GCStress eventing fix (#28148)

Author: davmason

src/vm/eventpipe.cpp

@@ -699,11 +699,17 @@ bool EventPipe::WalkManagedStackForThread(Thread *pThread, StackContents &stackC
 
     stackContents.Reset();
 
+    // Before we call into StackWalkFrames we need to mark GC_ON_TRANSITIONS as FALSE
+    // because under GCStress runs (GCStress=0x3), a GC will be triggered for every transition,
+    // which will cause the GC to try to walk the stack while we are in the middle of walking the stack.
+    bool gcOnTransitions = GC_ON_TRANSITIONS(FALSE);
+
     StackWalkAction swaRet = pThread->StackWalkFrames(
         (PSTACKWALKFRAMESCALLBACK)&StackWalkCallback,
         &stackContents,
         ALLOW_ASYNC_STACK_WALK | FUNCTIONSONLY | HANDLESKIPPEDFRAMES | ALLOW_INVALID_OBJECTS);
 
+    GC_ON_TRANSITIONS(gcOnTransitions);
     return ((swaRet == SWA_DONE) || (swaRet == SWA_CONTINUE));
 }