No need to try hijack/suspend GC threads (#75810)

* No need to try suspend GC threads

* Same change for CoreClr + some cleanup.

src/coreclr/gc/sample/gcenv.h

@@ -122,7 +122,7 @@ class Thread
         return (alloc_context *)&m_alloc_context;
     }
 
-    void SetGCSpecial(bool fGCSpecial)
+    void SetGCSpecial()
     {
     }
 };

src/coreclr/nativeaot/Runtime/eventtrace.cpp

@@ -992,9 +992,6 @@ HRESULT ETW::GCLog::ForceGCForDiagnostics()
         ThreadStore::AttachCurrentThread();
         Thread* pThread = ThreadStore::GetCurrentThread();
 
-        // Doing this prevents the GC from trying to walk this thread's stack for roots.
-        pThread->SetGCSpecial(true);
-
         // While doing the GC, much code assumes & asserts the thread doing the GC is in
         // cooperative mode.
         pThread->DisablePreemptiveMode();

src/coreclr/nativeaot/Runtime/gcrhenv.cpp

@@ -1239,7 +1239,7 @@ bool GCToEEInterface::CreateThread(void (*threadStart)(void*), void* arg, bool i
             ThreadStore::AttachCurrentThread(false);
         }
 
-        ThreadStore::RawGetCurrentThread()->SetGCSpecial(true);
+        ThreadStore::RawGetCurrentThread()->SetGCSpecial();
 
         auto realStartRoutine = pStartContext->m_pRealStartRoutine;
         void* realContext = pStartContext->m_pRealContext;

src/coreclr/nativeaot/Runtime/thread.cpp

@@ -305,14 +305,12 @@ bool Thread::IsInitialized()
 // -----------------------------------------------------------------------------------------------------------
 // GC support APIs - do not use except from GC itself
 //
-void Thread::SetGCSpecial(bool isGCSpecial)
+void Thread::SetGCSpecial()
 {
     if (!IsInitialized())
         Construct();
-    if (isGCSpecial)
-        SetState(TSF_IsGcSpecialThread);
-    else
-        ClearState(TSF_IsGcSpecialThread);
+
+    SetState(TSF_IsGcSpecialThread);
 }
 
 bool Thread::IsGCSpecial()
@@ -603,6 +601,12 @@ void Thread::Hijack()
         return;
     }
 
+    if (IsGCSpecial())
+    {
+        // GC threads can not be forced to run preemptively, so we will not try.
+        return;
+    }
+
 #ifdef FEATURE_SUSPEND_REDIRECTION
     // if the thread is redirected, leave it as-is.
     if (IsStateSet(TSF_Redirected))

src/coreclr/nativeaot/Runtime/thread.h

@@ -263,7 +263,7 @@ class Thread : private ThreadBuffer
     //
     // GC support APIs - do not use except from GC itself
     //
-    void SetGCSpecial(bool isGCSpecial);
+    void SetGCSpecial();
     bool IsGCSpecial();
     bool CatchAtSafePoint();
 

src/coreclr/vm/gcenv.ee.cpp

@@ -1397,7 +1397,7 @@ namespace
             assert(args != nullptr);
 
             ClrFlsSetThreadType(ThreadType_GC);
-            args->Thread->SetGCSpecial(true);
+            args->Thread->SetGCSpecial();
             STRESS_LOG_RESERVE_MEM(GC_STRESSLOG_MULTIPLY);
             args->HasStarted = !!args->Thread->HasStarted();
 

src/coreclr/vm/threads.h

@@ -4260,7 +4260,7 @@ class Thread
 
     // GC calls this when creating special threads that also happen to have an EE Thread
     // object associated with them (e.g., the bgc thread).
-    void SetGCSpecial(bool fGCSpecial);
+    void SetGCSpecial();
 
 private:
 

src/coreclr/vm/threads.inl

@@ -165,10 +165,10 @@ inline bool Thread::IsGCSpecial()
     return m_fGCSpecial;
 }
 
-inline void Thread::SetGCSpecial(bool fGCSpecial)
+inline void Thread::SetGCSpecial()
 {
     LIMITED_METHOD_CONTRACT;
-    m_fGCSpecial = fGCSpecial;
+    m_fGCSpecial = true;
 }
 
 #if !defined(DACCESS_COMPILE)

src/coreclr/vm/threadsuspend.cpp

@@ -3394,6 +3394,12 @@ void ThreadSuspend::SuspendRuntime(ThreadSuspend::SUSPEND_REASON reason)
                 continue;
             }
 
+            if (thread->IsGCSpecial())
+            {
+                // GC threads can not be forced to run preemptively, so we will not try.
+                continue;
+            }
+
             // this is an interesting thread in cooperative mode, let's guide it to preemptive
 
             if (!Thread::UseContextBasedThreadRedirection())