Fix EventSource deadlock (#71574)

* Fix EventSource deadlock

Initializing NativeRuntimeEventSource inside the EventListener static constructor
could lead to a deadlock where a 2nd thread holding the ETW lock calls back
though ETWCallback and tries to get EventListener lock which blocks on the
static constructor.

Fixes #70870

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs

@@ -4070,15 +4070,6 @@ public class EventListener : IDisposable
         /// </summary>
         public event EventHandler<EventWrittenEventArgs>? EventWritten;
 
-        static EventListener()
-        {
-#if FEATURE_PERFTRACING
-            // This allows NativeRuntimeEventSource to get initialized so that EventListeners can subscribe to the runtime events emitted from
-            // native side.
-            GC.KeepAlive(NativeRuntimeEventSource.Log);
-#endif
-        }
-
         /// <summary>
         /// Create a new EventListener in which all events start off turned off (use EnableEvents to turn
         /// them on).
@@ -4487,7 +4478,18 @@ internal static object EventListenersLock
             get
             {
                 if (s_EventSources == null)
+                {
                     Interlocked.CompareExchange(ref s_EventSources, new List<WeakReference<EventSource>>(2), null);
+#if FEATURE_PERFTRACING
+                    // It is possible that another thread could observe the s_EventSources list at this point and it
+                    // won't have the NativeRuntimeEventSource in it. In the past we guaranteed that the NativeRuntimeEventSource
+                    // was always visible in the list by initializing it in the EventListener static constructor, however doing it
+                    // that way triggered deadlocks between the static constructor and an OS ETW lock. There is no known issue here
+                    // having a small window of time where NativeRuntimeEventSource is not in the list as long
+                    // as we still guarantee it gets initialized eventually.
+                    GC.KeepAlive(NativeRuntimeEventSource.Log);
+#endif
+                }
                 return s_EventSources;
             }
         }