
+  // release the lock, wait to get resumed and try again.
+  do {
+    SuspendCheck(self);
+    art::MutexLock ucsl_mu(self, *art::Locks::user_code_suspension_lock_);
+    if (WouldSuspendForUserCodeLocked(self)) {
+      // Make sure we won't be suspended in the middle of holding the thread_suspend_count_lock_ by
+      // a user-code suspension. We retry and do another SuspendCheck to clear this.
+      continue;
+    }
     art::ScopedObjectAccess soa(self);
     art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
     jvmtiError err = ERR(INTERNAL);
@@ -578,23 +563,24 @@ jvmtiError ThreadUtil::GetThreadState(jvmtiEnv* env ATTRIBUTE_UNUSED,
       return err;
     }
     state = GetNativeThreadState(target);
-    if (state.art_state != art::ThreadState::kStarting) {
-      DCHECK(state.native_thread != nullptr);
+    if (state.art_state == art::ThreadState::kStarting) {
+      break;
+    }
+    DCHECK(state.native_thread != nullptr);
 
-      // Translate internal thread state to JVMTI and Java state.
-      jint jvmti_state = GetJvmtiThreadStateFromInternal(state);
+    // Translate internal thread state to JVMTI and Java state.
+    jint jvmti_state = GetJvmtiThreadStateFromInternal(state);
 
-      // Java state is derived from nativeGetState.
-      // TODO: Our implementation assigns "runnable" to suspended. As such, we will have slightly
-      //       different mask if a thread got suspended due to user-code. However, this is for
-      //       consistency with the Java view.
-      jint java_state = GetJavaStateFromInternal(state);
+    // Java state is derived from nativeGetState.
+    // TODO: Our implementation assigns "runnable" to suspended. As such, we will have slightly
+    //       different mask if a thread got suspended due to user-code. However, this is for
+    //       consistency with the Java view.
+    jint java_state = GetJavaStateFromInternal(state);
 
-      *thread_state_ptr = jvmti_state | java_state;
+    *thread_state_ptr = jvmti_state | java_state;
 
-      return ERR(NONE);
-    }
-  }
+    return ERR(NONE);
+  } while (true);
 
   DCHECK_EQ(state.art_state, art::ThreadState::kStarting);
 
@@ -871,7 +857,18 @@ jvmtiError ThreadUtil::SuspendOther(art::Thread* self,
   // the user_code_suspension_lock_ due to a SuspendReason::kForUserCode. In this situation we
   // release the lock, wait to get resumed and try again.
   do {
-    ScopedNoUserCodeSuspension snucs(self);
+    // Suspend ourself if we have any outstanding suspends. This is so we won't suspend due to
+    // another SuspendThread in the middle of suspending something else potentially causing a
+    // deadlock. We need to do this in the loop because if we ended up back here then we had
+    // outstanding SuspendReason::kForUserCode suspensions and we should wait for them to be cleared
+    // before continuing.
+    SuspendCheck(self);
+    art::MutexLock mu(self, *art::Locks::user_code_suspension_lock_);
+    if (WouldSuspendForUserCodeLocked(self)) {
+      // Make sure we won't be suspended in the middle of holding the thread_suspend_count_lock_ by
+      // a user-code suspension. We retry and do another SuspendCheck to clear this.
+      continue;
+    }
     // We are not going to be suspended by user code from now on.
     {
       art::ScopedObjectAccess soa(self);
@@ -960,44 +957,51 @@ jvmtiError ThreadUtil::ResumeThread(jvmtiEnv* env ATTRIBUTE_UNUSED,
   }
   art::Thread* self = art::Thread::Current();
   art::Thread* target;
-
-  // Make sure we won't get suspended ourselves while in the middle of resuming another thread.
-  ScopedNoUserCodeSuspension snucs(self);
-  // From now on we know we cannot get suspended by user-code.
-  {
-    // NB This does a SuspendCheck (during thread state change) so we need to make sure we don't
-    // have the 'suspend_lock' locked here.
-    art::ScopedObjectAccess soa(self);
-    art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
-    jvmtiError err = ERR(INTERNAL);
-    if (!GetAliveNativeThread(thread, soa, &target, &err)) {
-      return err;
-    } else if (target == self) {
-      // We would have paused until we aren't suspended anymore due to the ScopedObjectAccess so
-      // we can just return THREAD_NOT_SUSPENDED. Unfortunately we cannot do any real DCHECKs
-      // about current state since it's all concurrent.
-      return ERR(THREAD_NOT_SUSPENDED);
+  // Retry until we know we won't get suspended by user code while resuming something.
+  do {
+    SuspendCheck(self);
+    art::MutexLock ucsl_mu(self, *art::Locks::user_code_suspension_lock_);
+    if (WouldSuspendForUserCodeLocked(self)) {
+      // Make sure we won't be suspended in the middle of holding the thread_suspend_count_lock_ by
+      // a user-code suspension. We retry and do another SuspendCheck to clear this.
+      continue;
     }
-    // The JVMTI spec requires us to return THREAD_NOT_SUSPENDED if it is alive but we really
-    // cannot tell why resume failed.
+    // From now on we know we cannot get suspended by user-code.
     {
-      art::MutexLock thread_suspend_count_mu(self, *art::Locks::thread_suspend_count_lock_);
-      if (target->GetUserCodeSuspendCount() == 0) {
+      // NB This does a SuspendCheck (during thread state change) so we need to make sure we don't
+      // have the 'suspend_lock' locked here.
+      art::ScopedObjectAccess soa(self);
+      art::MutexLock tll_mu(self, *art::Locks::thread_list_lock_);
+      jvmtiError err = ERR(INTERNAL);
+      if (!GetAliveNativeThread(thread, soa, &target, &err)) {
+        return err;
+      } else if (target == self) {
+        // We would have paused until we aren't suspended anymore due to the ScopedObjectAccess so
+        // we can just return THREAD_NOT_SUSPENDED. Unfortunately we cannot do any real DCHECKs
+        // about current state since it's all concurrent.
         return ERR(THREAD_NOT_SUSPENDED);
       }
+      // The JVMTI spec requires us to return THREAD_NOT_SUSPENDED if it is alive but we really
+      // cannot tell why resume failed.
+      {
+        art::MutexLock thread_suspend_count_mu(self, *art::Locks::thread_suspend_count_lock_);
+        if (target->GetUserCodeSuspendCount() == 0) {
+          return ERR(THREAD_NOT_SUSPENDED);
+        }
+      }
     }
-  }
-  // It is okay that we don't have a thread_list_lock here since we know that the thread cannot
-  // die since it is currently held suspended by a SuspendReason::kForUserCode suspend.
-  DCHECK(target != self);
-  if (!art::Runtime::Current()->GetThreadList()->Resume(target,
-                                                        art::SuspendReason::kForUserCode)) {
-    // TODO Give a better error.
-    // This is most likely THREAD_NOT_SUSPENDED but we cannot really be sure.
-    return ERR(INTERNAL);
-  } else {
-    return OK;
-  }
+    // It is okay that we don't have a thread_list_lock here since we know that the thread cannot
+    // die since it is currently held suspended by a SuspendReason::kForUserCode suspend.
+    DCHECK(target != self);
+    if (!art::Runtime::Current()->GetThreadList()->Resume(target,
+                                                          art::SuspendReason::kForUserCode)) {
+      // TODO Give a better error.
+      // This is most likely THREAD_NOT_SUSPENDED but we cannot really be sure.
+      return ERR(INTERNAL);
+    } else {
+      return OK;
+    }
+  } while (true);
 }
 
 static bool IsCurrentThread(jthread thr) {
diff --git a/openjdkjvmti/ti_thread.h b/openjdkjvmti/ti_thread.h
index c5443bfb9f..39f1f0725c 100644
--- a/openjdkjvmti/ti_thread.h
+++ b/openjdkjvmti/ti_thread.h
@@ -52,17 +52,6 @@ namespace openjdkjvmti {
 
 class EventHandler;
 
-// Gains the user_code_suspension_lock_ and ensures that the code will not suspend for user-code.
-class SCOPED_CAPABILITY ScopedNoUserCodeSuspension {
- public:
-  explicit ScopedNoUserCodeSuspension(art::Thread* self)
-      ACQUIRE(art::Locks::user_code_suspension_lock_);
-  ~ScopedNoUserCodeSuspension() RELEASE(art::Locks::user_code_suspension_lock_);
-
- private:
-  art::Thread* self_;
-};
-
 // The struct that we store in the art::Thread::custom_tls_ that maps the jvmtiEnvs to the data
 // stored with that thread. This is needed since different jvmtiEnvs are not supposed to share TLS
 // data but we only have a single slot in Thread objects to store data.